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