Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1794 insertions, 0 deletions

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
new file mode 100644
index 000000000..4448758f6
--- /dev/null
+++ b/security/keys/keyring.c
@@ -0,0 +1,1794 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Keyring handling
+ *
+ * Copyright (C) 2004-2005, 2008, 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/security.h>
+#include <linux/seq_file.h>
+#include <linux/err.h>
+#include <linux/user_namespace.h>
+#include <linux/nsproxy.h>
+#include <keys/keyring-type.h>
+#include <keys/user-type.h>
+#include <linux/assoc_array_priv.h>
+#include <linux/uaccess.h>
+#include <net/net_namespace.h>
+#include "internal.h"
+
+/*
+ * When plumbing the depths of the key tree, this sets a hard limit
+ * set on how deep we're willing to go.
+ */
+#define KEYRING_SEARCH_MAX_DEPTH 6
+
+/*
+ * We mark pointers we pass to the associative array with bit 1 set if
+ * they're keyrings and clear otherwise.
+ */
+#define KEYRING_PTR_SUBTYPE	0x2UL
+
+static inline bool keyring_ptr_is_keyring(const struct assoc_array_ptr *x)
+{
+	return (unsigned long)x & KEYRING_PTR_SUBTYPE;
+}
+static inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
+{
+	void *object = assoc_array_ptr_to_leaf(x);
+	return (struct key *)((unsigned long)object & ~KEYRING_PTR_SUBTYPE);
+}
+static inline void *keyring_key_to_ptr(struct key *key)
+{
+	if (key->type == &key_type_keyring)
+		return (void *)((unsigned long)key | KEYRING_PTR_SUBTYPE);
+	return key;
+}
+
+static DEFINE_RWLOCK(keyring_name_lock);
+
+/*
+ * Clean up the bits of user_namespace that belong to us.
+ */
+void key_free_user_ns(struct user_namespace *ns)
+{
+	write_lock(&keyring_name_lock);
+	list_del_init(&ns->keyring_name_list);
+	write_unlock(&keyring_name_lock);
+
+	key_put(ns->user_keyring_register);
+#ifdef CONFIG_PERSISTENT_KEYRINGS
+	key_put(ns->persistent_keyring_register);
+#endif
+}
+
+/*
+ * The keyring key type definition.  Keyrings are simply keys of this type and
+ * can be treated as ordinary keys in addition to having their own special
+ * operations.
+ */
+static int keyring_preparse(struct key_preparsed_payload *prep);
+static void keyring_free_preparse(struct key_preparsed_payload *prep);
+static int keyring_instantiate(struct key *keyring,
+			       struct key_preparsed_payload *prep);
+static void keyring_revoke(struct key *keyring);
+static void keyring_destroy(struct key *keyring);
+static void keyring_describe(const struct key *keyring, struct seq_file *m);
+static long keyring_read(const struct key *keyring,
+			 char *buffer, size_t buflen);
+
+struct key_type key_type_keyring = {
+	.name		= "keyring",
+	.def_datalen	= 0,
+	.preparse	= keyring_preparse,
+	.free_preparse	= keyring_free_preparse,
+	.instantiate	= keyring_instantiate,
+	.revoke		= keyring_revoke,
+	.destroy	= keyring_destroy,
+	.describe	= keyring_describe,
+	.read		= keyring_read,
+};
+EXPORT_SYMBOL(key_type_keyring);
+
+/*
+ * Semaphore to serialise link/link calls to prevent two link calls in parallel
+ * introducing a cycle.
+ */
+static DEFINE_MUTEX(keyring_serialise_link_lock);
+
+/*
+ * Publish the name of a keyring so that it can be found by name (if it has
+ * one and it doesn't begin with a dot).
+ */
+static void keyring_publish_name(struct key *keyring)
+{
+	struct user_namespace *ns = current_user_ns();
+
+	if (keyring->description &&
+	    keyring->description[0] &&
+	    keyring->description[0] != '.') {
+		write_lock(&keyring_name_lock);
+		list_add_tail(&keyring->name_link, &ns->keyring_name_list);
+		write_unlock(&keyring_name_lock);
+	}
+}
+
+/*
+ * Preparse a keyring payload
+ */
+static int keyring_preparse(struct key_preparsed_payload *prep)
+{
+	return prep->datalen != 0 ? -EINVAL : 0;
+}
+
+/*
+ * Free a preparse of a user defined key payload
+ */
+static void keyring_free_preparse(struct key_preparsed_payload *prep)
+{
+}
+
+/*
+ * Initialise a keyring.
+ *
+ * Returns 0 on success, -EINVAL if given any data.
+ */
+static int keyring_instantiate(struct key *keyring,
+			       struct key_preparsed_payload *prep)
+{
+	assoc_array_init(&keyring->keys);
+	/* make the keyring available by name if it has one */
+	keyring_publish_name(keyring);
+	return 0;
+}
+
+/*
+ * Multiply 64-bits by 32-bits to 96-bits and fold back to 64-bit.  Ideally we'd
+ * fold the carry back too, but that requires inline asm.
+ */
+static u64 mult_64x32_and_fold(u64 x, u32 y)
+{
+	u64 hi = (u64)(u32)(x >> 32) * y;
+	u64 lo = (u64)(u32)(x) * y;
+	return lo + ((u64)(u32)hi << 32) + (u32)(hi >> 32);
+}
+
+/*
+ * Hash a key type and description.
+ */
+static void hash_key_type_and_desc(struct keyring_index_key *index_key)
+{
+	const unsigned level_shift = ASSOC_ARRAY_LEVEL_STEP;
+	const unsigned long fan_mask = ASSOC_ARRAY_FAN_MASK;
+	const char *description = index_key->description;
+	unsigned long hash, type;
+	u32 piece;
+	u64 acc;
+	int n, desc_len = index_key->desc_len;
+
+	type = (unsigned long)index_key->type;
+	acc = mult_64x32_and_fold(type, desc_len + 13);
+	acc = mult_64x32_and_fold(acc, 9207);
+	piece = (unsigned long)index_key->domain_tag;
+	acc = mult_64x32_and_fold(acc, piece);
+	acc = mult_64x32_and_fold(acc, 9207);
+
+	for (;;) {
+		n = desc_len;
+		if (n <= 0)
+			break;
+		if (n > 4)
+			n = 4;
+		piece = 0;
+		memcpy(&piece, description, n);
+		description += n;
+		desc_len -= n;
+		acc = mult_64x32_and_fold(acc, piece);
+		acc = mult_64x32_and_fold(acc, 9207);
+	}
+
+	/* Fold the hash down to 32 bits if need be. */
+	hash = acc;
+	if (ASSOC_ARRAY_KEY_CHUNK_SIZE == 32)
+		hash ^= acc >> 32;
+
+	/* Squidge all the keyrings into a separate part of the tree to
+	 * ordinary keys by making sure the lowest level segment in the hash is
+	 * zero for keyrings and non-zero otherwise.
+	 */
+	if (index_key->type != &key_type_keyring && (hash & fan_mask) == 0)
+		hash |= (hash >> (ASSOC_ARRAY_KEY_CHUNK_SIZE - level_shift)) | 1;
+	else if (index_key->type == &key_type_keyring && (hash & fan_mask) != 0)
+		hash = (hash + (hash << level_shift)) & ~fan_mask;
+	index_key->hash = hash;
+}
+
+/*
+ * Finalise an index key to include a part of the description actually in the
+ * index key, to set the domain tag and to calculate the hash.
