| // SPDX-License-Identifier: GPL-2.0-or-later |
| /* |
| * NET3: Garbage Collector For AF_UNIX sockets |
| * |
| * Garbage Collector: |
| * Copyright (C) Barak A. Pearlmutter. |
| * |
| * Chopped about by Alan Cox 22/3/96 to make it fit the AF_UNIX socket problem. |
| * If it doesn't work blame me, it worked when Barak sent it. |
| * |
| * Assumptions: |
| * |
| * - object w/ a bit |
| * - free list |
| * |
| * Current optimizations: |
| * |
| * - explicit stack instead of recursion |
| * - tail recurse on first born instead of immediate push/pop |
| * - we gather the stuff that should not be killed into tree |
| * and stack is just a path from root to the current pointer. |
| * |
| * Future optimizations: |
| * |
| * - don't just push entire root set; process in place |
| * |
| * Fixes: |
| * Alan Cox 07 Sept 1997 Vmalloc internal stack as needed. |
| * Cope with changing max_files. |
| * Al Viro 11 Oct 1998 |
| * Graph may have cycles. That is, we can send the descriptor |
| * of foo to bar and vice versa. Current code chokes on that. |
| * Fix: move SCM_RIGHTS ones into the separate list and then |
| * skb_free() them all instead of doing explicit fput's. |
| * Another problem: since fput() may block somebody may |
| * create a new unix_socket when we are in the middle of sweep |
| * phase. Fix: revert the logic wrt MARKED. Mark everything |
| * upon the beginning and unmark non-junk ones. |
| * |
| * [12 Oct 1998] AAARGH! New code purges all SCM_RIGHTS |
| * sent to connect()'ed but still not accept()'ed sockets. |
| * Fixed. Old code had slightly different problem here: |
| * extra fput() in situation when we passed the descriptor via |
| * such socket and closed it (descriptor). That would happen on |
| * each unix_gc() until the accept(). Since the struct file in |
| * question would go to the free list and might be reused... |
| * That might be the reason of random oopses on filp_close() |
| * in unrelated processes. |
| * |
| * AV 28 Feb 1999 |
| * Kill the explicit allocation of stack. Now we keep the tree |
| * with root in dummy + pointer (gc_current) to one of the nodes. |
| * Stack is represented as path from gc_current to dummy. Unmark |
| * now means "add to tree". Push == "make it a son of gc_current". |
| * Pop == "move gc_current to parent". We keep only pointers to |
| * parents (->gc_tree). |
| * AV 1 Mar 1999 |
| * Damn. Added missing check for ->dead in listen queues scanning. |
| * |
| * Miklos Szeredi 25 Jun 2007 |
| * Reimplement with a cycle collecting algorithm. This should |
| * solve several problems with the previous code, like being racy |
| * wrt receive and holding up unrelated socket operations. |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/string.h> |
| #include <linux/socket.h> |
| #include <linux/un.h> |
| #include <linux/net.h> |
| #include <linux/fs.h> |
| #include <linux/skbuff.h> |
| #include <linux/netdevice.h> |
| #include <linux/file.h> |
| #include <linux/proc_fs.h> |
| #include <linux/mutex.h> |
| #include <linux/wait.h> |
| |
| #include <net/sock.h> |
| #include <net/af_unix.h> |
| #include <net/scm.h> |
| #include <net/tcp_states.h> |
| |
| #include "scm.h" |
| |
| /* Internal data structures and random procedures: */ |
| |
| static LIST_HEAD(gc_candidates); |
| static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait); |
| |
| static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *), |
| struct sk_buff_head *hitlist) |
| { |
| struct sk_buff *skb; |
| struct sk_buff *next; |
| |
| spin_lock(&x->sk_receive_queue.lock); |
| skb_queue_walk_safe(&x->sk_receive_queue, skb, next) { |
| /* Do we have file descriptors ? */ |
| if (UNIXCB(skb).fp) { |
| bool hit = false; |
| /* Process the descriptors of this socket */ |
| int nfd = UNIXCB(skb).fp->count; |
| struct file **fp = UNIXCB(skb).fp->fp; |
