/*
* 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);
}