+ */
+void key_set_index_key(struct keyring_index_key *index_key)
+{
+	static struct key_tag default_domain_tag = { .usage = REFCOUNT_INIT(1), };
+	size_t n = min_t(size_t, index_key->desc_len, sizeof(index_key->desc));
+
+	memcpy(index_key->desc, index_key->description, n);
+
+	if (!index_key->domain_tag) {
+		if (index_key->type->flags & KEY_TYPE_NET_DOMAIN)
+			index_key->domain_tag = current->nsproxy->net_ns->key_domain;
+		else
+			index_key->domain_tag = &default_domain_tag;
+	}
+
+	hash_key_type_and_desc(index_key);
+}
+
+/**
+ * key_put_tag - Release a ref on a tag.
+ * @tag: The tag to release.
+ *
+ * This releases a reference the given tag and returns true if that ref was the
+ * last one.
+ */
+bool key_put_tag(struct key_tag *tag)
+{
+	if (refcount_dec_and_test(&tag->usage)) {
+		kfree_rcu(tag, rcu);
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * key_remove_domain - Kill off a key domain and gc its keys
+ * @domain_tag: The domain tag to release.
+ *
+ * This marks a domain tag as being dead and releases a ref on it.  If that
+ * wasn't the last reference, the garbage collector is poked to try and delete
+ * all keys that were in the domain.
+ */
+void key_remove_domain(struct key_tag *domain_tag)
+{
+	domain_tag->removed = true;
+	if (!key_put_tag(domain_tag))
+		key_schedule_gc_links();
+}
+
+/*
+ * Build the next index key chunk.
+ *
+ * We return it one word-sized chunk at a time.
+ */
+static unsigned long keyring_get_key_chunk(const void *data, int level)
+{
+	const struct keyring_index_key *index_key = data;
+	unsigned long chunk = 0;
+	const u8 *d;
+	int desc_len = index_key->desc_len, n = sizeof(chunk);
+
+	level /= ASSOC_ARRAY_KEY_CHUNK_SIZE;
+	switch (level) {
+	case 0:
+		return index_key->hash;
+	case 1:
+		return index_key->x;
+	case 2:
+		return (unsigned long)index_key->type;
+	case 3:
+		return (unsigned long)index_key->domain_tag;
+	default:
+		level -= 4;
+		if (desc_len <= sizeof(index_key->desc))
+			return 0;
+
+		d = index_key->description + sizeof(index_key->desc);
+		d += level * sizeof(long);
+		desc_len -= sizeof(index_key->desc);
+		if (desc_len > n)
+			desc_len = n;
+		do {
+			chunk <<= 8;
+			chunk |= *d++;
+		} while (--desc_len > 0);
+		return chunk;
+	}
+}
+
+static unsigned long keyring_get_object_key_chunk(const void *object, int level)
+{
+	const struct key *key = keyring_ptr_to_key(object);
+	return keyring_get_key_chunk(&key->index_key, level);
+}
+
+static bool keyring_compare_object(const void *object, const void *data)
+{
+	const struct keyring_index_key *index_key = data;
+	const struct key *key = keyring_ptr_to_key(object);
+
+	return key->index_key.type == index_key->type &&
+		key->index_key.domain_tag == index_key->domain_tag &&
+		key->index_key.desc_len == index_key->desc_len &&
+		memcmp(key->index_key.description, index_key->description,
+		       index_key->desc_len) == 0;
+}
+
+/*
+ * Compare the index keys of a pair of objects and determine the bit position
+ * at which they differ - if they differ.
+ */
+static int keyring_diff_objects(const void *object, const void *data)
+{
+	const struct key *key_a = keyring_ptr_to_key(object);
+	const struct keyring_index_key *a = &key_a->index_key;
+	const struct keyring_index_key *b = data;
+	unsigned long seg_a, seg_b;
+	int level, i;
+
+	level = 0;
+	seg_a = a->hash;
+	seg_b = b->hash;
+	if ((seg_a ^ seg_b) != 0)
+		goto differ;
+	level += ASSOC_ARRAY_KEY_CHUNK_SIZE / 8;
+
+	/* The number of bits contributed by the hash is controlled by a
+	 * constant in the assoc_array headers.  Everything else thereafter we
+	 * can deal with as being machine word-size dependent.
+	 */
+	seg_a = a->x;
+	seg_b = b->x;
+	if ((seg_a ^ seg_b) != 0)
+		goto differ;
+	level += sizeof(unsigned long);
+
+	/* The next bit may not work on big endian */
+	seg_a = (unsigned long)a->type;
+	seg_b = (unsigned long)b->type;
+	if ((seg_a ^ seg_b) != 0)
+		goto differ;
+	level += sizeof(unsigned long);
+
+	seg_a = (unsigned long)a->domain_tag;
+	seg_b = (unsigned long)b->domain_tag;
+	if ((seg_a ^ seg_b) != 0)
+		goto differ;
+	level += sizeof(unsigned long);
+
+	i = sizeof(a->desc);
+	if (a->desc_len <= i)
+		goto same;
+
+	for (; i < a->desc_len; i++) {
+		seg_a = *(unsigned char *)(a->description + i);
+		seg_b = *(unsigned char *)(b->description + i);
+		if ((seg_a ^ seg_b) != 0)
+			goto differ_plus_i;
+	}
+
+same:
+	return -1;
+
+differ_plus_i:
+	level += i;
+differ:
+	i = level * 8 + __ffs(seg_a ^ seg_b);
+	return i;
+}
+
+/*
+ * Free an object after stripping the keyring flag off of the pointer.
+ */
+static void keyring_free_object(void *object)
+{
+	key_put(keyring_ptr_to_key(object));
+}
+
+/*
+ * Operations for keyring management by the index-tree routines.
+ */
+static const struct assoc_array_ops keyring_assoc_array_ops = {
+	.get_key_chunk		= keyring_get_key_chunk,
+	.get_object_key_chunk	= keyring_get_object_key_chunk,
+	.compare_object		= keyring_compare_object,
+	.diff_objects		= keyring_diff_objects,
+	.free_object		= keyring_free_object,
+};
+
+/*
+ * Clean up a keyring when it is destroyed.  Unpublish its name if it had one
+ * and dispose of its data.
+ *
+ * The garbage collector detects the final key_put(), removes the keyring from
+ * the serial number tree and then does RCU synchronisation before coming here,
+ * so we shouldn't need to worry about code poking around here with the RCU
+ * readlock held by this time.
+ */
+static void keyring_destroy(struct key *keyring)
+{
+	if (keyring->description) {
+		write_lock(&keyring_name_lock);
+
+		if (keyring->name_link.next != NULL &&
+		    !list_empty(&keyring->name_link))
+			list_del(&keyring->name_link);
+
+		write_unlock(&keyring_name_lock);
+	}
+
+	if (keyring->restrict_link) {
+		struct key_restriction *keyres = keyring->restrict_link;
+
+		key_put(keyres->key);
+		kfree(keyres);
+	}
+
+	assoc_array_destroy(&keyring->keys, &keyring_assoc_array_ops);
+}
+
+/*
+ * Describe a keyring for /proc.
