1 /*
2 * NET3: Garbage Collector For AF_UNIX sockets
3 *
4 * Garbage Collector:
5 * Copyright (C) Barak A. Pearlmutter.
6 * Released under the GPL version 2 or later.
7 *
8 * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem.
9 * If it doesn't work blame me, it worked when Barak sent it.
10 *
11 * Assumptions:
12 *
13 * - object w/ a bit
14 * - free list
15 *
16 * Current optimizations:
17 *
18 * - explicit stack instead of recursion
19 * - tail recurse on first born instead of immediate push/pop
20 * - we gather the stuff that should not be killed into tree
21 * and stack is just a path from root to the current pointer.
22 *
23 * Future optimizations:
24 *
25 * - don't just push entire root set; process in place
26 *
27 * This program is free software; you can redistribute it and/or
28 * modify it under the terms of the GNU General Public License
29 * as published by the Free Software Foundation; either version
30 * 2 of the License, or (at your option) any later version.
31 *
32 * Fixes:
33 * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
34 * Cope with changing max_files.
35 * Al Viro 11 Oct 1998
36 * Graph may have cycles. That is, we can send the descriptor
37 * of foo to bar and vice versa. Current code chokes on that.
38 * Fix: move SCM_RIGHTS ones into the separate list and then
39 * skb_free() them all instead of doing explicit fput's.
40 * Another problem: since fput() may block somebody may
41 * create a new unix_socket when we are in the middle of sweep
42 * phase. Fix: revert the logic wrt MARKED. Mark everything
43 * upon the beginning and unmark non-junk ones.
44 *
45 * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
46 * sent to connect()'ed but still not accept()'ed sockets.
47 * Fixed. Old code had slightly different problem here:
48 * extra fput() in situation when we passed the descriptor via
49 * such socket and closed it (descriptor). That would happen on
50 * each unix_gc() until the accept(). Since the struct file in
51 * question would go to the free list and might be reused...
52 * That might be the reason of random oopses on filp_close()
53 * in unrelated processes.
54 *
55 * AV 28 Feb 1999
56 * Kill the explicit allocation of stack. Now we keep the tree
57 * with root in dummy + pointer (gc_current) to one of the nodes.
58 * Stack is represented as path from gc_current to dummy. Unmark
59 * now means "add to tree". Push == "make it a son of gc_current".
60 * Pop == "move gc_current to parent". We keep only pointers to
61 * parents (->gc_tree).
62 * AV 1 Mar 1999
63 * Damn. Added missing check for ->dead in listen queues scanning.
64 *
65 */
66
67 #include <linux/kernel.h>
68 #include <linux/sched.h>
69 #include <linux/string.h>
70 #include <linux/socket.h>
71 #include <linux/un.h>
72 #include <linux/net.h>
73 #include <linux/fs.h>
74 #include <linux/malloc.h>
75 #include <linux/skbuff.h>
76 #include <linux/netdevice.h>
77 #include <linux/file.h>
78 #include <linux/proc_fs.h>
79
80 #include <net/sock.h>
81 #include <net/tcp.h>
82 #include <net/af_unix.h>
83 #include <net/scm.h>
84
85 /* Internal data structures and random procedures: */
86
87 #define GC_HEAD ((unix_socket *)(-1))
88 #define GC_ORPHAN ((unix_socket *)(-3))
89
90 static unix_socket *gc_current=GC_HEAD; /* stack of objects to mark */
91
92 atomic_t unix_tot_inflight = ATOMIC_INIT(0);
93
94
95 extern inline unix_socket *unix_get_socket(struct file *filp)
96 {
97 unix_socket * u_sock = NULL;
98 struct inode *inode = filp->f_dentry->d_inode;
99
100 /*
101 * Socket ?
102 */
103 if (inode->i_sock) {
104 struct socket * sock = &inode->u.socket_i;
105 struct sock * s = sock->sk;
106
107 /*
108 * PF_UNIX ?
109 */
110 if (s && sock->ops && sock->ops->family == PF_UNIX)
111 u_sock = s;
112 }
113 return u_sock;
114 }
115
116 /*
117 * Keep the number of times in flight count for the file
118 * descriptor if it is for an AF_UNIX socket.
