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// 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"
static int pidfd_release(struct inode *inode, struct file *file)
{
#ifndef CONFIG_FS_PID
struct pid *pid = file->private_data;
file->private_data = NULL;
put_pid(pid);
#endif
return 0;
}
#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 = {
.release = pidfd_release,
.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);
#ifdef CONFIG_FS_PID
return file_inode(file)->i_private;
#else
return file->private_data;
#endif
}
#ifdef CONFIG_FS_PID
static struct vfsmount *pidfs_mnt __ro_after_init;
/*
* 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);
}
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)
{
return dynamic_dname(buffer, buflen, "pidfd:[%lu]",
d_inode(dentry)->i_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_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;
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;
/*
* Inode numbering for pidfs start at RESERVED_PIDS + 1.
* This avoids collisions with the root inode which is 1
* for pseudo filesystems.
*/
ret = path_from_stashed(&pid->stashed, pid->ino, pidfs_mnt,
&pidfs_file_operations, &pidfs_inode_operations,
get_pid(pid), &path);
if (ret <= 0)
put_pid(pid);
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");
}
bool is_pidfs_sb(const struct super_block *sb)
{
return sb == pidfs_mnt->mnt_sb;
}
#else /* !CONFIG_FS_PID */
struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
{
struct file *pidfd_file;
pidfd_file = anon_inode_getfile("[pidfd]", &pidfs_file_operations, pid,
flags | O_RDWR);
if (IS_ERR(pidfd_file))
return pidfd_file;
get_pid(pid);
return pidfd_file;
}
void __init pidfs_init(void) { }
bool is_pidfs_sb(const struct super_block *sb)
{
return false;
}
#endif
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