+ */
+static void keyring_describe(const struct key *keyring, struct seq_file *m)
+{
+	if (keyring->description)
+		seq_puts(m, keyring->description);
+	else
+		seq_puts(m, "[anon]");
+
+	if (key_is_positive(keyring)) {
+		if (keyring->keys.nr_leaves_on_tree != 0)
+			seq_printf(m, ": %lu", keyring->keys.nr_leaves_on_tree);
+		else
+			seq_puts(m, ": empty");
+	}
+}
+
+struct keyring_read_iterator_context {
+	size_t			buflen;
+	size_t			count;
+	key_serial_t		*buffer;
+};
+
+static int keyring_read_iterator(const void *object, void *data)
+{
+	struct keyring_read_iterator_context *ctx = data;
+	const struct key *key = keyring_ptr_to_key(object);
+
+	kenter("{%s,%d},,{%zu/%zu}",
+	       key->type->name, key->serial, ctx->count, ctx->buflen);
+
+	if (ctx->count >= ctx->buflen)
+		return 1;
+
+	*ctx->buffer++ = key->serial;
+	ctx->count += sizeof(key->serial);
+	return 0;
+}
+
+/*
+ * Read a list of key IDs from the keyring's contents in binary form
+ *
+ * The keyring's semaphore is read-locked by the caller.  This prevents someone
+ * from modifying it under us - which could cause us to read key IDs multiple
+ * times.
+ */
+static long keyring_read(const struct key *keyring,
+			 char *buffer, size_t buflen)
+{
+	struct keyring_read_iterator_context ctx;
+	long ret;
+
+	kenter("{%d},,%zu", key_serial(keyring), buflen);
+
+	if (buflen & (sizeof(key_serial_t) - 1))
+		return -EINVAL;
+
+	/* Copy as many key IDs as fit into the buffer */
+	if (buffer && buflen) {
+		ctx.buffer = (key_serial_t *)buffer;
+		ctx.buflen = buflen;
+		ctx.count = 0;
+		ret = assoc_array_iterate(&keyring->keys,
+					  keyring_read_iterator, &ctx);
+		if (ret < 0) {
+			kleave(" = %ld [iterate]", ret);
+			return ret;
+		}
+	}
+
+	/* Return the size of the buffer needed */
+	ret = keyring->keys.nr_leaves_on_tree * sizeof(key_serial_t);
+	if (ret <= buflen)
+		kleave("= %ld [ok]", ret);
+	else
+		kleave("= %ld [buffer too small]", ret);
+	return ret;
+}
+
+/*
+ * Allocate a keyring and link into the destination keyring.
+ */
+struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
+			  const struct cred *cred, key_perm_t perm,
+			  unsigned long flags,
+			  struct key_restriction *restrict_link,
+			  struct key *dest)
+{
+	struct key *keyring;
+	int ret;
+
+	keyring = key_alloc(&key_type_keyring, description,
+			    uid, gid, cred, perm, flags, restrict_link);
+	if (!IS_ERR(keyring)) {
+		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
+		if (ret < 0) {
+			key_put(keyring);
+			keyring = ERR_PTR(ret);
+		}
+	}
+
+	return keyring;
+}
+EXPORT_SYMBOL(keyring_alloc);
+
+/**
+ * restrict_link_reject - Give -EPERM to restrict link
+ * @keyring: The keyring being added to.
+ * @type: The type of key being added.
+ * @payload: The payload of the key intended to be added.
+ * @restriction_key: Keys providing additional data for evaluating restriction.
+ *
+ * Reject the addition of any links to a keyring.  It can be overridden by
+ * passing KEY_ALLOC_BYPASS_RESTRICTION to key_instantiate_and_link() when
+ * adding a key to a keyring.
+ *
+ * This is meant to be stored in a key_restriction structure which is passed
+ * in the restrict_link parameter to keyring_alloc().
+ */
+int restrict_link_reject(struct key *keyring,
+			 const struct key_type *type,
+			 const union key_payload *payload,
+			 struct key *restriction_key)
+{
+	return -EPERM;
+}
+
+/*
+ * By default, we keys found by getting an exact match on their descriptions.
+ */
+bool key_default_cmp(const struct key *key,
+		     const struct key_match_data *match_data)
+{
+	return strcmp(key->description, match_data->raw_data) == 0;
+}
+
+/*
+ * Iteration function to consider each key found.
+ */
+static int keyring_search_iterator(const void *object, void *iterator_data)
+{
+	struct keyring_search_context *ctx = iterator_data;
+	const struct key *key = keyring_ptr_to_key(object);
+	unsigned long kflags = READ_ONCE(key->flags);
+	short state = READ_ONCE(key->state);
+
+	kenter("{%d}", key->serial);
+
+	/* ignore keys not of this type */
+	if (key->type != ctx->index_key.type) {
+		kleave(" = 0 [!type]");
+		return 0;
+	}
+
+	/* skip invalidated, revoked and expired keys */
+	if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
+		time64_t expiry = READ_ONCE(key->expiry);
+
+		if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
+			      (1 << KEY_FLAG_REVOKED))) {
+			ctx->result = ERR_PTR(-EKEYREVOKED);
+			kleave(" = %d [invrev]", ctx->skipped_ret);
+			goto skipped;
+		}
+
+		if (expiry && ctx->now >= expiry) {
+			if (!(ctx->flags & KEYRING_SEARCH_SKIP_EXPIRED))
+				ctx->result = ERR_PTR(-EKEYEXPIRED);
+			kleave(" = %d [expire]", ctx->skipped_ret);
+			goto skipped;
+		}
+	}
+
+	/* keys that don't match */
+	if (!ctx->match_data.cmp(key, &ctx->match_data)) {
+		kleave(" = 0 [!match]");
+		return 0;
+	}
+
+	/* key must have search permissions */
+	if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
+	    key_task_permission(make_key_ref(key, ctx->possessed),
+				ctx->cred, KEY_NEED_SEARCH) < 0) {
+		ctx->result = ERR_PTR(-EACCES);
+		kleave(" = %d [!perm]", ctx->skipped_ret);
+		goto skipped;
+	}
+
+	if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
+		/* we set a different error code if we pass a negative key */
+		if (state < 0) {
+			ctx->result = ERR_PTR(state);
+			kleave(" = %d [neg]", ctx->skipped_ret);
+			goto skipped;
+		}
+	}
+
+	/* Found */
+	ctx->result = make_key_ref(key, ctx->possessed);
+	kleave(" = 1 [found]");
+	return 1;
+
+skipped:
+	return ctx->skipped_ret;
+}
+
+/*
+ * Search inside a keyring for a key.  We can search by walking to it
+ * directly based on its index-key or we can iterate over the entire
+ * tree looking for it, based on the match function.
+ */
+static int search_keyring(struct key *keyring, struct keyring_search_context *ctx)
+{
+	if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_DIRECT) {
+		const void *object;
+
+		object = assoc_array_find(&keyring->keys,
+					  &keyring_assoc_array_ops,
+					  &ctx->index_key);
+		return object ? ctx->iterator(object, ctx) : 0;
+	}
+	return assoc_array_iterate(&keyring->keys, ctx->iterator, ctx);
+}
+
+/*
+ * Search a tree of keyrings that point to other keyrings up to the maximum
+ * depth.
