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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 | * Miklos Szeredi 25 Jun 2007 |
66 | * Reimplement with a cycle collecting algorithm. This should |
67 | * solve several problems with the previous code, like being racy |
68 | * wrt receive and holding up unrelated socket operations. |
69 | */ |
70 | |
71 | #include <linux/kernel.h> |
72 | #include <linux/string.h> |
73 | #include <linux/socket.h> |
74 | #include <linux/un.h> |
75 | #include <linux/net.h> |
76 | #include <linux/fs.h> |
77 | #include <linux/skbuff.h> |
78 | #include <linux/netdevice.h> |
79 | #include <linux/file.h> |
80 | #include <linux/proc_fs.h> |
81 | #include <linux/mutex.h> |
82 | #include <linux/wait.h> |
83 | |
84 | #include <net/sock.h> |
85 | #include <net/af_unix.h> |
86 | #include <net/scm.h> |
87 | #include <net/tcp_states.h> |
88 | |
89 | /* Internal data structures and random procedures: */ |
90 | |
91 | static LIST_HEAD(gc_inflight_list); |
92 | static LIST_HEAD(gc_candidates); |
93 | static DEFINE_SPINLOCK(unix_gc_lock); |
94 | static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait); |
95 | |
96 | unsigned int unix_tot_inflight; |
97 | |
98 | |
99 | static struct sock *unix_get_socket(struct file *filp) |
100 | { |
101 | struct sock *u_sock = NULL; |
102 | struct inode *inode = filp->f_path.dentry->d_inode; |
103 | |
104 | /* |
105 | * Socket ? |
106 | */ |
107 | if (S_ISSOCK(inode->i_mode)) { |
108 | struct socket *sock = SOCKET_I(inode); |
109 | struct sock *s = sock->sk; |
110 | |
111 | /* |
112 | * PF_UNIX ? |
113 | */ |
114 | if (s && sock->ops && sock->ops->family == PF_UNIX) |
115 | u_sock = s; |
116 | } |
117 | return u_sock; |
118 | } |
119 | |
120 | /* |
121 | * Keep the number of times in flight count for the file |
122 | * descriptor if it is for an AF_UNIX socket. |
123 | */ |
124 | |
125 | void unix_inflight(struct file *fp) |
126 | { |
127 | struct sock *s = unix_get_socket(fp); |
128 | if (s) { |
129 | struct unix_sock *u = unix_sk(s); |
130 | spin_lock(&unix_gc_lock); |
131 | if (atomic_long_inc_return(&u->inflight) == 1) { |
132 | BUG_ON(!list_empty(&u->link)); |
133 | list_add_tail(&u->link, &gc_inflight_list); |
134 | } else { |
135 | BUG_ON(list_empty(&u->link)); |
136 | } |
137 | unix_tot_inflight++; |
138 | spin_unlock(&unix_gc_lock); |
139 | } |
140 | } |
141 | |
142 | void unix_notinflight(struct file *fp) |
143 | { |
144 | struct sock *s = unix_get_socket(fp); |
145 | if (s) { |
146 | struct unix_sock *u = unix_sk(s); |
147 | spin_lock(&unix_gc_lock); |
148 | BUG_ON(list_empty(&u->link)); |
149 | if (atomic_long_dec_and_test(&u->inflight)) |
150 | list_del_init(&u->link); |
151 | unix_tot_inflight--; |
152 | spin_unlock(&unix_gc_lock); |
153 | } |
154 | } |
155 | |
156 | static inline struct sk_buff *sock_queue_head(struct sock *sk) |
157 | { |
158 | return (struct sk_buff *)&sk->sk_receive_queue; |
159 | } |
160 | |
161 | #define receive_queue_for_each_skb(sk, next, skb) \ |
162 | for (skb = sock_queue_head(sk)->next, next = skb->next; \ |
163 | skb != sock_queue_head(sk); skb = next, next = skb->next) |
164 | |
165 | static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *), |
166 | struct sk_buff_head *hitlist) |
167 | { |
168 | struct sk_buff *skb; |
169 | struct sk_buff *next; |
170 | |
171 | spin_lock(&x->sk_receive_queue.lock); |
172 | receive_queue_for_each_skb(x, next, skb) { |