| |
| while (nfd--) { |
| /* Get the socket the fd matches if it indeed does so */ |
| struct sock *sk = unix_get_socket(*fp++); |
| |
| if (sk) { |
| struct unix_sock *u = unix_sk(sk); |
| |
| /* Ignore non-candidates, they could |
| * have been added to the queues after |
| * starting the garbage collection |
| */ |
| if (test_bit(UNIX_GC_CANDIDATE, &u->gc_flags)) { |
| hit = true; |
| |
| func(u); |
| } |
| } |
| } |
| if (hit && hitlist != NULL) { |
| __skb_unlink(skb, &x->sk_receive_queue); |
| __skb_queue_tail(hitlist, skb); |
| } |
| } |
| } |
| spin_unlock(&x->sk_receive_queue.lock); |
| } |
| |
| static void scan_children(struct sock *x, void (*func)(struct unix_sock *), |
| struct sk_buff_head *hitlist) |
| { |
| if (x->sk_state != TCP_LISTEN) { |
| scan_inflight(x, func, hitlist); |
| } else { |
| struct sk_buff *skb; |
| struct sk_buff *next; |
| struct unix_sock *u; |
| LIST_HEAD(embryos); |
| |
| /* For a listening socket collect the queued embryos |
| * and perform a scan on them as well. |
| */ |
| spin_lock(&x->sk_receive_queue.lock); |
| skb_queue_walk_safe(&x->sk_receive_queue, skb, next) { |
| u = unix_sk(skb->sk); |
| |
| /* An embryo cannot be in-flight, so it's safe |
| * to use the list link. |
| */ |
| BUG_ON(!list_empty(&u->link)); |
| list_add_tail(&u->link, &embryos); |
| } |
| spin_unlock(&x->sk_receive_queue.lock); |
| |
| while (!list_empty(&embryos)) { |
| u = list_entry(embryos.next, struct unix_sock, link); |
| scan_inflight(&u->sk, func, hitlist); |
| list_del_init(&u->link); |
| } |
| } |
| } |
| |
| static void dec_inflight(struct unix_sock *usk) |
| { |
| usk->inflight--; |
| } |
| |
| static void inc_inflight(struct unix_sock *usk) |
| { |
| usk->inflight++; |
| } |
| |
| static void inc_inflight_move_tail(struct unix_sock *u) |
| { |
| u->inflight++; |
| |
| /* If this still might be part of a cycle, move it to the end |
| * of the list, so that it's checked even if it was already |
| * passed over |
| */ |
| if (test_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags)) |
| list_move_tail(&u->link, &gc_candidates); |
| } |
| |
| static bool gc_in_progress; |
| #define UNIX_INFLIGHT_TRIGGER_GC 16000 |
| |
| void wait_for_unix_gc(void) |
| { |
| /* If number of inflight sockets is insane, |
| * force a garbage collect right now. |
| * Paired with the WRITE_ONCE() in unix_inflight(), |
| * unix_notinflight() and gc_in_progress(). |
| */ |
| if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC && |
| !READ_ONCE(gc_in_progress)) |
| unix_gc(); |
| wait_event(unix_gc_wait, gc_in_progress == false); |
| } |
| |
| /* The external entry point: unix_gc() */ |
| void unix_gc(void) |
| { |
| struct sk_buff *next_skb, *skb; |
| struct unix_sock *u; |
| struct unix_sock *next; |
| struct sk_buff_head hitlist; |
| struct list_head cursor; |
| LIST_HEAD(not_cycle_list); |
| |
| spin_lock(&unix_gc_lock); |
| |
| /* Avoid a recursive GC. */ |
| if (gc_in_progress) |
| goto out; |
| |
| /* Paired with READ_ONCE() in wait_for_unix_gc(). */ |
| WRITE_ONCE(gc_in_progress, true); |
| |
| /* First, select candidates for garbage collection. Only |
| * in-flight sockets are considered, and from those only ones |
| * which don't have any external reference. |
| * |
| * Holding unix_gc_lock will protect these candidates from |
| * being detached, and hence from gaining an external |
| * reference. Since there are no possible receivers, all |
| * buffers currently on the candidates' queues stay there |
| * during the garbage collection. |
| * |
| * We also know that no new candidate can be added onto the |
| * receive queues. Other, non candidate sockets _can_ be |
| * added to queue, so we must make sure only to touch |
| * candidates. |
| * |
| * Embryos, though never candidates themselves, affect which |