+ */
+static bool search_nested_keyrings(struct key *keyring,
+				   struct keyring_search_context *ctx)
+{
+	struct {
+		struct key *keyring;
+		struct assoc_array_node *node;
+		int slot;
+	} stack[KEYRING_SEARCH_MAX_DEPTH];
+
+	struct assoc_array_shortcut *shortcut;
+	struct assoc_array_node *node;
+	struct assoc_array_ptr *ptr;
+	struct key *key;
+	int sp = 0, slot;
+
+	kenter("{%d},{%s,%s}",
+	       keyring->serial,
+	       ctx->index_key.type->name,
+	       ctx->index_key.description);
+
+#define STATE_CHECKS (KEYRING_SEARCH_NO_STATE_CHECK | KEYRING_SEARCH_DO_STATE_CHECK)
+	BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
+	       (ctx->flags & STATE_CHECKS) == STATE_CHECKS);
+
+	if (ctx->index_key.description)
+		key_set_index_key(&ctx->index_key);
+
+	/* Check to see if this top-level keyring is what we are looking for
+	 * and whether it is valid or not.
+	 */
+	if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_ITERATE ||
+	    keyring_compare_object(keyring, &ctx->index_key)) {
+		ctx->skipped_ret = 2;
+		switch (ctx->iterator(keyring_key_to_ptr(keyring), ctx)) {
+		case 1:
+			goto found;
+		case 2:
+			return false;
+		default:
+			break;
+		}
+	}
+
+	ctx->skipped_ret = 0;
+
+	/* Start processing a new keyring */
+descend_to_keyring:
+	kdebug("descend to %d", keyring->serial);
+	if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
+			      (1 << KEY_FLAG_REVOKED)))
+		goto not_this_keyring;
+
+	/* Search through the keys in this keyring before its searching its
+	 * subtrees.
+	 */
+	if (search_keyring(keyring, ctx))
+		goto found;
+
+	/* Then manually iterate through the keyrings nested in this one.
+	 *
+	 * Start from the root node of the index tree.  Because of the way the
+	 * hash function has been set up, keyrings cluster on the leftmost
+	 * branch of the root node (root slot 0) or in the root node itself.
+	 * Non-keyrings avoid the leftmost branch of the root entirely (root
+	 * slots 1-15).
+	 */
+	if (!(ctx->flags & KEYRING_SEARCH_RECURSE))
+		goto not_this_keyring;
+
+	ptr = READ_ONCE(keyring->keys.root);
+	if (!ptr)
+		goto not_this_keyring;
+
+	if (assoc_array_ptr_is_shortcut(ptr)) {
+		/* If the root is a shortcut, either the keyring only contains
+		 * keyring pointers (everything clusters behind root slot 0) or
+		 * doesn't contain any keyring pointers.
+		 */
+		shortcut = assoc_array_ptr_to_shortcut(ptr);
+		if ((shortcut->index_key[0] & ASSOC_ARRAY_FAN_MASK) != 0)
+			goto not_this_keyring;
+
+		ptr = READ_ONCE(shortcut->next_node);
+		node = assoc_array_ptr_to_node(ptr);
+		goto begin_node;
+	}
+
+	node = assoc_array_ptr_to_node(ptr);
+	ptr = node->slots[0];
+	if (!assoc_array_ptr_is_meta(ptr))
+		goto begin_node;
+
+descend_to_node:
+	/* Descend to a more distal node in this keyring's content tree and go
+	 * through that.
+	 */
+	kdebug("descend");
+	if (assoc_array_ptr_is_shortcut(ptr)) {
+		shortcut = assoc_array_ptr_to_shortcut(ptr);
+		ptr = READ_ONCE(shortcut->next_node);
+		BUG_ON(!assoc_array_ptr_is_node(ptr));
+	}
+	node = assoc_array_ptr_to_node(ptr);
+
+begin_node:
+	kdebug("begin_node");
+	slot = 0;
+ascend_to_node:
+	/* Go through the slots in a node */
+	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
+		ptr = READ_ONCE(node->slots[slot]);
+
+		if (assoc_array_ptr_is_meta(ptr) && node->back_pointer)
+			goto descend_to_node;
+
+		if (!keyring_ptr_is_keyring(ptr))
+			continue;
+
+		key = keyring_ptr_to_key(ptr);
+
+		if (sp >= KEYRING_SEARCH_MAX_DEPTH) {
+			if (ctx->flags & KEYRING_SEARCH_DETECT_TOO_DEEP) {
+				ctx->result = ERR_PTR(-ELOOP);
+				return false;
+			}
+			goto not_this_keyring;
+		}
+
+		/* Search a nested keyring */
+		if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
+		    key_task_permission(make_key_ref(key, ctx->possessed),
+					ctx->cred, KEY_NEED_SEARCH) < 0)
+			continue;
+
+		/* stack the current position */
+		stack[sp].keyring = keyring;
+		stack[sp].node = node;
+		stack[sp].slot = slot;
+		sp++;
+
+		/* begin again with the new keyring */
+		keyring = key;
+		goto descend_to_keyring;
+	}
+
+	/* We've dealt with all the slots in the current node, so now we need
+	 * to ascend to the parent and continue processing there.
+	 */
+	ptr = READ_ONCE(node->back_pointer);
+	slot = node->parent_slot;
+
+	if (ptr && assoc_array_ptr_is_shortcut(ptr)) {
+		shortcut = assoc_array_ptr_to_shortcut(ptr);
+		ptr = READ_ONCE(shortcut->back_pointer);
+		slot = shortcut->parent_slot;
+	}
+	if (!ptr)
+		goto not_this_keyring;
+	node = assoc_array_ptr_to_node(ptr);
+	slot++;
+
+	/* If we've ascended to the root (zero backpointer), we must have just
+	 * finished processing the leftmost branch rather than the root slots -
+	 * so there can't be any more keyrings for us to find.
+	 */
+	if (node->back_pointer) {
+		kdebug("ascend %d", slot);
+		goto ascend_to_node;
+	}
+
+	/* The keyring we're looking at was disqualified or didn't contain a
+	 * matching key.
+	 */
+not_this_keyring:
+	kdebug("not_this_keyring %d", sp);
+	if (sp <= 0) {
+		kleave(" = false");
+		return false;
+	}
+
+	/* Resume the processing of a keyring higher up in the tree */
+	sp--;
+	keyring = stack[sp].keyring;
+	node = stack[sp].node;
+	slot = stack[sp].slot + 1;
+	kdebug("ascend to %d [%d]", keyring->serial, slot);
+	goto ascend_to_node;
+
+	/* We found a viable match */
+found:
+	key = key_ref_to_ptr(ctx->result);
+	key_check(key);
+	if (!(ctx->flags & KEYRING_SEARCH_NO_UPDATE_TIME)) {
+		key->last_used_at = ctx->now;
+		keyring->last_used_at = ctx->now;
+		while (sp > 0)
+			stack[--sp].keyring->last_used_at = ctx->now;
+	}
+	kleave(" = true");
+	return true;
+}
+
+/**
+ * keyring_search_rcu - Search a keyring tree for a matching key under RCU
+ * @keyring_ref: A pointer to the keyring with possession indicator.
+ * @ctx: The keyring search context.
+ *
+ * Search the supplied keyring tree for a key that matches the criteria given.
+ * The root keyring and any linked keyrings must grant Search permission to the
+ * caller to be searchable and keys can only be found if they too grant Search
+ * to the caller. The possession flag on the root keyring pointer controls use
+ * of the possessor bits in permissions checking of the entire tree.  In
+ * addition, the LSM gets to forbid keyring searches and key matches.