173 | /* |
174 | * Do we have file descriptors ? |
175 | */ |
176 | if (UNIXCB(skb).fp) { |
177 | bool hit = false; |
178 | /* |
179 | * Process the descriptors of this socket |
180 | */ |
181 | int nfd = UNIXCB(skb).fp->count; |
182 | struct file **fp = UNIXCB(skb).fp->fp; |
183 | while (nfd--) { |
184 | /* |
185 | * Get the socket the fd matches |
186 | * if it indeed does so |
187 | */ |
188 | struct sock *sk = unix_get_socket(*fp++); |
189 | if (sk) { |
190 | struct unix_sock *u = unix_sk(sk); |
191 | |
192 | /* |
193 | * Ignore non-candidates, they could |
194 | * have been added to the queues after |
195 | * starting the garbage collection |
196 | */ |
197 | if (u->gc_candidate) { |
198 | hit = true; |
199 | func(u); |
200 | } |
201 | } |
202 | } |
203 | if (hit && hitlist != NULL) { |
204 | __skb_unlink(skb, &x->sk_receive_queue); |
205 | __skb_queue_tail(hitlist, skb); |
206 | } |
207 | } |
208 | } |
209 | spin_unlock(&x->sk_receive_queue.lock); |
210 | } |
211 | |
212 | static void scan_children(struct sock *x, void (*func)(struct unix_sock *), |
213 | struct sk_buff_head *hitlist) |
214 | { |
215 | if (x->sk_state != TCP_LISTEN) |
216 | scan_inflight(x, func, hitlist); |
217 | else { |
218 | struct sk_buff *skb; |
219 | struct sk_buff *next; |
220 | struct unix_sock *u; |
221 | LIST_HEAD(embryos); |
222 | |
223 | /* |
224 | * For a listening socket collect the queued embryos |
225 | * and perform a scan on them as well. |
226 | */ |
227 | spin_lock(&x->sk_receive_queue.lock); |
228 | receive_queue_for_each_skb(x, next, skb) { |
229 | u = unix_sk(skb->sk); |
230 | |
231 | /* |
232 | * An embryo cannot be in-flight, so it's safe |
233 | * to use the list link. |
234 | */ |
235 | BUG_ON(!list_empty(&u->link)); |
236 | list_add_tail(&u->link, &embryos); |
237 | } |
238 | spin_unlock(&x->sk_receive_queue.lock); |
239 | |
240 | while (!list_empty(&embryos)) { |
241 | u = list_entry(embryos.next, struct unix_sock, link); |
242 | scan_inflight(&u->sk, func, hitlist); |
243 | list_del_init(&u->link); |
244 | } |
245 | } |
246 | } |
247 | |
248 | static void dec_inflight(struct unix_sock *usk) |
249 | { |
250 | atomic_long_dec(&usk->inflight); |
251 | } |
252 | |
253 | static void inc_inflight(struct unix_sock *usk) |
254 | { |
255 | atomic_long_inc(&usk->inflight); |
256 | } |
257 | |
258 | static void inc_inflight_move_tail(struct unix_sock *u) |
259 | { |
260 | atomic_long_inc(&u->inflight); |
261 | /* |
262 | * If this still might be part of a cycle, move it to the end |
263 | * of the list, so that it's checked even if it was already |
264 | * passed over |
265 | */ |
266 | if (u->gc_maybe_cycle) |
267 | list_move_tail(&u->link, &gc_candidates); |
268 | } |
269 | |
270 | static bool gc_in_progress = false; |
271 | |
272 | void wait_for_unix_gc(void) |
273 | { |
274 | wait_event(unix_gc_wait, gc_in_progress == false); |
275 | } |
276 | |
277 | /* The external entry point: unix_gc() */ |
278 | void unix_gc(void) |
279 | { |
280 | struct unix_sock *u; |
281 | struct unix_sock *next; |
282 | struct sk_buff_head hitlist; |
283 | struct list_head cursor; |
284 | LIST_HEAD(not_cycle_list); |
285 | |
286 | spin_lock(&unix_gc_lock); |
287 | |
288 | /* Avoid a recursive GC. */ |
289 | if (gc_in_progress) |
290 | goto out; |
291 | |
292 | gc_in_progress = true; |
293 | /* |
294 | * First, select candidates for garbage collection. Only |
