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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
91static LIST_HEAD(gc_inflight_list);
92static LIST_HEAD(gc_candidates);
93static DEFINE_SPINLOCK(unix_gc_lock);
94static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
95
96unsigned int unix_tot_inflight;
97
98struct sock *unix_get_socket(struct file *filp)
99{
100 struct sock *u_sock = NULL;
101 struct inode *inode = file_inode(filp);
102
103 /* Socket ? */
104 if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
105 struct socket *sock = SOCKET_I(inode);
106 struct sock *s = sock->sk;
107
108 /* PF_UNIX ? */
109 if (s && sock->ops && sock->ops->family == PF_UNIX)
110 u_sock = s;
111 }
112 return u_sock;
113}
114
115/* Keep the number of times in flight count for the file
116 * descriptor if it is for an AF_UNIX socket.
117 */
118
119void unix_inflight(struct user_struct *user, struct file *fp)
120{
121 struct sock *s = unix_get_socket(fp);
122
123 spin_lock(&unix_gc_lock);
124
125 if (s) {
126 struct unix_sock *u = unix_sk(s);
127
128 if (atomic_long_inc_return(&u->inflight) == 1) {
129 BUG_ON(!list_empty(&u->link));
130 list_add_tail(&u->link, &gc_inflight_list);
131 } else {
132 BUG_ON(list_empty(&u->link));
133 }
134 unix_tot_inflight++;
135 }
136 user->unix_inflight++;
137 spin_unlock(&unix_gc_lock);
138}
139
140void unix_notinflight(struct user_struct *user, struct file *fp)
141{
142 struct sock *s = unix_get_socket(fp);
143
144 spin_lock(&unix_gc_lock);
145
146 if (s) {
147 struct unix_sock *u = unix_sk(s);
148
149 BUG_ON(list_empty(&u->link));
150
151 if (atomic_long_dec_and_test(&u->inflight))
152 list_del_init(&u->link);
153 unix_tot_inflight--;
154 }
155 user->unix_inflight--;
156 spin_unlock(&unix_gc_lock);
157}
158
159static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
160 struct sk_buff_head *hitlist)
161{
162 struct sk_buff *skb;
163 struct sk_buff *next;
164
165 spin_lock(&x->sk_receive_queue.lock);
166 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
167 /* Do we have file descriptors ? */
168 if (UNIXCB(skb).fp) {
169 bool hit = false;
170 /* Process the descriptors of this socket */
171 int nfd = UNIXCB(skb).fp->count;
172 struct file **fp = UNIXCB(skb).fp->fp;
173
174 while (nfd--) {
175 /* Get the socket the fd matches if it indeed does so */
176 struct sock *sk = unix_get_socket(*fp++);
177
178 if (sk) {
179 struct unix_sock *u = unix_sk(sk);
180
181 /* Ignore non-candidates, they could
182 * have been added to the queues after
183 * starting the garbage collection
184 */
185 if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
186 hit = true;
187
188 func(u);
189 }
190 }
191 }
192 if (hit && hitlist != NULL) {
193 __skb_unlink(skb, &x->sk_receive_queue);
194 __skb_queue_tail(hitlist, skb);
195 }
196 }
197 }
198 spin_unlock(&x->sk_receive_queue.lock);
199}
200
201static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
202 struct sk_buff_head *hitlist)
203{
204 if (x->sk_state != TCP_LISTEN) {
205 scan_inflight(x, func, hitlist);
206 } else {
207 struct sk_buff *skb;
208 struct sk_buff *next;
209 struct unix_sock *u;
210 LIST_HEAD(embryos);
211
212 /* For a listening socket collect the queued embryos
213 * and perform a scan on them as well.
214 */
215 spin_lock(&x->sk_receive_queue.lock);
216 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
217 u = unix_sk(skb->sk);
218
219 /* An embryo cannot be in-flight, so it's safe
220 * to use the list link.