+ *
+ * The search is performed as a breadth-then-depth search up to the prescribed
+ * limit (KEYRING_SEARCH_MAX_DEPTH).  The caller must hold the RCU read lock to
+ * prevent keyrings from being destroyed or rearranged whilst they are being
+ * searched.
+ *
+ * Keys are matched to the type provided and are then filtered by the match
+ * function, which is given the description to use in any way it sees fit.  The
+ * match function may use any attributes of a key that it wishes to
+ * determine the match.  Normally the match function from the key type would be
+ * used.
+ *
+ * RCU can be used to prevent the keyring key lists from disappearing without
+ * the need to take lots of locks.
+ *
+ * Returns a pointer to the found key and increments the key usage count if
+ * successful; -EAGAIN if no matching keys were found, or if expired or revoked
+ * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
+ * specified keyring wasn't a keyring.
+ *
+ * In the case of a successful return, the possession attribute from
+ * @keyring_ref is propagated to the returned key reference.
+ */
+key_ref_t keyring_search_rcu(key_ref_t keyring_ref,
+			     struct keyring_search_context *ctx)
+{
+	struct key *keyring;
+	long err;
+
+	ctx->iterator = keyring_search_iterator;
+	ctx->possessed = is_key_possessed(keyring_ref);
+	ctx->result = ERR_PTR(-EAGAIN);
+
+	keyring = key_ref_to_ptr(keyring_ref);
+	key_check(keyring);
+
+	if (keyring->type != &key_type_keyring)
+		return ERR_PTR(-ENOTDIR);
+
+	if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM)) {
+		err = key_task_permission(keyring_ref, ctx->cred, KEY_NEED_SEARCH);
+		if (err < 0)
+			return ERR_PTR(err);
+	}
+
+	ctx->now = ktime_get_real_seconds();
+	if (search_nested_keyrings(keyring, ctx))
+		__key_get(key_ref_to_ptr(ctx->result));
+	return ctx->result;
+}
+
+/**
+ * keyring_search - Search the supplied keyring tree for a matching key
+ * @keyring: The root of the keyring tree to be searched.
+ * @type: The type of keyring we want to find.
+ * @description: The name of the keyring we want to find.
+ * @recurse: True to search the children of @keyring also
+ *
+ * As keyring_search_rcu() above, but using the current task's credentials and
+ * type's default matching function and preferred search method.
+ */
+key_ref_t keyring_search(key_ref_t keyring,
+			 struct key_type *type,
+			 const char *description,
+			 bool recurse)
+{
+	struct keyring_search_context ctx = {
+		.index_key.type		= type,
+		.index_key.description	= description,
+		.index_key.desc_len	= strlen(description),
+		.cred			= current_cred(),
+		.match_data.cmp		= key_default_cmp,
+		.match_data.raw_data	= description,
+		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
+		.flags			= KEYRING_SEARCH_DO_STATE_CHECK,
+	};
+	key_ref_t key;
+	int ret;
+
+	if (recurse)
+		ctx.flags |= KEYRING_SEARCH_RECURSE;
+	if (type->match_preparse) {
+		ret = type->match_preparse(&ctx.match_data);
+		if (ret < 0)
+			return ERR_PTR(ret);
+	}
+
+	rcu_read_lock();
+	key = keyring_search_rcu(keyring, &ctx);
+	rcu_read_unlock();
+
+	if (type->match_free)
+		type->match_free(&ctx.match_data);
+	return key;
+}
+EXPORT_SYMBOL(keyring_search);
+
+static struct key_restriction *keyring_restriction_alloc(
+	key_restrict_link_func_t check)
+{
+	struct key_restriction *keyres =
+		kzalloc(sizeof(struct key_restriction), GFP_KERNEL);
+
+	if (!keyres)
+		return ERR_PTR(-ENOMEM);
+
+	keyres->check = check;
+
+	return keyres;
+}
+
+/*
+ * Semaphore to serialise restriction setup to prevent reference count
+ * cycles through restriction key pointers.
+ */
+static DECLARE_RWSEM(keyring_serialise_restrict_sem);
+
+/*
+ * Check for restriction cycles that would prevent keyring garbage collection.
+ * keyring_serialise_restrict_sem must be held.
+ */
+static bool keyring_detect_restriction_cycle(const struct key *dest_keyring,
+					     struct key_restriction *keyres)
+{
+	while (keyres && keyres->key &&
+	       keyres->key->type == &key_type_keyring) {
+		if (keyres->key == dest_keyring)
+			return true;
+
+		keyres = keyres->key->restrict_link;
+	}
+
+	return false;
+}
+
+/**
+ * keyring_restrict - Look up and apply a restriction to a keyring
+ * @keyring_ref: The keyring to be restricted
+ * @type: The key type that will provide the restriction checker.
+ * @restriction: The restriction options to apply to the keyring
+ *
+ * Look up a keyring and apply a restriction to it.  The restriction is managed
+ * by the specific key type, but can be configured by the options specified in
+ * the restriction string.
+ */
+int keyring_restrict(key_ref_t keyring_ref, const char *type,
+		     const char *restriction)
+{
+	struct key *keyring;
+	struct key_type *restrict_type = NULL;
+	struct key_restriction *restrict_link;
+	int ret = 0;
+
+	keyring = key_ref_to_ptr(keyring_ref);
+	key_check(keyring);
+
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	if (!type) {
+		restrict_link = keyring_restriction_alloc(restrict_link_reject);
+	} else {
+		restrict_type = key_type_lookup(type);
+
+		if (IS_ERR(restrict_type))
+			return PTR_ERR(restrict_type);
+
+		if (!restrict_type->lookup_restriction) {
+			ret = -ENOENT;
+			goto error;
+		}
+
+		restrict_link = restrict_type->lookup_restriction(restriction);
+	}
+
+	if (IS_ERR(restrict_link)) {
+		ret = PTR_ERR(restrict_link);
+		goto error;
+	}
+
+	down_write(&keyring->sem);
+	down_write(&keyring_serialise_restrict_sem);
+
+	if (keyring->restrict_link) {
+		ret = -EEXIST;
+	} else if (keyring_detect_restriction_cycle(keyring, restrict_link)) {
+		ret = -EDEADLK;
+	} else {
+		keyring->restrict_link = restrict_link;
+		notify_key(keyring, NOTIFY_KEY_SETATTR, 0);
+	}
+
+	up_write(&keyring_serialise_restrict_sem);
+	up_write(&keyring->sem);
+
+	if (ret < 0) {
+		key_put(restrict_link->key);
+		kfree(restrict_link);
+	}
+
+error:
+	if (restrict_type)
+		key_type_put(restrict_type);
+
+	return ret;
+}
+EXPORT_SYMBOL(keyring_restrict);
+
+/*
+ * Search the given keyring for a key that might be updated.
+ *
+ * The caller must guarantee that the keyring is a keyring and that the
+ * permission is granted to modify the keyring as no check is made here.  The
+ * caller must also hold a lock on the keyring semaphore.
+ *
+ * Returns a pointer to the found key with usage count incremented if
+ * successful and returns NULL if not found.  Revoked and invalidated keys are
+ * skipped over.
+ *
+ * If successful, the possession indicator is propagated from the keyring ref
+ * to the returned key reference.