295 | * in-flight sockets are considered, and from those only ones |
296 | * which don't have any external reference. |
297 | * |
298 | * Holding unix_gc_lock will protect these candidates from |
299 | * being detached, and hence from gaining an external |
300 | * reference. Since there are no possible receivers, all |
301 | * buffers currently on the candidates' queues stay there |
302 | * during the garbage collection. |
303 | * |
304 | * We also know that no new candidate can be added onto the |
305 | * receive queues. Other, non candidate sockets _can_ be |
306 | * added to queue, so we must make sure only to touch |
307 | * candidates. |
308 | */ |
309 | list_for_each_entry_safe(u, next, &gc_inflight_list, link) { |
310 | long total_refs; |
311 | long inflight_refs; |
312 | |
313 | total_refs = file_count(u->sk.sk_socket->file); |
314 | inflight_refs = atomic_long_read(&u->inflight); |
315 | |
316 | BUG_ON(inflight_refs < 1); |
317 | BUG_ON(total_refs < inflight_refs); |
318 | if (total_refs == inflight_refs) { |
319 | list_move_tail(&u->link, &gc_candidates); |
320 | u->gc_candidate = 1; |
321 | u->gc_maybe_cycle = 1; |
322 | } |
323 | } |
324 | |
325 | /* |
326 | * Now remove all internal in-flight reference to children of |
327 | * the candidates. |
328 | */ |
329 | list_for_each_entry(u, &gc_candidates, link) |
330 | scan_children(&u->sk, dec_inflight, NULL); |
331 | |
332 | /* |
333 | * Restore the references for children of all candidates, |
334 | * which have remaining references. Do this recursively, so |
335 | * only those remain, which form cyclic references. |
336 | * |
337 | * Use a "cursor" link, to make the list traversal safe, even |
338 | * though elements might be moved about. |
339 | */ |
340 | list_add(&cursor, &gc_candidates); |
341 | while (cursor.next != &gc_candidates) { |
342 | u = list_entry(cursor.next, struct unix_sock, link); |
343 | |
344 | /* Move cursor to after the current position. */ |
345 | list_move(&cursor, &u->link); |
346 | |
347 | if (atomic_long_read(&u->inflight) > 0) { |
348 | list_move_tail(&u->link, ¬_cycle_list); |
349 | u->gc_maybe_cycle = 0; |
350 | scan_children(&u->sk, inc_inflight_move_tail, NULL); |
351 | } |
352 | } |
353 | list_del(&cursor); |
354 | |
355 | /* |
356 | * not_cycle_list contains those sockets which do not make up a |
357 | * cycle. Restore these to the inflight list. |
358 | */ |
359 | while (!list_empty(¬_cycle_list)) { |
360 | u = list_entry(not_cycle_list.next, struct unix_sock, link); |
361 | u->gc_candidate = 0; |
362 | list_move_tail(&u->link, &gc_inflight_list); |
363 | } |
364 | |
365 | /* |
366 | * Now gc_candidates contains only garbage. Restore original |
367 | * inflight counters for these as well, and remove the skbuffs |
368 | * which are creating the cycle(s). |
369 | */ |
370 | skb_queue_head_init(&hitlist); |
371 | list_for_each_entry(u, &gc_candidates, link) |
372 | scan_children(&u->sk, inc_inflight, &hitlist); |
373 | |
374 | spin_unlock(&unix_gc_lock); |
375 | |
376 | /* Here we are. Hitlist is filled. Die. */ |
377 | __skb_queue_purge(&hitlist); |
378 | |
379 | spin_lock(&unix_gc_lock); |
380 | |
381 | /* All candidates should have been detached by now. */ |
382 | BUG_ON(!list_empty(&gc_candidates)); |
383 | gc_in_progress = false; |
384 | wake_up(&unix_gc_wait); |
385 | |
386 | out: |
387 | spin_unlock(&unix_gc_lock); |
388 | } |
389 |
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