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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
84#include "scm.h"
85
86/* Internal data structures and random procedures: */
87
88static LIST_HEAD(gc_candidates);
89static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
90
91static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
92 struct sk_buff_head *hitlist)
93{
94 struct sk_buff *skb;
95 struct sk_buff *next;
96
97 spin_lock(&x->sk_receive_queue.lock);
98 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
99 /* Do we have file descriptors ? */
100 if (UNIXCB(skb).fp) {
101 bool hit = false;
102 /* Process the descriptors of this socket */
103 int nfd = UNIXCB(skb).fp->count;
104 struct file **fp = UNIXCB(skb).fp->fp;
105
106 while (nfd--) {
107 /* Get the socket the fd matches if it indeed does so */
108 struct sock *sk = unix_get_socket(*fp++);
109
110 if (sk) {
111 struct unix_sock *u = unix_sk(sk);
112
113 /* Ignore non-candidates, they could
114 * have been added to the queues after
115 * starting the garbage collection
116 */
117 if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) {
118 hit = true;
119
120 func(u);
121 }
122 }
123 }
124 if (hit && hitlist != NULL) {
125 __skb_unlink(skb, &x->sk_receive_queue);
126 __skb_queue_tail(hitlist, skb);
127 }
128 }
129 }
130 spin_unlock(&x->sk_receive_queue.lock);
131}
132
133static void scan_children(struct sock *x, void (*func)(struct unix_sock *),
134 struct sk_buff_head *hitlist)
135{
136 if (x->sk_state != TCP_LISTEN) {
137 scan_inflight(x, func, hitlist);
138 } else {
139 struct sk_buff *skb;
140 struct sk_buff *next;
141 struct unix_sock *u;
142 LIST_HEAD(embryos);
143
144 /* For a listening socket collect the queued embryos
145 * and perform a scan on them as well.
146 */
147 spin_lock(&x->sk_receive_queue.lock);
148 skb_queue_walk_safe(&x->sk_receive_queue, skb, next) {
149 u = unix_sk(skb->sk);
150
151 /* An embryo cannot be in-flight, so it's safe
152 * to use the list link.
153 */
154 BUG_ON(!list_empty(&u->link));
155 list_add_tail(&u->link, &embryos);
156 }
157 spin_unlock(&x->sk_receive_queue.lock);
158
159 while (!list_empty(&embryos)) {
160 u = list_entry(embryos.next, struct unix_sock, link);
161 scan_inflight(&u->sk, func, hitlist);
162 list_del_init(&u->link);
163 }
164 }
165}
166
167static void dec_inflight(struct unix_sock *usk)
168{
169 atomic_long_dec(&usk->inflight);
170}
171
172static void inc_inflight(struct unix_sock *usk)
173{
174 atomic_long_inc(&usk->inflight);
175}
176
177static void inc_inflight_move_tail(struct unix_sock *u)
178{
179 atomic_long_inc(&u->inflight);
180 /* If this still might be part of a cycle, move it to the end
181 * of the list, so that it's checked even if it was already
182 * passed over
183 */
184 if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags))
185 list_move_tail(&u->link, &gc_candidates);
186}
187
188static bool gc_in_progress;
189#define UNIX_INFLIGHT_TRIGGER_GC 16000
190
191void wait_for_unix_gc(void)
192{
193 /* If number of inflight sockets is insane,
194 * force a garbage collect right now.
195 * Paired with the WRITE_ONCE() in unix_inflight(),
196 * unix_notinflight() and gc_in_progress().
197 */
198 if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
199 !READ_ONCE(gc_in_progress))
200 unix_gc();
201 wait_event(unix_gc_wait, gc_in_progress == false);
202}
203
204/* The external entry point: unix_gc() */
205void unix_gc(void)
206{
207 struct sk_buff *next_skb, *skb;
208 struct unix_sock *u;
209 struct unix_sock *next;
210 struct sk_buff_head hitlist;
211 struct list_head cursor;
212 LIST_HEAD(not_cycle_list);
213
214 spin_lock(&unix_gc_lock);
215
216 /* Avoid a recursive GC. */
217 if (gc_in_progress)
218 goto out;
219
220 /* Paired with READ_ONCE() in wait_for_unix_gc(). */
221 WRITE_ONCE(gc_in_progress, true);
222
223 /* First, select candidates for garbage collection. Only
224 * in-flight sockets are considered, and from those only ones
225 * which don't have any external reference.