+ */
+key_ref_t find_key_to_update(key_ref_t keyring_ref,
+			     const struct keyring_index_key *index_key)
+{
+	struct key *keyring, *key;
+	const void *object;
+
+	keyring = key_ref_to_ptr(keyring_ref);
+
+	kenter("{%d},{%s,%s}",
+	       keyring->serial, index_key->type->name, index_key->description);
+
+	object = assoc_array_find(&keyring->keys, &keyring_assoc_array_ops,
+				  index_key);
+
+	if (object)
+		goto found;
+
+	kleave(" = NULL");
+	return NULL;
+
+found:
+	key = keyring_ptr_to_key(object);
+	if (key->flags & ((1 << KEY_FLAG_INVALIDATED) |
+			  (1 << KEY_FLAG_REVOKED))) {
+		kleave(" = NULL [x]");
+		return NULL;
+	}
+	__key_get(key);
+	kleave(" = {%d}", key->serial);
+	return make_key_ref(key, is_key_possessed(keyring_ref));
+}
+
+/*
+ * Find a keyring with the specified name.
+ *
+ * Only keyrings that have nonzero refcount, are not revoked, and are owned by a
+ * user in the current user namespace are considered.  If @uid_keyring is %true,
+ * the keyring additionally must have been allocated as a user or user session
+ * keyring; otherwise, it must grant Search permission directly to the caller.
+ *
+ * Returns a pointer to the keyring with the keyring's refcount having being
+ * incremented on success.  -ENOKEY is returned if a key could not be found.
+ */
+struct key *find_keyring_by_name(const char *name, bool uid_keyring)
+{
+	struct user_namespace *ns = current_user_ns();
+	struct key *keyring;
+
+	if (!name)
+		return ERR_PTR(-EINVAL);
+
+	read_lock(&keyring_name_lock);
+
+	/* Search this hash bucket for a keyring with a matching name that
+	 * grants Search permission and that hasn't been revoked
+	 */
+	list_for_each_entry(keyring, &ns->keyring_name_list, name_link) {
+		if (!kuid_has_mapping(ns, keyring->user->uid))
+			continue;
+
+		if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
+			continue;
+
+		if (strcmp(keyring->description, name) != 0)
+			continue;
+
+		if (uid_keyring) {
+			if (!test_bit(KEY_FLAG_UID_KEYRING,
+				      &keyring->flags))
+				continue;
+		} else {
+			if (key_permission(make_key_ref(keyring, 0),
+					   KEY_NEED_SEARCH) < 0)
+				continue;
+		}
+
+		/* we've got a match but we might end up racing with
+		 * key_cleanup() if the keyring is currently 'dead'
+		 * (ie. it has a zero usage count) */
+		if (!refcount_inc_not_zero(&keyring->usage))
+			continue;
+		keyring->last_used_at = ktime_get_real_seconds();
+		goto out;
+	}
+
+	keyring = ERR_PTR(-ENOKEY);
+out:
+	read_unlock(&keyring_name_lock);
+	return keyring;
+}
+
+static int keyring_detect_cycle_iterator(const void *object,
+					 void *iterator_data)
+{
+	struct keyring_search_context *ctx = iterator_data;
+	const struct key *key = keyring_ptr_to_key(object);
+
+	kenter("{%d}", key->serial);
+
+	/* We might get a keyring with matching index-key that is nonetheless a
+	 * different keyring. */
+	if (key != ctx->match_data.raw_data)
+		return 0;
+
+	ctx->result = ERR_PTR(-EDEADLK);
+	return 1;
+}
+
+/*
+ * See if a cycle will be created by inserting acyclic tree B in acyclic
+ * tree A at the topmost level (ie: as a direct child of A).
+ *
+ * Since we are adding B to A at the top level, checking for cycles should just
+ * be a matter of seeing if node A is somewhere in tree B.
+ */
+static int keyring_detect_cycle(struct key *A, struct key *B)
+{
+	struct keyring_search_context ctx = {
+		.index_key		= A->index_key,
+		.match_data.raw_data	= A,
+		.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
+		.iterator		= keyring_detect_cycle_iterator,
+		.flags			= (KEYRING_SEARCH_NO_STATE_CHECK |
+					   KEYRING_SEARCH_NO_UPDATE_TIME |
+					   KEYRING_SEARCH_NO_CHECK_PERM |
+					   KEYRING_SEARCH_DETECT_TOO_DEEP |
+					   KEYRING_SEARCH_RECURSE),
+	};
+
+	rcu_read_lock();
+	search_nested_keyrings(B, &ctx);
+	rcu_read_unlock();
+	return PTR_ERR(ctx.result) == -EAGAIN ? 0 : PTR_ERR(ctx.result);
+}
+
+/*
+ * Lock keyring for link.
+ */
+int __key_link_lock(struct key *keyring,
+		    const struct keyring_index_key *index_key)
+	__acquires(&keyring->sem)
+	__acquires(&keyring_serialise_link_lock)
+{
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	down_write(&keyring->sem);
+
+	/* Serialise link/link calls to prevent parallel calls causing a cycle
+	 * when linking two keyring in opposite orders.
+	 */
+	if (index_key->type == &key_type_keyring)
+		mutex_lock(&keyring_serialise_link_lock);
+
+	return 0;
+}
+
+/*
+ * Lock keyrings for move (link/unlink combination).
+ */
+int __key_move_lock(struct key *l_keyring, struct key *u_keyring,
+		    const struct keyring_index_key *index_key)
+	__acquires(&l_keyring->sem)
+	__acquires(&u_keyring->sem)
+	__acquires(&keyring_serialise_link_lock)
+{
+	if (l_keyring->type != &key_type_keyring ||
+	    u_keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	/* We have to be very careful here to take the keyring locks in the
+	 * right order, lest we open ourselves to deadlocking against another
+	 * move operation.
+	 */
+	if (l_keyring < u_keyring) {
+		down_write(&l_keyring->sem);
+		down_write_nested(&u_keyring->sem, 1);
+	} else {
+		down_write(&u_keyring->sem);
+		down_write_nested(&l_keyring->sem, 1);
+	}
+
+	/* Serialise link/link calls to prevent parallel calls causing a cycle
+	 * when linking two keyring in opposite orders.
+	 */
+	if (index_key->type == &key_type_keyring)
+		mutex_lock(&keyring_serialise_link_lock);
+
+	return 0;
+}
+
+/*
+ * Preallocate memory so that a key can be linked into to a keyring.
+ */
+int __key_link_begin(struct key *keyring,
+		     const struct keyring_index_key *index_key,
+		     struct assoc_array_edit **_edit)
+{
+	struct assoc_array_edit *edit;
+	int ret;
+
+	kenter("%d,%s,%s,",
+	       keyring->serial, index_key->type->name, index_key->description);
+
+	BUG_ON(index_key->desc_len == 0);
+	BUG_ON(*_edit != NULL);
+
+	*_edit = NULL;
+
+	ret = -EKEYREVOKED;
+	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
+		goto error;
+
+	/* Create an edit script that will insert/replace the key in the
+	 * keyring tree.
+	 */
+	edit = assoc_array_insert(&keyring->keys,
+				  &keyring_assoc_array_ops,
+				  index_key,
+				  NULL);
+	if (IS_ERR(edit)) {
+		ret = PTR_ERR(edit);
+		goto error;
+	}
+
+	/* If we're not replacing a link in-place then we're going to need some
+	 * extra quota.
