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		const struct proto_ops *ops = READ_ONCE(sock->ops);
 33		struct sock *s = sock->sk;
 34
 35		/* PF_UNIX ? */
 36		if (s && ops && ops->family == PF_UNIX)
 37			u_sock = s;
 38	}
 39
 40	return u_sock;
 41}
 42EXPORT_SYMBOL(unix_get_socket);
 43
 44/* Keep the number of times in flight count for the file
 45 * descriptor if it is for an AF_UNIX socket.
 46 */
 47void unix_inflight(struct user_struct *user, struct file *fp)
 48{
 49	struct sock *s = unix_get_socket(fp);
 50
 51	spin_lock(&unix_gc_lock);
 52
 53	if (s) {
 54		struct unix_sock *u = unix_sk(s);
 55
 56		if (atomic_long_inc_return(&u->inflight) == 1) {
 57			BUG_ON(!list_empty(&u->link));
 58			list_add_tail(&u->link, &gc_inflight_list);
 59		} else {
 60			BUG_ON(list_empty(&u->link));
 61		}
 62		/* Paired with READ_ONCE() in wait_for_unix_gc() */
 63		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + 1);
 64	}
 65	WRITE_ONCE(user->unix_inflight, user->unix_inflight + 1);
 66	spin_unlock(&unix_gc_lock);
 67}
 68
 69void unix_notinflight(struct user_struct *user, struct file *fp)
 70{
 71	struct sock *s = unix_get_socket(fp);
 72
 73	spin_lock(&unix_gc_lock);
 74
 75	if (s) {
 76		struct unix_sock *u = unix_sk(s);
 77
 78		BUG_ON(!atomic_long_read(&u->inflight));
 79		BUG_ON(list_empty(&u->link));
 80
 81		if (atomic_long_dec_and_test(&u->inflight))
 82			list_del_init(&u->link);
 83		/* Paired with READ_ONCE() in wait_for_unix_gc() */
 84		WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - 1);
 85	}
 86	WRITE_ONCE(user->unix_inflight, user->unix_inflight - 1);
 87	spin_unlock(&unix_gc_lock);
 88}
 89
 90/*
 91 * The "user->unix_inflight" variable is protected by the garbage
 92 * collection lock, and we just read it locklessly here. If you go
 93 * over the limit, there might be a tiny race in actually noticing
 94 * it across threads. Tough.
 95 */
 96static inline bool too_many_unix_fds(struct task_struct *p)
 97{
 98	struct user_struct *user = current_user();
 99
100	if (unlikely(READ_ONCE(user->unix_inflight) > task_rlimit(p, RLIMIT_NOFILE)))
101		return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
102	return false;
103}
104
105int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
106{
107	int i;
108
109	if (too_many_unix_fds(current))
110		return -ETOOMANYREFS;
111
112	/*
113	 * Need to duplicate file references for the sake of garbage
114	 * collection.  Otherwise a socket in the fps might become a
115	 * candidate for GC while the skb is not yet queued.
116	 */
117	UNIXCB(skb).fp = scm_fp_dup(scm->fp);
118	if (!UNIXCB(skb).fp)
119		return -ENOMEM;
120
121	for (i = scm->fp->count - 1; i >= 0; i--)
122		unix_inflight(scm->fp->user, scm->fp->fp[i]);
123	return 0;
124}
125EXPORT_SYMBOL(unix_attach_fds);
126
127void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
128{
129	int i;
130
131	scm->fp = UNIXCB(skb).fp;
132	UNIXCB(skb).fp = NULL;
133
134	for (i = scm->fp->count-1; i >= 0; i--)
135		unix_notinflight(scm->fp->user, scm->fp->fp[i]);
136}
137EXPORT_SYMBOL(unix_detach_fds);
138
139void unix_destruct_scm(struct sk_buff *skb)
140{
141	struct scm_cookie scm;
142
143	memset(&scm, 0, sizeof(scm));
144	scm.pid  = UNIXCB(skb).pid;
145	if (UNIXCB(skb).fp)
146		unix_detach_fds(&scm, skb);
147
148	/* Alas, it calls VFS */
149	/* So fscking what? fput() had been SMP-safe since the last Summer */
150	scm_destroy(&scm);
151	sock_wfree(skb);
152}
153EXPORT_SYMBOL(unix_destruct_scm);
154
155void io_uring_destruct_scm(struct sk_buff *skb)
156{
157	unix_destruct_scm(skb);
158}
159EXPORT_SYMBOL(io_uring_destruct_scm);