221 */
222 BUG_ON(!list_empty(&u->link));
223 list_add_tail(&u->link, &embryos);
224 }
225 spin_unlock(&x->sk_receive_queue.lock);
226
227 while (!list_empty(&embryos)) {
228 u = list_entry(embryos.next, struct unix_sock, link);
229 scan_inflight(&u->sk, func, hitlist);
230 list_del_init(&u->link);
231 }
232 }
233}
234
235static void dec_inflight(struct unix_sock *usk)
236{
237 atomic_long_dec(&usk->inflight);
238}
239
240static void inc_inflight(struct unix_sock *usk)
241{
242 atomic_long_inc(&usk->inflight);
243}
244
245static void inc_inflight_move_tail(struct unix_sock *u)
246{
247 atomic_long_inc(&u->inflight);
248 /* If this still might be part of a cycle, move it to the end
249 * of the list, so that it's checked even if it was already
250 * passed over
251 */
252 if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
253 list_move_tail(&u->link, &gc_candidates);
254}
255
256static bool gc_in_progress;
257#define UNIX_INFLIGHT_TRIGGER_GC 16000
258
259void wait_for_unix_gc(void)
260{
261 /* If number of inflight sockets is insane,
262 * force a garbage collect right now.
263 */
264 if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
265 unix_gc();
266 wait_event(unix_gc_wait, gc_in_progress == false);
267}
268
269/* The external entry point: unix_gc() */
270void unix_gc(void)
271{
272 struct unix_sock *u;
273 struct unix_sock *next;
274 struct sk_buff_head hitlist;
275 struct list_head cursor;
276 LIST_HEAD(not_cycle_list);
277
278 spin_lock(&unix_gc_lock);
279
280 /* Avoid a recursive GC. */
281 if (gc_in_progress)
282 goto out;
283
284 gc_in_progress = true;
285 /* First, select candidates for garbage collection. Only
286 * in-flight sockets are considered, and from those only ones
287 * which don't have any external reference.
288 *
289 * Holding unix_gc_lock will protect these candidates from
290 * being detached, and hence from gaining an external
291 * reference. Since there are no possible receivers, all
292 * buffers currently on the candidates' queues stay there
293 * during the garbage collection.
294 *
295 * We also know that no new candidate can be added onto the
296 * receive queues. Other, non candidate sockets _can_ be
297 * added to queue, so we must make sure only to touch
298 * candidates.
299 */
300 list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
301 long total_refs;
302 long inflight_refs;
303
304 total_refs = file_count(u->sk.sk_socket->file);
305 inflight_refs = atomic_long_read(&u->inflight);
306
307 BUG_ON(inflight_refs < 1);
308 BUG_ON(total_refs < inflight_refs);
309 if (total_refs == inflight_refs) {
310 list_move_tail(&u->link, &gc_candidates);
311 __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
312 __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
313 }
314 }
315
316 /* Now remove all internal in-flight reference to children of
317 * the candidates.
318 */
319 list_for_each_entry(u, &gc_candidates, link)
320 scan_children(&u->sk, dec_inflight, NULL);
321
322 /* Restore the references for children of all candidates,
323 * which have remaining references. Do this recursively, so
324 * only those remain, which form cyclic references.
325 *
326 * Use a "cursor" link, to make the list traversal safe, even
327 * though elements might be moved about.
328 */
329 list_add(&cursor, &gc_candidates);
330 while (cursor.next != &gc_candidates) {
331 u = list_entry(cursor.next, struct unix_sock, link);
332
333 /* Move cursor to after the current position. */
334 list_move(&cursor, &u->link);
335
336 if (atomic_long_read(&u->inflight) > 0) {
337 list_move_tail(&u->link, ¬_cycle_list);
338 __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
339 scan_children(&u->sk, inc_inflight_move_tail, NULL);
340 }
341 }
342 list_del(&cursor);
343
344 /* not_cycle_list contains those sockets which do not make up a
345 * cycle. Restore these to the inflight list.
346 */
347 while (!list_empty(¬_cycle_list)) {
348 u = list_entry(not_cycle_list.next, struct unix_sock, link);
349 __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
350 list_move_tail(&u->link, &gc_inflight_list);
351 }
352
353 /* Now gc_candidates contains only garbage. Restore original
354 * inflight counters for these as well, and remove the skbuffs
355 * which are creating the cycle(s).
356 */
357 skb_queue_head_init(&hitlist);
358 list_for_each_entry(u, &gc_candidates, link)
359 scan_children(&u->sk, inc_inflight, &hitlist);
360
361 spin_unlock(&unix_gc_lock);
362
363 /* Here we are. Hitlist is filled. Die. */
364 __skb_queue_purge(&hitlist);
365
366 spin_lock(&unix_gc_lock);
367
368 /* All candidates should have been detached by now. */
369 BUG_ON(!list_empty(&gc_candidates));
370 gc_in_progress = false;
371 wake_up(&unix_gc_wait);
372
373 out:
374 spin_unlock(&unix_gc_lock);
375}
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * NET3: Garbage Collector For AF_UNIX sockets
4 *
5 * Garbage Collector:
6 * Copyright (C) Barak A. Pearlmutter.
