/* * 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. * */ #include <linux/kernel.h> #include <linux/sched.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 <net/sock.h> #include <net/af_unix.h> #include <net/scm.h> #include <net/tcp_states.h> /* Internal data structures and random procedures: */ #define GC_HEAD ((struct sock *)(-1)) #define GC_ORPHAN ((struct sock *)(-3)) static struct sock *gc_current = GC_HEAD; /* stack of objects to mark */ atomic_t unix_tot_inflight = ATOMIC_INIT(0); static struct sock *unix_get_socket(struct file *filp) { struct sock *u_sock = NULL; struct inode *inode = filp->f_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) { atomic_inc(&unix_sk(s)->inflight); atomic_inc(&unix_tot_inflight); } } void unix_notinflight(struct file *fp) { struct sock *s = unix_get_socket(fp); if(s) { atomic_dec(&unix_sk(s)->inflight); atomic_dec(&unix_tot_inflight); } } /* * Garbage Collector Support Functions */ static inline struct sock *pop_stack(void) { struct sock *p = gc_current; gc_current = unix_sk(p)->gc_tree; return p; } static inline int empty_stack(void) { return gc_current == GC_HEAD; } static void maybe_unmark_and_push(struct sock *x) { struct unix_sock *u = unix_sk(x); if (u->gc_tree != GC_ORPHAN) return; sock_hold(x); u->gc_tree = gc_current; gc_current = x; } /* The external entry point: unix_gc() */ void unix_gc(void) { static DECLARE_MUTEX(unix_gc_sem); int i; struct sock *s; struct sk_buff_head hitlist; struct sk_buff *skb; /* * Avoid a recursive GC. */ if (down_trylock(&unix_gc_sem)) return; read_lock(&unix_table_lock); forall_unix_sockets(i, s) { unix_sk(s)->gc_tree = GC_ORPHAN; } /* * Everything is now marked */ /* Invariant to be maintained: - everything unmarked is either: -- (a) on the stack, or -- (b) has all of its children unmarked - everything on the stack is always unmarked - nothing is ever pushed onto the stack twice, because: -- nothing previously unmarked is ever pushed on the stack */ /* * Push root set */ forall_unix_sockets(i, s) { int open_count = 0; /* * If all instances of the descriptor are not * in flight we are in use. * * Special case: when socket s is embrion, it may be * hashed but still not in queue of listening socket. * In this case (see unix_create1()) we set artificial * negative inflight counter to close race window. * It is trick of course and dirty one. */ if (s->sk_socket && s->sk_socket->file) open_count = file_count(s->sk_socket->file); if (open_count > atomic_read(&unix_sk(s)->inflight)) maybe_unmark_and_push(s); } /* * Mark phase */ while (!empty_stack()) { struct sock *x = pop_stack(); struct sock *sk; spin_lock(&x->sk_receive_queue.lock); skb = skb_peek(&x->sk_receive_queue); /* * Loop through all but first born */ while (skb && skb != (struct sk_buff *)&x->sk_receive_queue) { /* * Do we have file descriptors ? */ if(UNIXCB(skb).fp) { /* * 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 */ if((sk=unix_get_socket(*fp++))!=NULL) { maybe_unmark_and_push(sk); } } } /* We have to scan not-yet-accepted ones too */ if (x->sk_state == TCP_LISTEN) maybe_unmark_and_push(skb->sk); skb=skb->next; } spin_unlock(&x->sk_receive_queue.lock); sock_put(x); } skb_queue_head_init(&hitlist); forall_unix_sockets(i, s) { struct unix_sock *u = unix_sk(s); if (u->gc_tree == GC_ORPHAN) { struct sk_buff *nextsk; spin_lock(&s->sk_receive_queue.lock); skb = skb_peek(&s->sk_receive_queue); while (skb && skb != (struct sk_buff *)&s->sk_receive_queue) { nextsk = skb->next; /* * Do we have file descriptors ? */ if (UNIXCB(skb).fp) { __skb_unlink(skb, &s->sk_receive_queue); __skb_queue_tail(&hitlist, skb); } skb = nextsk; } spin_unlock(&s->sk_receive_queue.lock); } u->gc_tree = GC_ORPHAN; } read_unlock(&unix_table_lock); /* * Here we are. Hitlist is filled. Die. */ __skb_queue_purge(&hitlist); up(&unix_gc_sem); }