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-rw-r--r--fs/pidfs.c283
1 files changed, 283 insertions, 0 deletions
diff --git a/fs/pidfs.c b/fs/pidfs.c
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index 0000000000..a63d5d24aa
--- /dev/null
+++ b/fs/pidfs.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/anon_inodes.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/magic.h>
+#include <linux/mount.h>
+#include <linux/pid.h>
+#include <linux/pidfs.h>
+#include <linux/pid_namespace.h>
+#include <linux/poll.h>
+#include <linux/proc_fs.h>
+#include <linux/proc_ns.h>
+#include <linux/pseudo_fs.h>
+#include <linux/seq_file.h>
+#include <uapi/linux/pidfd.h>
+
+#include "internal.h"
+
+#ifdef CONFIG_PROC_FS
+/**
+ * pidfd_show_fdinfo - print information about a pidfd
+ * @m: proc fdinfo file
+ * @f: file referencing a pidfd
+ *
+ * Pid:
+ * This function will print the pid that a given pidfd refers to in the
+ * pid namespace of the procfs instance.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its pid. This is
+ * similar to calling getppid() on a process whose parent is outside of
+ * its pid namespace.
+ *
+ * NSpid:
+ * If pid namespaces are supported then this function will also print
+ * the pid of a given pidfd refers to for all descendant pid namespaces
+ * starting from the current pid namespace of the instance, i.e. the
+ * Pid field and the first entry in the NSpid field will be identical.
+ * If the pid namespace of the process is not a descendant of the pid
+ * namespace of the procfs instance 0 will be shown as its first NSpid
+ * entry and no others will be shown.
+ * Note that this differs from the Pid and NSpid fields in
+ * /proc/<pid>/status where Pid and NSpid are always shown relative to
+ * the pid namespace of the procfs instance. The difference becomes
+ * obvious when sending around a pidfd between pid namespaces from a
+ * different branch of the tree, i.e. where no ancestral relation is
+ * present between the pid namespaces:
+ * - create two new pid namespaces ns1 and ns2 in the initial pid
+ * namespace (also take care to create new mount namespaces in the
+ * new pid namespace and mount procfs)
+ * - create a process with a pidfd in ns1
+ * - send pidfd from ns1 to ns2
+ * - read /proc/self/fdinfo/<pidfd> and observe that both Pid and NSpid
+ * have exactly one entry, which is 0
+ */
+static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct pid *pid = pidfd_pid(f);
+ struct pid_namespace *ns;
+ pid_t nr = -1;
+
+ if (likely(pid_has_task(pid, PIDTYPE_PID))) {
+ ns = proc_pid_ns(file_inode(m->file)->i_sb);
+ nr = pid_nr_ns(pid, ns);
+ }
+
+ seq_put_decimal_ll(m, "Pid:\t", nr);
+
+#ifdef CONFIG_PID_NS
+ seq_put_decimal_ll(m, "\nNSpid:\t", nr);
+ if (nr > 0) {
+ int i;
+
+ /* If nr is non-zero it means that 'pid' is valid and that
+ * ns, i.e. the pid namespace associated with the procfs
+ * instance, is in the pid namespace hierarchy of pid.
+ * Start at one below the already printed level.
+ */
+ for (i = ns->level + 1; i <= pid->level; i++)
+ seq_put_decimal_ll(m, "\t", pid->numbers[i].nr);
+ }
+#endif
+ seq_putc(m, '\n');
+}
+#endif
+
+/*
+ * Poll support for process exit notification.
+ */
+static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts)
+{
+ struct pid *pid = pidfd_pid(file);
+ bool thread = file->f_flags & PIDFD_THREAD;
+ struct task_struct *task;
+ __poll_t poll_flags = 0;
+
+ poll_wait(file, &pid->wait_pidfd, pts);
+ /*
+ * Depending on PIDFD_THREAD, inform pollers when the thread
+ * or the whole thread-group exits.
+ */
+ guard(rcu)();
+ task = pid_task(pid, PIDTYPE_PID);
+ if (!task)
+ poll_flags = EPOLLIN | EPOLLRDNORM | EPOLLHUP;
+ else if (task->exit_state && (thread || thread_group_empty(task)))
+ poll_flags = EPOLLIN | EPOLLRDNORM;
+
+ return poll_flags;
+}
+
+static const struct file_operations pidfs_file_operations = {
+ .poll = pidfd_poll,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = pidfd_show_fdinfo,
+#endif
+};
+
+struct pid *pidfd_pid(const struct file *file)
+{
+ if (file->f_op != &pidfs_file_operations)
+ return ERR_PTR(-EBADF);
+ return file_inode(file)->i_private;
+}
+
+static struct vfsmount *pidfs_mnt __ro_after_init;
+
+#if BITS_PER_LONG == 32
+/*
+ * Provide a fallback mechanism for 32-bit systems so processes remain
+ * reliably comparable by inode number even on those systems.
