1 files changed, 417 insertions, 0 deletions

diff --git a/fs/verity/open.c b/fs/verity/open.c
new file mode 100644
index 0000000000..6c31a871b8
--- /dev/null
+++ b/fs/verity/open.c
@@ -0,0 +1,417 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Opening fs-verity files
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+static struct kmem_cache *fsverity_info_cachep;
+
+/**
+ * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
+ * @params: the parameters struct to initialize
+ * @inode: the inode for which the Merkle tree is being built
+ * @hash_algorithm: number of hash algorithm to use
+ * @log_blocksize: log base 2 of block size to use
+ * @salt: pointer to salt (optional)
+ * @salt_size: size of salt, possibly 0
+ *
+ * Validate the hash algorithm and block size, then compute the tree topology
+ * (num levels, num blocks in each level, etc.) and initialize @params.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+				     const struct inode *inode,
+				     unsigned int hash_algorithm,
+				     unsigned int log_blocksize,
+				     const u8 *salt, size_t salt_size)
+{
+	const struct fsverity_hash_alg *hash_alg;
+	int err;
+	u64 blocks;
+	u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
+	u64 offset;
+	int level;
+
+	memset(params, 0, sizeof(*params));
+
+	hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
+	if (IS_ERR(hash_alg))
+		return PTR_ERR(hash_alg);
+	params->hash_alg = hash_alg;
+	params->digest_size = hash_alg->digest_size;
+
+	params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
+							salt_size);
+	if (IS_ERR(params->hashstate)) {
+		err = PTR_ERR(params->hashstate);
+		params->hashstate = NULL;
+		fsverity_err(inode, "Error %d preparing hash state", err);
+		goto out_err;
+	}
+
+	/*
+	 * fs/verity/ directly assumes that the Merkle tree block size is a
+	 * power of 2 less than or equal to PAGE_SIZE.  Another restriction
+	 * arises from the interaction between fs/verity/ and the filesystems
+	 * themselves: filesystems expect to be able to verify a single
+	 * filesystem block of data at a time.  Therefore, the Merkle tree block
+	 * size must also be less than or equal to the filesystem block size.
+	 *
+	 * The above are the only hard limitations, so in theory the Merkle tree
+	 * block size could be as small as twice the digest size.  However,
+	 * that's not useful, and it would result in some unusually deep and
+	 * large Merkle trees.  So we currently require that the Merkle tree
+	 * block size be at least 1024 bytes.  That's small enough to test the
+	 * sub-page block case on systems with 4K pages, but not too small.
+	 */
+	if (log_blocksize < 10 || log_blocksize > PAGE_SHIFT ||
+	    log_blocksize > inode->i_blkbits) {
+		fsverity_warn(inode, "Unsupported log_blocksize: %u",
+			      log_blocksize);
+		err = -EINVAL;
+		goto out_err;
+	}
+	params->log_blocksize = log_blocksize;
+	params->block_size = 1 << log_blocksize;
+	params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
+	params->blocks_per_page = 1 << params->log_blocks_per_page;
+
+	if (WARN_ON_ONCE(!is_power_of_2(params->digest_size))) {
+		err = -EINVAL;
+		goto out_err;
+	}
+	if (params->block_size < 2 * params->digest_size) {
+		fsverity_warn(inode,
+			      "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
+			      params->block_size, hash_alg->name);
+		err = -EINVAL;
+		goto out_err;
+	}
+	params->log_digestsize = ilog2(params->digest_size);
+	params->log_arity = log_blocksize - params->log_digestsize;
+	params->hashes_per_block = 1 << params->log_arity;
+
+	/*
+	 * Compute the number of levels in the Merkle tree and create a map from
+	 * level to the starting block of that level.  Level 'num_levels - 1' is
+	 * the root and is stored first.  Level 0 is the level directly "above"
+	 * the data blocks and is stored last.
+	 */
+
+	/* Compute number of levels and the number of blocks in each level */
+	blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
+	while (blocks > 1) {
+		if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
+			fsverity_err(inode, "Too many levels in Merkle tree");
+			err = -EFBIG;
+			goto out_err;
+		}
+		blocks = (blocks + params->hashes_per_block - 1) >>
+			 params->log_arity;
+		blocks_in_level[params->num_levels++] = blocks;
+	}
+
+	/* Compute the starting block of each level */
+	offset = 0;
+	for (level = (int)params->num_levels - 1; level >= 0; level--) {
+		params->level_start[level] = offset;
+		offset += blocks_in_level[level];
+	}
+
+	/*
+	 * With block_size != PAGE_SIZE, an in-memory bitmap will need to be
+	 * allocated to track the "verified" status of hash blocks.  Don't allow
+	 * this bitmap to get too large.  For now, limit it to 1 MiB, which
+	 * limits the file size to about 4.4 TB with SHA-256 and 4K blocks.