119 */
120
121 void unix_inflight(struct file *fp)
122 {
123 unix_socket *s=unix_get_socket(fp);
124 if(s) {
125 atomic_inc(&s->protinfo.af_unix.inflight);
126 atomic_inc(&unix_tot_inflight);
127 }
128 }
129
130 void unix_notinflight(struct file *fp)
131 {
132 unix_socket *s=unix_get_socket(fp);
133 if(s) {
134 atomic_dec(&s->protinfo.af_unix.inflight);
135 atomic_dec(&unix_tot_inflight);
136 }
137 }
138
139
140 /*
141 * Garbage Collector Support Functions
142 */
143
144 extern inline unix_socket *pop_stack(void)
145 {
146 unix_socket *p=gc_current;
147 gc_current = p->protinfo.af_unix.gc_tree;
148 return p;
149 }
150
151 extern inline int empty_stack(void)
152 {
153 return gc_current == GC_HEAD;
154 }
155
156 extern inline void maybe_unmark_and_push(unix_socket *x)
157 {
158 if (x->protinfo.af_unix.gc_tree != GC_ORPHAN)
159 return;
160 sock_hold(x);
161 x->protinfo.af_unix.gc_tree = gc_current;
162 gc_current = x;
163 }
164
165
166 /* The external entry point: unix_gc() */
167
168 void unix_gc(void)
169 {
170 static DECLARE_MUTEX(unix_gc_sem);
171 int i;
172 unix_socket *s;
173 struct sk_buff_head hitlist;
174 struct sk_buff *skb;
175
176 /*
177 * Avoid a recursive GC.
178 */
179
180 if (down_trylock(&unix_gc_sem))
181 return;
182
183 read_lock(&unix_table_lock);
184
185 forall_unix_sockets(i, s)
186 {
187 s->protinfo.af_unix.gc_tree=GC_ORPHAN;
188 }
189 /*
190 * Everything is now marked
191 */
192
193 /* Invariant to be maintained:
194 - everything unmarked is either:
195 -- (a) on the stack, or
196 -- (b) has all of its children unmarked
197 - everything on the stack is always unmarked
198 - nothing is ever pushed onto the stack twice, because:
199 -- nothing previously unmarked is ever pushed on the stack
200 */
201
202 /*
203 * Push root set
204 */
205
206 forall_unix_sockets(i, s)
207 {
208 /*
209 * If all instances of the descriptor are not
210 * in flight we are in use.
211 */
212 if(s->socket && s->socket->file &&
213 file_count(s->socket->file) > atomic_read(&s->protinfo.af_unix.inflight))
214 maybe_unmark_and_push(s);
215 }
216
217 /*
218 * Mark phase
219 */
220
221 while (!empty_stack())
222 {
223 unix_socket *x = pop_stack();
224 unix_socket *sk;
225
226 spin_lock(&x->receive_queue.lock);
227 skb=skb_peek(&x->receive_queue);
228
229 /*
230 * Loop through all but first born
231 */
232
233 while(skb && skb != (struct sk_buff *)&x->receive_queue)
234 {
235 /*
236 * Do we have file descriptors ?
237 */
238 if(UNIXCB(skb).fp)
239 {
240 /*
241 * Process the descriptors of this socket
242 */
243 int nfd=UNIXCB(skb).fp->count;
244 struct file **fp = UNIXCB(skb).fp->fp;
245 while(nfd--)
246 {
247 /*
248 * Get the socket the fd matches if
249 * it indeed does so
250 */
251 if((sk=unix_get_socket(*fp++))!=NULL)
252 {
253 maybe_unmark_and_push(sk);
254 }
255 }
256 }
257 /* We have to scan not-yet-accepted ones too */
258 if (x->state == TCP_LISTEN) {
259 maybe_unmark_and_push(skb->sk);
260 }
261 skb=skb->next;
262 }
263 spin_unlock(&x->receive_queue.lock);
264 sock_put(x);
265 }
266
267 skb_queue_head_init(&hitlist);
268
269 forall_unix_sockets(i, s)
270 {
271 if (s->protinfo.af_unix.gc_tree == GC_ORPHAN)
272 {
273 struct sk_buff *nextsk;
274 spin_lock(&s->receive_queue.lock);
275 skb=skb_peek(&s->receive_queue);
276 while(skb && skb != (struct sk_buff *)&s->receive_queue)
277 {
278 nextsk=skb->next;
279 /*
280 * Do we have file descriptors ?
281 */
282 if(UNIXCB(skb).fp)
283 {
284 __skb_unlink(skb, skb->list);
285 __skb_queue_tail(&hitlist,skb);
286 }
287 skb=nextsk;
288 }
289 spin_unlock(&s->receive_queue.lock);
290 }
291 s->protinfo.af_unix.gc_tree = GC_ORPHAN;
292 }
293 read_unlock(&unix_table_lock);
294
295 /*
296 * Here we are. Hitlist is filled. Die.
297 */
298
299 while ((skb=__skb_dequeue(&hitlist))!=NULL) {
300 kfree_skb(skb);
301 }
302
303 up(&unix_gc_sem);
304 }
305
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