path: root/fs/pidfs.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/anon_inodes.h>
#include <linux/exportfs.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/cgroup.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/ptrace.h>
#include <linux/seq_file.h>
#include <uapi/linux/pidfd.h>
#include <linux/ipc_namespace.h>
#include <linux/time_namespace.h>
#include <linux/utsname.h>
#include <net/net_namespace.h>
#include <linux/coredump.h>
#include <linux/xattr.h>

#include "internal.h"
#include "mount.h"

#define PIDFS_PID_DEAD ERR_PTR(-ESRCH)

static struct kmem_cache *pidfs_attr_cachep __ro_after_init;
static struct kmem_cache *pidfs_xattr_cachep __ro_after_init;

static struct path pidfs_root_path = {};

void pidfs_get_root(struct path *path)
{
	*path = pidfs_root_path;
	path_get(path);
}

enum pidfs_attr_mask_bits {
	PIDFS_ATTR_BIT_EXIT	= 0,
	PIDFS_ATTR_BIT_COREDUMP	= 1,
};

struct pidfs_attr {
	unsigned long attr_mask;
	struct simple_xattrs *xattrs;
	struct /* exit info */ {
		__u64 cgroupid;
		__s32 exit_code;
	};
	__u32 coredump_mask;
	__u32 coredump_signal;
};

static struct rb_root pidfs_ino_tree = RB_ROOT;

#if BITS_PER_LONG == 32
static inline unsigned long pidfs_ino(u64 ino)
{
	return lower_32_bits(ino);
}

/* On 32 bit the generation number are the upper 32 bits. */
static inline u32 pidfs_gen(u64 ino)
{
	return upper_32_bits(ino);
}

#else

/* On 64 bit simply return ino. */
static inline unsigned long pidfs_ino(u64 ino)
{
	return ino;
}

/* On 64 bit the generation number is 0. */
static inline u32 pidfs_gen(u64 ino)
{
	return 0;
}
#endif

static int pidfs_ino_cmp(struct rb_node *a, const struct rb_node *b)
{
	struct pid *pid_a = rb_entry(a, struct pid, pidfs_node);
	struct pid *pid_b = rb_entry(b, struct pid, pidfs_node);
	u64 pid_ino_a = pid_a->ino;
	u64 pid_ino_b = pid_b->ino;

	if (pid_ino_a < pid_ino_b)
		return -1;
	if (pid_ino_a > pid_ino_b)
		return 1;
	return 0;
}

void pidfs_add_pid(struct pid *pid)
{
	static u64 pidfs_ino_nr = 2;

	/*
	 * On 64 bit nothing special happens. The 64bit number assigned
	 * to struct pid is the inode number.
	 *
	 * On 32 bit the 64 bit number assigned to struct pid is split
	 * into two 32 bit numbers. The lower 32 bits are used as the
	 * inode number and the upper 32 bits are used as the inode
	 * generation number.
	 *
	 * On 32 bit pidfs_ino() will return the lower 32 bit. When
	 * pidfs_ino() returns zero a wrap around happened. When a
	 * wraparound happens the 64 bit number will be incremented by 2
	 * so inode numbering starts at 2 again.
	 *
	 * On 64 bit comparing two pidfds is as simple as comparing
	 * inode numbers.
	 *
	 * When a wraparound happens on 32 bit multiple pidfds with the
	 * same inode number are likely to exist (This isn't a problem
	 * since before pidfs pidfds used the anonymous inode meaning
	 * all pidfds had the same inode number.). Userspace can
	 * reconstruct the 64 bit identifier by retrieving both the
	 * inode number and the inode generation number to compare or
	 * use file handles.
	 */
	if (pidfs_ino(pidfs_ino_nr) == 0)
		pidfs_ino_nr += 2;

	pid->ino = pidfs_ino_nr;
	pid->stashed = NULL;
	pid->attr = NULL;
	pidfs_ino_nr++;

	write_seqcount_begin(&pidmap_lock_seq);
	rb_find_add_rcu(&pid->pidfs_node, &pidfs_ino_tree, pidfs_ino_cmp);
	write_seqcount_end(&pidmap_lock_seq);
}

void pidfs_remove_pid(struct pid *pid)
{
	write_seqcount_begin(&pidmap_lock_seq);
	rb_erase(&pid->pidfs_node, &