+	 *
+	 * Together with the fact that the data, and thus also the Merkle tree,
+	 * cannot have more than ULONG_MAX pages, this implies that hash block
+	 * indices can always fit in an 'unsigned long'.  But to be safe, we
+	 * explicitly check for that too.  Note, this is only for hash block
+	 * indices; data block indices might not fit in an 'unsigned long'.
+	 */
+	if ((params->block_size != PAGE_SIZE && offset > 1 << 23) ||
+	    offset > ULONG_MAX) {
+		fsverity_err(inode, "Too many blocks in Merkle tree");
+		err = -EFBIG;
+		goto out_err;
+	}
+
+	params->tree_size = offset << log_blocksize;
+	params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT;
+	return 0;
+
+out_err:
+	kfree(params->hashstate);
+	memset(params, 0, sizeof(*params));
+	return err;
+}
+
+/*
+ * Compute the file digest by hashing the fsverity_descriptor excluding the
+ * builtin signature and with the sig_size field set to 0.
+ */
+static int compute_file_digest(const struct fsverity_hash_alg *hash_alg,
+			       struct fsverity_descriptor *desc,
+			       u8 *file_digest)
+{
+	__le32 sig_size = desc->sig_size;
+	int err;
+
+	desc->sig_size = 0;
+	err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
+	desc->sig_size = sig_size;
+
+	return err;
+}
+
+/*
+ * Create a new fsverity_info from the given fsverity_descriptor (with optional
+ * appended builtin signature), and check the signature if present.  The
+ * fsverity_descriptor must have already undergone basic validation.
+ */
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+					   struct fsverity_descriptor *desc)
+{
+	struct fsverity_info *vi;
+	int err;
+
+	vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
+	if (!vi)
+		return ERR_PTR(-ENOMEM);
+	vi->inode = inode;
+
+	err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
+					       desc->hash_algorithm,
+					       desc->log_blocksize,
+					       desc->salt, desc->salt_size);
+	if (err) {
+		fsverity_err(inode,
+			     "Error %d initializing Merkle tree parameters",
+			     err);
+		goto fail;
+	}
+
+	memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
+
+	err = compute_file_digest(vi->tree_params.hash_alg, desc,
+				  vi->file_digest);
+	if (err) {
+		fsverity_err(inode, "Error %d computing file digest", err);
+		goto fail;
+	}
+
+	err = fsverity_verify_signature(vi, desc->signature,
+					le32_to_cpu(desc->sig_size));
+	if (err)
+		goto fail;
+
+	if (vi->tree_params.block_size != PAGE_SIZE) {
+		/*
+		 * When the Merkle tree block size and page size differ, we use
+		 * a bitmap to keep track of which hash blocks have been
+		 * verified.  This bitmap must contain one bit per hash block,
+		 * including alignment to a page boundary at the end.
+		 *
+		 * Eventually, to support extremely large files in an efficient
+		 * way, it might be necessary to make pages of this bitmap
+		 * reclaimable.  But for now, simply allocating the whole bitmap
+		 * is a simple solution that works well on the files on which
+		 * fsverity is realistically used.  E.g., with SHA-256 and 4K
+		 * blocks, a 100MB file only needs a 24-byte bitmap, and the
+		 * bitmap for any file under 17GB fits in a 4K page.
+		 */
+		unsigned long num_bits =
+			vi->tree_params.tree_pages <<
+			vi->tree_params.log_blocks_per_page;
+
+		vi->hash_block_verified = kvcalloc(BITS_TO_LONGS(num_bits),
+						   sizeof(unsigned long),
+						   GFP_KERNEL);
+		if (!vi->hash_block_verified) {
+			err = -ENOMEM;
+			goto fail;
+		}
+		spin_lock_init(&vi->hash_page_init_lock);
+	}
+
+	return vi;
+
+fail:
+	fsverity_free_info(vi);
+	return ERR_PTR(err);
+}
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
+{
+	/*
+	 * Multiple tasks may race to set ->i_verity_info, so use
+	 * cmpxchg_release().  This pairs with the smp_load_acquire() in
+	 * fsverity_get_info().  I.e., here we publish ->i_verity_info with a
+	 * RELEASE barrier so that other tasks can ACQUIRE it.