+	 */
+	if (!edit->dead_leaf) {
+		ret = key_payload_reserve(keyring,
+					  keyring->datalen + KEYQUOTA_LINK_BYTES);
+		if (ret < 0)
+			goto error_cancel;
+	}
+
+	*_edit = edit;
+	kleave(" = 0");
+	return 0;
+
+error_cancel:
+	assoc_array_cancel_edit(edit);
+error:
+	kleave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * Check already instantiated keys aren't going to be a problem.
+ *
+ * The caller must have called __key_link_begin(). Don't need to call this for
+ * keys that were created since __key_link_begin() was called.
+ */
+int __key_link_check_live_key(struct key *keyring, struct key *key)
+{
+	if (key->type == &key_type_keyring)
+		/* check that we aren't going to create a cycle by linking one
+		 * keyring to another */
+		return keyring_detect_cycle(keyring, key);
+	return 0;
+}
+
+/*
+ * Link a key into to a keyring.
+ *
+ * Must be called with __key_link_begin() having being called.  Discards any
+ * already extant link to matching key if there is one, so that each keyring
+ * holds at most one link to any given key of a particular type+description
+ * combination.
+ */
+void __key_link(struct key *keyring, struct key *key,
+		struct assoc_array_edit **_edit)
+{
+	__key_get(key);
+	assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
+	assoc_array_apply_edit(*_edit);
+	*_edit = NULL;
+	notify_key(keyring, NOTIFY_KEY_LINKED, key_serial(key));
+}
+
+/*
+ * Finish linking a key into to a keyring.
+ *
+ * Must be called with __key_link_begin() having being called.
+ */
+void __key_link_end(struct key *keyring,
+		    const struct keyring_index_key *index_key,
+		    struct assoc_array_edit *edit)
+	__releases(&keyring->sem)
+	__releases(&keyring_serialise_link_lock)
+{
+	BUG_ON(index_key->type == NULL);
+	kenter("%d,%s,", keyring->serial, index_key->type->name);
+
+	if (edit) {
+		if (!edit->dead_leaf) {
+			key_payload_reserve(keyring,
+				keyring->datalen - KEYQUOTA_LINK_BYTES);
+		}
+		assoc_array_cancel_edit(edit);
+	}
+	up_write(&keyring->sem);
+
+	if (index_key->type == &key_type_keyring)
+		mutex_unlock(&keyring_serialise_link_lock);
+}
+
+/*
+ * Check addition of keys to restricted keyrings.
+ */
+static int __key_link_check_restriction(struct key *keyring, struct key *key)
+{
+	if (!keyring->restrict_link || !keyring->restrict_link->check)
+		return 0;
+	return keyring->restrict_link->check(keyring, key->type, &key->payload,
+					     keyring->restrict_link->key);
+}
+
+/**
+ * key_link - Link a key to a keyring
+ * @keyring: The keyring to make the link in.
+ * @key: The key to link to.
+ *
+ * Make a link in a keyring to a key, such that the keyring holds a reference
+ * on that key and the key can potentially be found by searching that keyring.
+ *
+ * This function will write-lock the keyring's semaphore and will consume some
+ * of the user's key data quota to hold the link.
+ *
+ * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring,
+ * -EKEYREVOKED if the keyring has been revoked, -ENFILE if the keyring is
+ * full, -EDQUOT if there is insufficient key data quota remaining to add
+ * another link or -ENOMEM if there's insufficient memory.
+ *
+ * It is assumed that the caller has checked that it is permitted for a link to
+ * be made (the keyring should have Write permission and the key Link
+ * permission).
+ */
+int key_link(struct key *keyring, struct key *key)
+{
+	struct assoc_array_edit *edit = NULL;
+	int ret;
+
+	kenter("{%d,%d}", keyring->serial, refcount_read(&keyring->usage));
+
+	key_check(keyring);
+	key_check(key);
+
+	ret = __key_link_lock(keyring, &key->index_key);
+	if (ret < 0)
+		goto error;
+
+	ret = __key_link_begin(keyring, &key->index_key, &edit);
+	if (ret < 0)
+		goto error_end;
+
+	kdebug("begun {%d,%d}", keyring->serial, refcount_read(&keyring->usage));
+	ret = __key_link_check_restriction(keyring, key);
+	if (ret == 0)
+		ret = __key_link_check_live_key(keyring, key);
+	if (ret == 0)
+		__key_link(keyring, key, &edit);
+
+error_end:
+	__key_link_end(keyring, &key->index_key, edit);
+error:
+	kleave(" = %d {%d,%d}", ret, keyring->serial, refcount_read(&keyring->usage));
+	return ret;
+}
+EXPORT_SYMBOL(key_link);
+
+/*
+ * Lock a keyring for unlink.
+ */
+static int __key_unlink_lock(struct key *keyring)
+	__acquires(&keyring->sem)
+{
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	down_write(&keyring->sem);
+	return 0;
+}
+
+/*
+ * Begin the process of unlinking a key from a keyring.
+ */
+static int __key_unlink_begin(struct key *keyring, struct key *key,
+			      struct assoc_array_edit **_edit)
+{
+	struct assoc_array_edit *edit;
+
+	BUG_ON(*_edit != NULL);
+
+	edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
+				  &key->index_key);
+	if (IS_ERR(edit))
+		return PTR_ERR(edit);
+
+	if (!edit)
+		return -ENOENT;
+
+	*_edit = edit;
+	return 0;
+}
+
+/*
+ * Apply an unlink change.
+ */
+static void __key_unlink(struct key *keyring, struct key *key,
+			 struct assoc_array_edit **_edit)
+{
+	assoc_array_apply_edit(*_edit);
+	notify_key(keyring, NOTIFY_KEY_UNLINKED, key_serial(key));
+	*_edit = NULL;
+	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
+}
+
+/*
+ * Finish unlinking a key from to a keyring.
+ */
+static void __key_unlink_end(struct key *keyring,
+			     struct key *key,
+			     struct assoc_array_edit *edit)
+	__releases(&keyring->sem)
+{
+	if (edit)
+		assoc_array_cancel_edit(edit);
+	up_write(&keyring->sem);
+}
+
+/**
+ * key_unlink - Unlink the first link to a key from a keyring.
+ * @keyring: The keyring to remove the link from.
+ * @key: The key the link is to.
+ *
+ * Remove a link from a keyring to a key.
+ *
+ * This function will write-lock the keyring's semaphore.
+ *
+ * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring, -ENOENT if
+ * the key isn't linked to by the keyring or -ENOMEM if there's insufficient
+ * memory.
+ *
+ * It is assumed that the caller has checked that it is permitted for a link to
+ * be removed (the keyring should have Write permission; no permissions are
+ * required on the key).
+ */
+int key_unlink(struct key *keyring, struct key *key)
+{
+	struct assoc_array_edit *edit = NULL;
+	int ret;
+
+	key_check(keyring);
+	key_check(key);
+
+	ret = __key_unlink_lock(keyring);
+	if (ret < 0)
+		return ret;
+
+	ret = __key_unlink_begin(keyring, key, &edit);
+	if (ret == 0)
+		__key_unlink(keyring, key, &edit);
+	__key_unlink_end(keyring, key, edit);
+	return ret;
+}
+EXPORT_SYMBOL(key_unlink);
+
+/**
+ * key_move - Move a key from one keyring to another
+ * @key: The key to move
+ * @from_keyring: The keyring to remove the link from.
+ * @to_keyring: The keyring to make the link in.