226 *
227 * Holding unix_gc_lock will protect these candidates from
228 * being detached, and hence from gaining an external
229 * reference. Since there are no possible receivers, all
230 * buffers currently on the candidates' queues stay there
231 * during the garbage collection.
232 *
233 * We also know that no new candidate can be added onto the
234 * receive queues. Other, non candidate sockets _can_ be
235 * added to queue, so we must make sure only to touch
236 * candidates.
237 */
238 list_for_each_entry_safe(u, next, &gc_inflight_list, link) {
239 long total_refs;
240 long inflight_refs;
241
242 total_refs = file_count(u->sk.sk_socket->file);
243 inflight_refs = atomic_long_read(&u->inflight);
244
245 BUG_ON(inflight_refs < 1);
246 BUG_ON(total_refs < inflight_refs);
247 if (total_refs == inflight_refs) {
248 list_move_tail(&u->link, &gc_candidates);
249 __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
250 __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
251 }
252 }
253
254 /* Now remove all internal in-flight reference to children of
255 * the candidates.
256 */
257 list_for_each_entry(u, &gc_candidates, link)
258 scan_children(&u->sk, dec_inflight, NULL);
259
260 /* Restore the references for children of all candidates,
261 * which have remaining references. Do this recursively, so
262 * only those remain, which form cyclic references.
263 *
264 * Use a "cursor" link, to make the list traversal safe, even
265 * though elements might be moved about.
266 */
267 list_add(&cursor, &gc_candidates);
268 while (cursor.next != &gc_candidates) {
269 u = list_entry(cursor.next, struct unix_sock, link);
270
271 /* Move cursor to after the current position. */
272 list_move(&cursor, &u->link);
273
274 if (atomic_long_read(&u->inflight) > 0) {
275 list_move_tail(&u->link, ¬_cycle_list);
276 __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags);
277 scan_children(&u->sk, inc_inflight_move_tail, NULL);
278 }
279 }
280 list_del(&cursor);
281
282 /* Now gc_candidates contains only garbage. Restore original
283 * inflight counters for these as well, and remove the skbuffs
284 * which are creating the cycle(s).
285 */
286 skb_queue_head_init(&hitlist);
287 list_for_each_entry(u, &gc_candidates, link) {
288 scan_children(&u->sk, inc_inflight, &hitlist);
289
290#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
291 if (u->oob_skb) {
292 kfree_skb(u->oob_skb);
293 u->oob_skb = NULL;
294 }
295#endif
296 }
297
298 /* not_cycle_list contains those sockets which do not make up a
299 * cycle. Restore these to the inflight list.
300 */
301 while (!list_empty(¬_cycle_list)) {
302 u = list_entry(not_cycle_list.next, struct unix_sock, link);
303 __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags);
304 list_move_tail(&u->link, &gc_inflight_list);
305 }
306
307 spin_unlock(&unix_gc_lock);
308
309 /* We need io_uring to clean its registered files, ignore all io_uring
310 * originated skbs. It's fine as io_uring doesn't keep references to
311 * other io_uring instances and so killing all other files in the cycle
312 * will put all io_uring references forcing it to go through normal
313 * release.path eventually putting registered files.
314 */
315 skb_queue_walk_safe(&hitlist, skb, next_skb) {
316 if (skb->destructor == io_uring_destruct_scm) {
317 __skb_unlink(skb, &hitlist);
318 skb_queue_tail(&skb->sk->sk_receive_queue, skb);
319 }
320 }
321
322 /* Here we are. Hitlist is filled. Die. */
323 __skb_queue_purge(&hitlist);
324
325 spin_lock(&unix_gc_lock);
326
327 /* There could be io_uring registered files, just push them back to
328 * the inflight list
329 */
330 list_for_each_entry_safe(u, next, &gc_candidates, link)
331 list_move_tail(&u->link, &gc_inflight_list);
332
333 /* All candidates should have been detached by now. */
334 BUG_ON(!list_empty(&gc_candidates));
335
336 /* Paired with READ_ONCE() in wait_for_unix_gc(). */
337 WRITE_ONCE(gc_in_progress, false);
338
339 wake_up(&unix_gc_wait);
340
341 out:
342 spin_unlock(&unix_gc_lock);
343}
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}