| * candidates are reachable by the garbage collector. Before |
| * being added to a listener's queue, an embryo may already |
| * receive data carrying SCM_RIGHTS, potentially making the |
| * passed socket a candidate that is not yet reachable by the |
| * collector. It becomes reachable once the embryo is |
| * enqueued. Therefore, we must ensure that no SCM-laden |
| * embryo appears in a (candidate) listener's queue between |
| * consecutive scan_children() calls. |
| */ |
| list_for_each_entry_safe(u, next, &gc_inflight_list, link) { |
| struct sock *sk = &u->sk; |
| long total_refs; |
| |
| total_refs = file_count(sk->sk_socket->file); |
| |
| BUG_ON(!u->inflight); |
| BUG_ON(total_refs < u->inflight); |
| if (total_refs == u->inflight) { |
| list_move_tail(&u->link, &gc_candidates); |
| __set_bit(UNIX_GC_CANDIDATE, &u->gc_flags); |
| __set_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); |
| |
| if (sk->sk_state == TCP_LISTEN) { |
| unix_state_lock(sk); |
| unix_state_unlock(sk); |
| } |
| } |
| } |
| |
| /* Now remove all internal in-flight reference to children of |
| * the candidates. |
| */ |
| list_for_each_entry(u, &gc_candidates, link) |
| scan_children(&u->sk, dec_inflight, NULL); |
| |
| /* Restore the references for children of all candidates, |
| * which have remaining references. Do this recursively, so |
| * only those remain, which form cyclic references. |
| * |
| * Use a "cursor" link, to make the list traversal safe, even |
| * though elements might be moved about. |
| */ |
| list_add(&cursor, &gc_candidates); |
| while (cursor.next != &gc_candidates) { |
| u = list_entry(cursor.next, struct unix_sock, link); |
| |
| /* Move cursor to after the current position. */ |
| list_move(&cursor, &u->link); |
| |
| if (u->inflight) { |
| list_move_tail(&u->link, ¬_cycle_list); |
| __clear_bit(UNIX_GC_MAYBE_CYCLE, &u->gc_flags); |
| scan_children(&u->sk, inc_inflight_move_tail, NULL); |
| } |
| } |
| list_del(&cursor); |
| |
| /* Now gc_candidates contains only garbage. Restore original |
| * inflight counters for these as well, and remove the skbuffs |
| * which are creating the cycle(s). |
| */ |
| skb_queue_head_init(&hitlist); |
| list_for_each_entry(u, &gc_candidates, link) |
| scan_children(&u->sk, inc_inflight, &hitlist); |
| |
| /* not_cycle_list contains those sockets which do not make up a |
| * cycle. Restore these to the inflight list. |
| */ |
| while (!list_empty(¬_cycle_list)) { |
| u = list_entry(not_cycle_list.next, struct unix_sock, link); |
| __clear_bit(UNIX_GC_CANDIDATE, &u->gc_flags); |
| list_move_tail(&u->link, &gc_inflight_list); |
| } |
| |
| spin_unlock(&unix_gc_lock); |
| |
| /* We need io_uring to clean its registered files, ignore all io_uring |
| * originated skbs. It's fine as io_uring doesn't keep references to |
| * other io_uring instances and so killing all other files in the cycle |
| * will put all io_uring references forcing it to go through normal |
| * release.path eventually putting registered files. |
| */ |
| skb_queue_walk_safe(&hitlist, skb, next_skb) { |
| if (skb->scm_io_uring) { |
| __skb_unlink(skb, &hitlist); |
| skb_queue_tail(&skb->sk->sk_receive_queue, skb); |
| } |
| } |
| |
| /* Here we are. Hitlist is filled. Die. */ |
| __skb_queue_purge(&hitlist); |
| |
| spin_lock(&unix_gc_lock); |
| |
| /* There could be io_uring registered files, just push them back to |
| * the inflight list |
| */ |
| list_for_each_entry_safe(u, next, &gc_candidates, link) |
| list_move_tail(&u->link, &gc_inflight_list); |
| |
| /* All candidates should have been detached by now. */ |
| BUG_ON(!list_empty(&gc_candidates)); |
| |
| /* Paired with READ_ONCE() in wait_for_unix_gc(). */ |
| WRITE_ONCE(gc_in_progress, false); |
| |
| wake_up(&unix_gc_wait); |
| |
| out: |
| spin_unlock(&unix_gc_lock); |
| } |