+	 */
+	if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
+		/* Lost the race, so free the fsverity_info we allocated. */
+		fsverity_free_info(vi);
+		/*
+		 * Afterwards, the caller may access ->i_verity_info directly,
+		 * so make sure to ACQUIRE the winning fsverity_info.
+		 */
+		(void)fsverity_get_info(inode);
+	}
+}
+
+void fsverity_free_info(struct fsverity_info *vi)
+{
+	if (!vi)
+		return;
+	kfree(vi->tree_params.hashstate);
+	kvfree(vi->hash_block_verified);
+	kmem_cache_free(fsverity_info_cachep, vi);
+}
+
+static bool validate_fsverity_descriptor(struct inode *inode,
+					 const struct fsverity_descriptor *desc,
+					 size_t desc_size)
+{
+	if (desc_size < sizeof(*desc)) {
+		fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
+			     desc_size);
+		return false;
+	}
+
+	if (desc->version != 1) {
+		fsverity_err(inode, "Unrecognized descriptor version: %u",
+			     desc->version);
+		return false;
+	}
+
+	if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
+		fsverity_err(inode, "Reserved bits set in descriptor");
+		return false;
+	}
+
+	if (desc->salt_size > sizeof(desc->salt)) {
+		fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
+		return false;
+	}
+
+	if (le64_to_cpu(desc->data_size) != inode->i_size) {
+		fsverity_err(inode,
+			     "Wrong data_size: %llu (desc) != %lld (inode)",
+			     le64_to_cpu(desc->data_size), inode->i_size);
+		return false;
+	}
+
+	if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
+		fsverity_err(inode, "Signature overflows verity descriptor");
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Read the inode's fsverity_descriptor (with optional appended builtin
+ * signature) from the filesystem, and do basic validation of it.
+ */
+int fsverity_get_descriptor(struct inode *inode,
+			    struct fsverity_descriptor **desc_ret)
+{
+	int res;
+	struct fsverity_descriptor *desc;
+
+	res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
+	if (res < 0) {
+		fsverity_err(inode,
+			     "Error %d getting verity descriptor size", res);
+		return res;
+	}
+	if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
+		fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
+			     res);
+		return -EMSGSIZE;
+	}
+	desc = kmalloc(res, GFP_KERNEL);
+	if (!desc)
+		return -ENOMEM;
+	res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
+	if (res < 0) {
+		fsverity_err(inode, "Error %d reading verity descriptor", res);
+		kfree(desc);
+		return res;
+	}
+
+	if (!validate_fsverity_descriptor(inode, desc, res)) {
+		kfree(desc);
+		return -EINVAL;
+	}
+
+	*desc_ret = desc;
+	return 0;
+}
+
+/* Ensure the inode has an ->i_verity_info */
+static int ensure_verity_info(struct inode *inode)
+{
+	struct fsverity_info *vi = fsverity_get_info(inode);
+	struct fsverity_descriptor *desc;
+	int err;
+
+	if (vi)
+		return 0;
+
+	err = fsverity_get_descriptor(inode, &desc);
+	if (err)
+		return err;
+
+	vi = fsverity_create_info(inode, desc);
+	if (IS_ERR(vi)) {
+		err = PTR_ERR(vi);
+		goto out_free_desc;
+	}
+
+	fsverity_set_info(inode, vi);
+	err = 0;
+out_free_desc:
+	kfree(desc);
+	return err;
+}
+
+int __fsverity_file_open(struct inode *inode, struct file *filp)
+{
+	if (filp->f_mode & FMODE_WRITE)
+		return -EPERM;
+	return ensure_verity_info(inode);
+}
+EXPORT_SYMBOL_GPL(__fsverity_file_open);
+
+int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	if (attr->ia_valid & ATTR_SIZE)
+		return -EPERM;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__fsverity_prepare_setattr);
+
+void __fsverity_cleanup_inode(struct inode *inode)
+{
+	fsverity_free_info(inode->i_verity_info);
+	inode->i_verity_info = NULL;
+}
+EXPORT_SYMBOL_GPL(__fsverity_cleanup_inode);
+
+void __init fsverity_init_info_cache(void)
+{
+	fsverity_info_cachep = KMEM_CACHE_USERCOPY(
+					fsverity_info,
+					SLAB_RECLAIM_ACCOUNT | SLAB_PANIC,
+					file_digest);
+}