1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/module.h>
  3#include <linux/kernel.h>
  4#include <linux/string.h>
  5#include <linux/socket.h>
  6#include <linux/net.h>
  7#include <linux/fs.h>
  8#include <net/af_unix.h>
  9#include <net/scm.h>
 10#include <linux/init.h>
 11#include <linux/io_uring.h>
 12
 13#include "scm.h"
 14
 15unsigned int unix_tot_inflight;
 16EXPORT_SYMBOL(unix_tot_inflight);
 17
 18LIST_HEAD(gc_inflight_list);
 19EXPORT_SYMBOL(gc_inflight_list);
 20
 21DEFINE_SPINLOCK(unix_gc_lock);
 22EXPORT_SYMBOL(unix_gc_lock);
 23
 24struct sock *unix_get_socket(struct file *filp)
 25{
 26	struct sock *u_sock = NULL;
 27	struct inode *inode = file_inode(filp);
 28
 29	/* Socket ? */
 30	if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
 31		struct socket *sock = SOCKET_I(inode);
 32		struct sock *s = sock->sk;
 33
 34		/* PF_UNIX ? */
 35		if (s && sock->ops && sock->ops->family == PF_UNIX)
 36			u_sock = s;
 37	} else {
 38		/* Could be an io_uring instance */
 39		u_sock = io_uring_get_socket(filp);
 40	}
 41	return u_sock;
 42}
 43EXPORT_SYMBOL(unix_get_socket);
 44
 45/* Keep the number of times in flight count for the file
 46 * descriptor if it is for an AF_UNIX socket.
 47 */
 48void unix_inflight(struct user_struct *user, struct file *fp)
 49{
 50	struct sock *s = unix_get_socket(fp);
 51
 52	spin_lock(&unix_gc_lock);
 53
 54	if (s) {
 55		struct unix_sock *u = unix_sk(s);
 56
 57		if (atomic_long_inc_return(&u->inflight) == 1) {
 58			BUG_ON(!list_empty(&u->link));
 59			list_add_tail(&u->link, &gc_inflight_list);
 60		} else {
 61			BUG_ON(list_empty(&u->link));
 62		}
 63		/* Paired with READ_ONCE() in wait_for_unix_gc() */
 64		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + 1);
 65	}
 66	user->unix_inflight++;
 67	spin_unlock(&unix_gc_lock);
 68}
 69
 70void unix_notinflight(struct user_struct *user, struct file *fp)
 71{
 72	struct sock *s = unix_get_socket(fp);
 73
 74	spin_lock(&unix_gc_lock);
 75
 76	if (s) {
 77		struct unix_sock *u = unix_sk(s);
 78
 79		BUG_ON(!atomic_long_read(&u->inflight));
 80		BUG_ON(list_empty(&u->link));
 81
 82		if (atomic_long_dec_and_test(&u->inflight))
 83			list_del_init(&u->link);
 84		/* Paired with READ_ONCE() in wait_for_unix_gc() */
 85		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - 1);
 86	}
 87	user->unix_inflight--;
 88	spin_unlock(&unix_gc_lock);
 89}
 90
 91/*
 92 * The "user->unix_inflight" variable is protected by the garbage
 93 * collection lock, and we just read it locklessly here. If you go
 94 * over the limit, there might be a tiny race in actually noticing
 95 * it across threads. Tough.
 96 */
 97static inline bool too_many_unix_fds(struct task_struct *p)
 98{
 99	struct user_struct *user = current_user();
100
101	if (unlikely(user->unix_inflight > task_rlimit(p, RLIMIT_NOFILE)))
102		return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
103	return false;
104}
105
106int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
107{
108	int i;
109
110	if (too_many_unix_fds(current))
111		return -ETOOMANYREFS;
112
113	/*
114	 * Need to duplicate file references for the sake of garbage
115	 * collection.  Otherwise a socket in the fps might become a
116	 * candidate for GC while the skb is not yet queued.
117	 */
118	UNIXCB(skb).fp = scm_fp_dup(scm->fp);
119	if (!UNIXCB(skb).fp)
120		return -ENOMEM;
121
122	for (i = scm->fp->count - 1; i >= 0; i--)
123		unix_inflight(scm->fp->user, scm->fp->fp[i]);
124	return 0;
125}
126EXPORT_SYMBOL(unix_attach_fds);
127
128void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
129{
130	int i;
131
132	scm->fp = UNIXCB(skb).fp;
133	UNIXCB(skb).fp = NULL;
134
135	for (i = scm->fp->count-1; i >= 0; i--)
136		unix_notinflight(scm->fp->user, scm->fp->fp[i]);
137}
138EXPORT_SYMBOL(unix_detach_fds);
139
140void unix_destruct_scm(struct sk_buff *skb)
141{
142	struct scm_cookie scm;
143
144	memset(&scm, 0, sizeof(scm));
145	scm.pid  = UNIXCB(skb).pid;
146	if (UNIXCB(skb).fp)
147		unix_detach_fds(&scm, skb);
148
149	/* Alas, it calls VFS */
150	/* So fscking what? fput() had been SMP-safe since the last Summer */
151	scm_destroy(&scm);
152	sock_wfree(skb);
153}
154EXPORT_SYMBOL(unix_destruct_scm);