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 * Fixes:
28 * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed.
29 * Cope with changing max_files.
30 * Al Viro 11 Oct 1998
31 * Graph may have cycles. That is, we can send the descriptor
32 * of foo to bar and vice versa. Current code chokes on that.
33 * Fix: move SCM_RIGHTS ones into the separate list and then
34 * skb_free() them all instead of doing explicit fput's.
35 * Another problem: since fput() may block somebody may
36 * create a new unix_socket when we are in the middle of sweep
37 * phase. Fix: revert the logic wrt MARKED. Mark everything
38 * upon the beginning and unmark non-junk ones.
39 *
40 * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS
41 * sent to connect()'ed but still not accept()'ed sockets.
42 * Fixed. Old code had slightly different problem here:
43 * extra fput() in situation when we passed the descriptor via
44 * such socket and closed it (descriptor). That would happen on
45 * each unix_gc() until the accept(). Since the struct file in
46 * question would go to the free list and might be reused...
47 * That might be the reason of random oopses on filp_close()
48 * in unrelated processes.
49 *
50 * AV 28 Feb 1999
51 * Kill the explicit allocation of stack. Now we keep the tree
52 * with root in dummy + pointer (gc_current) to one of the nodes.
53 * Stack is represented as path from gc_current to dummy. Unmark
54 * now means "add to tree". Push == "make it a son of gc_current".
55 * Pop == "move gc_current to parent". We keep only pointers to
56 * parents (->gc_tree).
57 * AV 1 Mar 1999
58 * Damn. Added missing check for ->dead in listen queues scanning.
59 *
60 * Miklos Szeredi 25 Jun 2007
61 * Reimplement with a cycle collecting algorithm. This should
62 * solve several problems with the previous code, like being racy
63 * wrt receive and holding up unrelated socket operations.
64 */
65
66#include <linux/kernel.h>
67#include <linux/string.h>
68#include <linux/socket.h>
69#include <linux/un.h>
70#include <linux/net.h>
71#include <linux/fs.h>
72#include <linux/skbuff.h>
73#include <linux/netdevice.h>
74#include <linux/file.h>
75#include <linux/proc_fs.h>
76#include <linux/mutex.h>
77#include <linux/wait.h>
78
79#include <net/sock.h>
80#include <net/af_unix.h>
81#include <net/scm.h>
82#include <net/tcp_states.h>
83
84struct unix_sock *unix_get_socket(struct file *filp)
85{
86 struct inode *inode = file_inode(filp);
87
88 /* Socket ? */
89 if (S_ISSOCK(inode->i_mode) && !(filp->f_mode & FMODE_PATH)) {
90 struct socket *sock = SOCKET_I(inode);
91 const struct proto_ops *ops;
92 struct sock *sk = sock->sk;
93
94 ops = READ_ONCE(sock->ops);
95
96 /* PF_UNIX ? */
97 if (sk && ops && ops->family == PF_UNIX)
98 return unix_sk(sk);
99 }
100
101 return NULL;
102}
103
104DEFINE_SPINLOCK(unix_gc_lock);
105unsigned int unix_tot_inflight;
106static LIST_HEAD(gc_candidates);
107static LIST_HEAD(gc_inflight_list);
108
109/* Keep the number of times in flight count for the file
110 * descriptor if it is for an AF_UNIX socket.
