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 return u_sock;
38 }
39 EXPORT_SYMBOL(unix_get_socket);
40
41 /* Keep the number of times in flight count for the file
42 * descriptor if it is for an AF_UNIX socket.
43 */
unix_inflight(struct user_struct * user,struct file * fp)44 void unix_inflight(struct user_struct *user, struct file *fp)
45 {
46 struct sock *s = unix_get_socket(fp);
47
48 spin_lock(&unix_gc_lock);
49
50 if (s) {
51 struct unix_sock *u = unix_sk(s);
52
53 if (atomic_long_inc_return(&u->inflight) == 1) {
54 BUG_ON(!list_empty(&u->link));
55 list_add_tail(&u->link, &gc_inflight_list);
56 } else {
57 BUG_ON(list_empty(&u->link));
58 }
59 /* Paired with READ_ONCE() in wait_for_unix_gc() */
60 WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + 1);
61 }
62 user->unix_inflight++;
63 spin_unlock(&unix_gc_lock);
64 }
65
unix_notinflight(struct user_struct * user,struct file * fp)66 void unix_notinflight(struct user_struct *user, struct file *fp)
67 {
68 struct sock *s = unix_get_socket(fp);
69
70 spin_lock(&unix_gc_lock);
71
72 if (s) {
73 struct unix_sock *u = unix_sk(s);
74
75 BUG_ON(!atomic_long_read(&u->inflight));
76 BUG_ON(list_empty(&u->link));
77
78 if (atomic_long_dec_and_test(&u->inflight))
79 list_del_init(&u->link);
80 /* Paired with READ_ONCE() in wait_for_unix_gc() */
81 WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - 1);
82 }
83 user->unix_inflight--;
84 spin_unlock(&unix_gc_lock);
85 }
86
87 /*
88 * The "user->unix_inflight" variable is protected by the garbage
89 * collection lock, and we just read it locklessly here. If you go
90 * over the limit, there might be a tiny race in actually noticing
91 * it across threads. Tough.
92 */
too_many_unix_fds(struct task_struct * p)93 static inline bool too_many_unix_fds(struct task_struct *p)
94 {
95 struct user_struct *user = current_user();
96
97 if (unlikely(user->unix_inflight > task_rlimit(p, RLIMIT_NOFILE)))
98 return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
99 return false;
100 }
101
102 #define MAX_RECURSION_LEVEL 4
103
unix_attach_fds(struct scm_cookie * scm,struct sk_buff * skb)104 int unix_attach_fds(struct scm_cookie *scm, struct sk_buff *skb)
105 {
106 int i;
107 unsigned char max_level = 0;
108
109 if (too_many_unix_fds(current))
110 return -ETOOMANYREFS;
111
112 for (i = scm->fp->count - 1; i >= 0; i--) {
113 struct sock *sk = unix_get_socket(scm->fp->fp[i]);
114
115 if (sk)
116 max_level = max(max_level,
117 unix_sk(sk)->recursion_level);
118 }
119 if (unlikely(max_level > MAX_RECURSION_LEVEL))
120 return -ETOOMANYREFS;
121
122 /*
123 * Need to duplicate file references for the sake of garbage
124 * collection. Otherwise a socket in the fps might become a
125 * candidate for GC while the skb is not yet queued.
126 */
127 UNIXCB(skb).fp = scm_fp_dup(scm->fp);
128 if (!UNIXCB(skb).fp)
129 return -ENOMEM;
130
131 for (i = scm->fp->count - 1; i >= 0; i--)
132 unix_inflight(scm->fp->user, scm->fp->fp[i]);
133 return max_level;
134 }
135 EXPORT_SYMBOL(unix_attach_fds);
136
unix_detach_fds(struct scm_cookie * scm,struct sk_buff * skb)137 void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
138 {
139 int i;
140
141 scm->fp = UNIXCB(skb).fp;
142 UNIXCB(skb).fp = NULL;
143
144 for (i = scm->fp->count-1; i >= 0; i--)
145 unix_notinflight(scm->fp->user, scm->fp->fp[i]);
146 }
147 EXPORT_SYMBOL(unix_detach_fds);
148
unix_destruct_scm(struct sk_buff * skb)149 void unix_destruct_scm(struct sk_buff *skb)
150 {
151 struct scm_cookie scm;
152
153 memset(&scm, 0, sizeof(scm));
154 scm.pid = UNIXCB(skb).pid;
155 if (UNIXCB(skb).fp)
156 unix_detach_fds(&scm, skb);
157
158 /* Alas, it calls VFS */
159 /* So fscking what? fput() had been SMP-safe since the last Summer */
160 scm_destroy(&scm);
161 sock_wfree(skb);
162 }
163 EXPORT_SYMBOL(unix_destruct_scm);
164