+ * @flags: Qualifying flags, such as KEYCTL_MOVE_EXCL.
+ *
+ * Make a link in @to_keyring to a key, such that the keyring holds a reference
+ * on that key and the key can potentially be found by searching that keyring
+ * whilst simultaneously removing a link to the key from @from_keyring.
+ *
+ * This function will write-lock both keyring's semaphores and will consume
+ * some of the user's key data quota to hold the link on @to_keyring.
+ *
+ * Returns 0 if successful, -ENOTDIR if either keyring isn't a keyring,
+ * -EKEYREVOKED if either keyring has been revoked, -ENFILE if the second
+ * keyring is full, -EDQUOT if there is insufficient key data quota remaining
+ * to add another link or -ENOMEM if there's insufficient memory.  If
+ * KEYCTL_MOVE_EXCL is set, then -EEXIST will be returned if there's already a
+ * matching key in @to_keyring.
+ *
+ * It is assumed that the caller has checked that it is permitted for a link to
+ * be made (the keyring should have Write permission and the key Link
+ * permission).
+ */
+int key_move(struct key *key,
+	     struct key *from_keyring,
+	     struct key *to_keyring,
+	     unsigned int flags)
+{
+	struct assoc_array_edit *from_edit = NULL, *to_edit = NULL;
+	int ret;
+
+	kenter("%d,%d,%d", key->serial, from_keyring->serial, to_keyring->serial);
+
+	if (from_keyring == to_keyring)
+		return 0;
+
+	key_check(key);
+	key_check(from_keyring);
+	key_check(to_keyring);
+
+	ret = __key_move_lock(from_keyring, to_keyring, &key->index_key);
+	if (ret < 0)
+		goto out;
+	ret = __key_unlink_begin(from_keyring, key, &from_edit);
+	if (ret < 0)
+		goto error;
+	ret = __key_link_begin(to_keyring, &key->index_key, &to_edit);
+	if (ret < 0)
+		goto error;
+
+	ret = -EEXIST;
+	if (to_edit->dead_leaf && (flags & KEYCTL_MOVE_EXCL))
+		goto error;
+
+	ret = __key_link_check_restriction(to_keyring, key);
+	if (ret < 0)
+		goto error;
+	ret = __key_link_check_live_key(to_keyring, key);
+	if (ret < 0)
+		goto error;
+
+	__key_unlink(from_keyring, key, &from_edit);
+	__key_link(to_keyring, key, &to_edit);
+error:
+	__key_link_end(to_keyring, &key->index_key, to_edit);
+	__key_unlink_end(from_keyring, key, from_edit);
+out:
+	kleave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(key_move);
+
+/**
+ * keyring_clear - Clear a keyring
+ * @keyring: The keyring to clear.
+ *
+ * Clear the contents of the specified keyring.
+ *
+ * Returns 0 if successful or -ENOTDIR if the keyring isn't a keyring.
+ */
+int keyring_clear(struct key *keyring)
+{
+	struct assoc_array_edit *edit;
+	int ret;
+
+	if (keyring->type != &key_type_keyring)
+		return -ENOTDIR;
+
+	down_write(&keyring->sem);
+
+	edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
+	if (IS_ERR(edit)) {
+		ret = PTR_ERR(edit);
+	} else {
+		if (edit)
+			assoc_array_apply_edit(edit);
+		notify_key(keyring, NOTIFY_KEY_CLEARED, 0);
+		key_payload_reserve(keyring, 0);
+		ret = 0;
+	}
+
+	up_write(&keyring->sem);
+	return ret;
+}
+EXPORT_SYMBOL(keyring_clear);
+
+/*
+ * Dispose of the links from a revoked keyring.
+ *
+ * This is called with the key sem write-locked.
+ */
+static void keyring_revoke(struct key *keyring)
+{
+	struct assoc_array_edit *edit;
+
+	edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
+	if (!IS_ERR(edit)) {
+		if (edit)
+			assoc_array_apply_edit(edit);
+		key_payload_reserve(keyring, 0);
+	}
+}
+
+static bool keyring_gc_select_iterator(void *object, void *iterator_data)
+{
+	struct key *key = keyring_ptr_to_key(object);
+	time64_t *limit = iterator_data;
+
+	if (key_is_dead(key, *limit))
+		return false;
+	key_get(key);
+	return true;
+}
+
+static int keyring_gc_check_iterator(const void *object, void *iterator_data)
+{
+	const struct key *key = keyring_ptr_to_key(object);
+	time64_t *limit = iterator_data;
+
+	key_check(key);
+	return key_is_dead(key, *limit);
+}
+
+/*
+ * Garbage collect pointers from a keyring.
+ *
+ * Not called with any locks held.  The keyring's key struct will not be
+ * deallocated under us as only our caller may deallocate it.
+ */
+void keyring_gc(struct key *keyring, time64_t limit)
+{
+	int result;
+
+	kenter("%x{%s}", keyring->serial, keyring->description ?: "");
+
+	if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
+			      (1 << KEY_FLAG_REVOKED)))
+		goto dont_gc;
+
+	/* scan the keyring looking for dead keys */
+	rcu_read_lock();
+	result = assoc_array_iterate(&keyring->keys,
+				     keyring_gc_check_iterator, &limit);
+	rcu_read_unlock();
+	if (result == true)
+		goto do_gc;
+
+dont_gc:
+	kleave(" [no gc]");
+	return;
+
+do_gc:
+	down_write(&keyring->sem);
+	assoc_array_gc(&keyring->keys, &keyring_assoc_array_ops,
+		       keyring_gc_select_iterator, &limit);
+	up_write(&keyring->sem);
+	kleave(" [gc]");
+}
+
+/*
+ * Garbage collect restriction pointers from a keyring.
+ *
+ * Keyring restrictions are associated with a key type, and must be cleaned
+ * up if the key type is unregistered. The restriction is altered to always
+ * reject additional keys so a keyring cannot be opened up by unregistering
+ * a key type.
+ *
+ * Not called with any keyring locks held. The keyring's key struct will not
+ * be deallocated under us as only our caller may deallocate it.
+ *
+ * The caller is required to hold key_types_sem and dead_type->sem. This is
+ * fulfilled by key_gc_keytype() holding the locks on behalf of
+ * key_garbage_collector(), which it invokes on a workqueue.
+ */
+void keyring_restriction_gc(struct key *keyring, struct key_type *dead_type)
+{
+	struct key_restriction *keyres;
+
+	kenter("%x{%s}", keyring->serial, keyring->description ?: "");
+
+	/*
+	 * keyring->restrict_link is only assigned at key allocation time
+	 * or with the key type locked, so the only values that could be
+	 * concurrently assigned to keyring->restrict_link are for key
+	 * types other than dead_type. Given this, it's ok to check
+	 * the key type before acquiring keyring->sem.
+	 */
+	if (!dead_type || !keyring->restrict_link ||
+	    keyring->restrict_link->keytype != dead_type) {
+		kleave(" [no restriction gc]");
+		return;
+	}
+
+	/* Lock the keyring to ensure that a link is not in progress */
+	down_write(&keyring->sem);
+
+	keyres = keyring->restrict_link;
+
+	keyres->check = restrict_link_reject;
+
+	key_put(keyres->key);
+	keyres->key = NULL;
+	keyres->keytype = NULL;
+
+	up_write(&keyring->sem);
+
+	kleave(" [restriction gc]");
+}