111 */
112void unix_inflight(struct user_struct *user, struct file *filp)
113{
114 struct unix_sock *u = unix_get_socket(filp);
115
116 spin_lock(&unix_gc_lock);
117
118 if (u) {
119 if (!u->inflight) {
120 WARN_ON_ONCE(!list_empty(&u->link));
121 list_add_tail(&u->link, &gc_inflight_list);
122 } else {
123 WARN_ON_ONCE(list_empty(&u->link));
124 }
125 u->inflight++;
126
127 /* Paired with READ_ONCE() in wait_for_unix_gc() */
128 WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + 1);
129 }
130
131 WRITE_ONCE(user->unix_inflight, user->unix_inflight + 1);
132
133 spin_unlock(&unix_gc_lock);
134}
135
136void unix_notinflight(struct user_struct *user, struct file *filp)
137{
138 struct unix_sock *u = unix_get_socket(filp);
139
140 spin_lock(&unix_gc_lock);
141
142 if (u) {
143 WARN_ON_ONCE(!u->inflight);
144 WARN_ON_ONCE(list_empty(&u->link));
145
146 u->inflight--;
147 if (!u->inflight)
148 list_del_init(&u->link);
149
150 /* Paired with READ_ONCE() in wait_for_unix_gc() */
151 WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - 1);
152 }
153
154 WRITE_ONCE(user->unix_inflight, user->unix_inflight - 1);
155
156 spin_unlock(&unix_gc_lock);
157}
158
159static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
160 struct sk_buff_head *hitlist)
161{
162 struct sk_buff *skb;
163 struct sk_buff *next;
164
165 spin_lock(&x->sk_receive_queue.lock);
166 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
167 /* Do we have file descriptors ? */
168 if (UNIXCB(skb).fp) {
169 bool hit = false;
170 /* Process the descriptors of this socket */
171 int nfd = UNIXCB(skb).fp->count;
172 struct file **fp = UNIXCB(skb).fp->fp;
173
174 while (nfd--) {
175 /* Get the socket the fd matches if it indeed does so */
176 struct unix_sock *u = unix_get_socket(*fp++);
177
178 /* Ignore non-candidates, they could have been added
179 * to the queues after starting the garbage collection
180 */
181 if (u && test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
182 hit = true;
183
184 func(u);
185 }
186 }
187 if (hit && hitlist != NULL) {
188 __skb_unlink(skb, &x->sk_receive_queue);
189 __skb_queue_tail(hitlist, skb);
190 }
191 }
192 }
193 spin_unlock(&x->sk_receive_queue.lock);
194}
195
196static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
197 struct sk_buff_head *hitlist)
198{
199 if (x->sk_state != TCP_LISTEN) {
200 scan_inflight(x, func, hitlist);
201 } else {
202 struct sk_buff *skb;
203 struct sk_buff *next;
204 struct unix_sock *u;
205 LIST_HEAD(embryos);
206
207 /* For a listening socket collect the queued embryos
208 * and perform a scan on them as well.
209 */
210 spin_lock(&x->sk_receive_queue.lock);
211 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
212 u = unix_sk(skb->sk);
213
214 /* An embryo cannot be in-flight, so it's safe
215 * to use the list link.
216 */
217 WARN_ON_ONCE(!list_empty(&u->link));
218 list_add_tail(&u->link, &embryos);
219 }
220 spin_unlock(&x->sk_receive_queue.lock);
221
222 while (!list_empty(&embryos)) {
223 u = list_entry(embryos.next, struct unix_sock, link);
224 scan_inflight(&u->sk, func, hitlist);
225 list_del_init(&u->link);
226 }
227 }
228}
229
230static void dec_inflight(struct unix_sock *usk)
231{
232 usk->inflight--;
233}
234
235static void inc_inflight(struct unix_sock *usk)
236{
237 usk->inflight++;
238}
239
240static void inc_inflight_move_tail(struct unix_sock *u)
241{
242 u->inflight++;
243
244 /* If this still might be part of a cycle, move it to the end
245 * of the list, so that it's checked even if it was already
246 * passed over
247 */
248 if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
249 list_move_tail(&u->link, &gc_candidates);
250}
251
252static bool gc_in_progress;
253
254static void __unix_gc(struct work_struct *work)
255{
256 struct sk_buff_head hitlist;
257 struct unix_sock *u, *next;
258 LIST_HEAD(not_cycle_list);
259 struct list_head cursor;
260
261 spin_lock(&unix_gc_lock);
262
263 /* First, select candidates for garbage collection. Only
264 * in-flight sockets are considered, and from those only ones
265 * which don't have any external reference.
266 *
267 * Holding unix_gc_lock will protect these candidates from
268 * being detached, and hence from gaining an external
269 * reference. Since there are no possible receivers, all
270 * buffers currently on the candidates' queues stay there
271 * during the garbage collection.
272 *
273 * We also know that no new candidate can be added onto the
274 * receive queues. Other, non candidate sockets _can_ be
275 * added to queue, so we must make sure only to touch
276 * candidates.
