/* * NET3: Garbage Collector For AF_UNIX sockets * * Garbage Collector: * Copyright (C) Barak A. Pearlmutter. * Released under the GPL version 2 or later. * * 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 * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. * * 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/slab.h> #include <linux/skbuff.h> #include <linux/netdevice.h> #include <linux/file.h> #include <linux/proc_fs.h> #include <linux/mutex.h> #include <net/sock.h> #include <net/af_unix.h> #include <net/scm.h> #include <net/tcp_states.h> /* Internal data structures and random procedures: */ static LIST_HEAD(gc_inflight_list); static LIST_HEAD(gc_candidates); static DEFINE_SPINLOCK(unix_gc_lock); unsigned int unix_tot_inflight; static struct sock *unix_get_socket(struct file *filp) { struct sock *u_sock = NULL; struct inode *inode = filp->f_path.dentry->d_inode; /* * Socket ? */ if (S_ISSOCK(inode->i_mode)) { struct socket * sock = SOCKET_I(inode); struct sock * s = sock->sk; /* * PF_UNIX ? */ if (s && sock->ops && sock->ops->family == PF_UNIX) u_sock = s; } return u_sock; } /* * Keep the number of times in flight count for the file * descriptor if it is for an AF_UNIX socket. */ void unix_inflight(struct file *fp) { struct sock *s = unix_get_socket(fp); if(s) { struct unix_sock *u = unix_sk(s); spin_lock(&unix_gc_lock); if (atomic_inc_return(&u->inflight) == 1) { BUG_ON(!list_empty(&u->link)); list_add_tail(&u->link, &gc_inflight_list); } else { BUG_ON(list_empty(&u->link)); } unix_tot_inflight++; spin_unlock(&unix_gc_lock); } } void unix_notinflight(struct file *fp) { struct sock *s = unix_get_socket(fp); if(s) { struct unix_sock *u = unix_sk(s); spin_lock(&unix_gc_lock); BUG_ON(list_empty(&u->link)); if (atomic_dec_and_test(&u->inflight)) list_del_init(&u->link); unix_tot_inflight--; spin_unlock(&unix_gc_lock); } } static inline struct sk_buff *sock_queue_head(struct sock *sk) { return (struct sk_buff *) &sk->sk_receive_queue; } #define receive_queue_for_each_skb(sk, next, skb) \ for (skb = sock_queue_head(sk)->next, next = skb->next; \ skb != sock_queue_head(sk); skb = next, next = skb->next) 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); receive_queue_for_each_skb(x, next, skb) { /* * 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) { hit = true; func(unix_sk(sk)); } } 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); receive_queue_for_each_skb(x, next, skb) { 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) { atomic_dec(&usk->inflight); } static void inc_inflight(struct unix_sock *usk) { atomic_inc(&usk->inflight); } static void inc_inflight_move_tail(struct unix_sock *u) { atomic_inc(&u->inflight); /* * If this is still a candidate, move it to the end of the * list, so that it's checked even if it was already passed * over */ if (u->gc_candidate) list_move_tail(&u->link, &gc_candidates); } /* The external entry point: unix_gc() */ void unix_gc(void) { static bool gc_in_progress = false; struct unix_sock *u; struct unix_sock *next; struct sk_buff_head hitlist; struct list_head cursor; spin_lock(&unix_gc_lock); /* Avoid a recursive GC. */ if (gc_in_progress) goto out; 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. This also means, that since there are no * possible receivers, the receive queues of these sockets are * static during the GC, even though the dequeue is done * before the detach without atomicity guarantees. */ list_for_each_entry_safe(u, next, &gc_inflight_list, link) { int total_refs; int inflight_refs; total_refs = file_count(u->sk.sk_socket->file); inflight_refs = atomic_read(&u->inflight); BUG_ON(inflight_refs < 1); BUG_ON(total_refs < inflight_refs); if (total_refs == inflight_refs) { list_move_tail(&u->link, &gc_candidates); u->gc_candidate = 1; } } /* * 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 (atomic_read(&u->inflight) > 0) { list_move_tail(&u->link, &gc_inflight_list); u->gc_candidate = 0; 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); spin_unlock(&unix_gc_lock); /* Here we are. Hitlist is filled. Die. */ __skb_queue_purge(&hitlist); spin_lock(&unix_gc_lock); /* All candidates should have been detached by now. */ BUG_ON(!list_empty(&gc_candidates)); gc_in_progress = false; out: spin_unlock(&unix_gc_lock); }