+ */
+static DEFINE_IDA(pidfd_inum_ida);
+
+static int pidfs_inum(struct pid *pid, unsigned long *ino)
+{
+ int ret;
+
+ ret = ida_alloc_range(&pidfd_inum_ida, RESERVED_PIDS + 1,
+ UINT_MAX, GFP_ATOMIC);
+ if (ret < 0)
+ return -ENOSPC;
+
+ *ino = ret;
+ return 0;
+}
+
+static inline void pidfs_free_inum(unsigned long ino)
+{
+ if (ino > 0)
+ ida_free(&pidfd_inum_ida, ino);
+}
+#else
+static inline int pidfs_inum(struct pid *pid, unsigned long *ino)
+{
+ *ino = pid->ino;
+ return 0;
+}
+#define pidfs_free_inum(ino) ((void)(ino))
+#endif
+
+/*
+ * The vfs falls back to simple_setattr() if i_op->setattr() isn't
+ * implemented. Let's reject it completely until we have a clean
+ * permission concept for pidfds.
+ */
+static int pidfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+ struct iattr *attr)
+{
+ return -EOPNOTSUPP;
+}
+
+static int pidfs_getattr(struct mnt_idmap *idmap, const struct path *path,
+ struct kstat *stat, u32 request_mask,
+ unsigned int query_flags)
+{
+ struct inode *inode = d_inode(path->dentry);
+
+ generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
+ return 0;
+}
+
+static const struct inode_operations pidfs_inode_operations = {
+ .getattr = pidfs_getattr,
+ .setattr = pidfs_setattr,
+};
+
+static void pidfs_evict_inode(struct inode *inode)
+{
+ struct pid *pid = inode->i_private;
+
+ clear_inode(inode);
+ put_pid(pid);
+ pidfs_free_inum(inode->i_ino);
+}
+
+static const struct super_operations pidfs_sops = {
+ .drop_inode = generic_delete_inode,
+ .evict_inode = pidfs_evict_inode,
+ .statfs = simple_statfs,
+};
+
+static char *pidfs_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+ struct inode *inode = d_inode(dentry);
+ struct pid *pid = inode->i_private;
+
+ return dynamic_dname(buffer, buflen, "pidfd:[%llu]", pid->ino);
+}
+
+static const struct dentry_operations pidfs_dentry_operations = {
+ .d_delete = always_delete_dentry,
+ .d_dname = pidfs_dname,
+ .d_prune = stashed_dentry_prune,
+};
+
+static int pidfs_init_inode(struct inode *inode, void *data)
+{
+ inode->i_private = data;
+ inode->i_flags |= S_PRIVATE;
+ inode->i_mode |= S_IRWXU;
+ inode->i_op = &pidfs_inode_operations;
+ inode->i_fop = &pidfs_file_operations;
+ /*
+ * Inode numbering for pidfs start at RESERVED_PIDS + 1. This
+ * avoids collisions with the root inode which is 1 for pseudo
+ * filesystems.
+ */
+ return pidfs_inum(data, &inode->i_ino);
+}
+
+static void pidfs_put_data(void *data)
+{
+ struct pid *pid = data;
+ put_pid(pid);
+}
+
+static const struct stashed_operations pidfs_stashed_ops = {
+ .init_inode = pidfs_init_inode,
+ .put_data = pidfs_put_data,
+};
+
+static int pidfs_init_fs_context(struct fs_context *fc)
+{
+ struct pseudo_fs_context *ctx;
+
+ ctx = init_pseudo(fc, PID_FS_MAGIC);
+ if (!ctx)
+ return -ENOMEM;
+
+ ctx->ops = &pidfs_sops;
+ ctx->dops = &pidfs_dentry_operations;
+ fc->s_fs_info = (void *)&pidfs_stashed_ops;
+ return 0;
+}
+
+static struct file_system_type pidfs_type = {
+ .name = "pidfs",
+ .init_fs_context = pidfs_init_fs_context,
+ .kill_sb = kill_anon_super,
+};
+
+struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
+{
+
+ struct file *pidfd_file;
+ struct path path;
+ int ret;
+
+ ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
+ if (ret < 0)
+ return ERR_PTR(ret);
+
+ pidfd_file = dentry_open(&path, flags, current_cred());
+ path_put(&path);
+ return pidfd_file;
+}
+
+void __init pidfs_init(void)
+{
+ pidfs_mnt = kern_mount(&pidfs_type);
+ if (IS_ERR(pidfs_mnt))
+ panic("Failed to mount pidfs pseudo filesystem");
+}