277 *
278 * Embryos, though never candidates themselves, affect which
279 * candidates are reachable by the garbage collector. Before
280 * being added to a listener's queue, an embryo may already
281 * receive data carrying SCM_RIGHTS, potentially making the
282 * passed socket a candidate that is not yet reachable by the
283 * collector. It becomes reachable once the embryo is
284 * enqueued. Therefore, we must ensure that no SCM-laden
285 * embryo appears in a (candidate) listener's queue between
286 * consecutive scan_children() calls.
287 */
288 list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
289 struct sock *sk = &u->sk;
290 long total_refs;
291
292 total_refs = file_count(sk->sk_socket->file);
293
294 WARN_ON_ONCE(!u->inflight);
295 WARN_ON_ONCE(total_refs < u->inflight);
296 if (total_refs == u->inflight) {
297 list_move_tail(&u->link, &gc_candidates);
298 __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
299 __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
300
301 if (sk->sk_state == TCP_LISTEN) {
302 unix_state_lock_nested(sk, U_LOCK_GC_LISTENER);
303 unix_state_unlock(sk);
304 }
305 }
306 }
307
308 /* Now remove all internal in-flight reference to children of
309 * the candidates.
310 */
311 list_for_each_entry(u, &gc_candidates, link)
312 scan_children(&u->sk, dec_inflight, NULL);
313
314 /* Restore the references for children of all candidates,
315 * which have remaining references. Do this recursively, so
316 * only those remain, which form cyclic references.
317 *
318 * Use a "cursor" link, to make the list traversal safe, even
319 * though elements might be moved about.
320 */
321 list_add(&cursor, &gc_candidates);
322 while (cursor.next != &gc_candidates) {
323 u = list_entry(cursor.next, struct unix_sock, link);
324
325 /* Move cursor to after the current position. */
326 list_move(&cursor, &u->link);
327
328 if (u->inflight) {
329 list_move_tail(&u->link, ¬_cycle_list);
330 __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
331 scan_children(&u->sk, inc_inflight_move_tail, NULL);
332 }
333 }
334 list_del(&cursor);
335
336 /* Now gc_candidates contains only garbage. Restore original
337 * inflight counters for these as well, and remove the skbuffs
338 * which are creating the cycle(s).
339 */
340 skb_queue_head_init(&hitlist);
341 list_for_each_entry(u, &gc_candidates, link) {
342 scan_children(&u->sk, inc_inflight, &hitlist);
343
344#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
345 if (u->oob_skb) {
346 kfree_skb(u->oob_skb);
347 u->oob_skb = NULL;
348 }
349#endif
350 }
351
352 /* not_cycle_list contains those sockets which do not make up a
353 * cycle. Restore these to the inflight list.
354 */
355 while (!list_empty(¬_cycle_list)) {
356 u = list_entry(not_cycle_list.next, struct unix_sock, link);
357 __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
358 list_move_tail(&u->link, &gc_inflight_list);
359 }
360
361 spin_unlock(&unix_gc_lock);
362
363 /* Here we are. Hitlist is filled. Die. */
364 __skb_queue_purge(&hitlist);
365
366 spin_lock(&unix_gc_lock);
367
368 /* All candidates should have been detached by now. */
369 WARN_ON_ONCE(!list_empty(&gc_candidates));
370
371 /* Paired with READ_ONCE() in wait_for_unix_gc(). */
372 WRITE_ONCE(gc_in_progress, false);
373
374 spin_unlock(&unix_gc_lock);
375}
376
377static DECLARE_WORK(unix_gc_work, __unix_gc);
378
379void unix_gc(void)
380{
381 WRITE_ONCE(gc_in_progress, true);
382 queue_work(system_unbound_wq, &unix_gc_work);
383}
384
385#define UNIX_INFLIGHT_TRIGGER_GC 16000
386#define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)
387
388void wait_for_unix_gc(struct scm_fp_list *fpl)
389{
390 /* If number of inflight sockets is insane,
391 * force a garbage collect right now.
392 *
393 * Paired with the WRITE_ONCE() in unix_inflight(),
394 * unix_notinflight(), and __unix_gc().
395 */
396 if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
397 !READ_ONCE(gc_in_progress))
398 unix_gc();
399
400 /* Penalise users who want to send AF_UNIX sockets
401 * but whose sockets have not been received yet.
402 */
403 if (!fpl || !fpl->count_unix ||
404 READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
405 return;
406
407 if (READ_ONCE(gc_in_progress))
408 flush_work(&unix_gc_work);
409}