Commit aaf68cfb authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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[PATCH] knfsd: fix a race in closing NFSd connections 

If you lose this race, it can iput a socket inode twice and you get a BUG
in fs/inode.c

When I added the option for user-space to close a socket, I added some
cruft to svc_delete_socket so that I could call that function when closing
a socket per user-space request.

This was the wrong thing to do.  I should have just set SK_CLOSE and let
normal mechanisms do the work.

Not only wrong, but buggy.  The locking is all wrong and it openned up a
race where-by a socket could be closed twice.

So this patch:
  Introduces svc_close_socket which sets SK_CLOSE then either leave
  the close up to a thread, or calls svc_delete_socket if it can
  get SK_BUSY.

  Adds a bias to sk_busy which is removed when SK_DEAD is set,
  This avoid races around shutting down the socket.

  Changes several 'spin_lock' to 'spin_lock_bh' where the _bh
  was missing.

Bugzilla-url: http://bugzilla.kernel.org/show_bug.cgi?id=7916



Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 387bb173

include/linux/sunrpc/svcsock.h

+1 −1
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ struct svc_sock { 
 * Function prototypes.

 */

int		svc_makesock(struct svc_serv *, int, unsigned short);

void		svc_delete_socket(struct svc_sock *);

void		svc_close_socket(struct svc_sock *);

int		svc_recv(struct svc_rqst *, long);

int		svc_send(struct svc_rqst *);

void		svc_drop(struct svc_rqst *);

net/sunrpc/svc.c

+2 −2
Original line number Diff line number Diff line
@@ -386,7 +386,7 @@ svc_destroy(struct svc_serv *serv) 
		svsk = list_entry(serv->sv_tempsocks.next,

				  struct svc_sock,

				  sk_list);

		svc_delete_socket(svsk);

		svc_close_socket(svsk);

	}

	if (serv->sv_shutdown)

		serv->sv_shutdown(serv);
@@ -395,7 +395,7 @@ svc_destroy(struct svc_serv *serv) 
		svsk = list_entry(serv->sv_permsocks.next,

				  struct svc_sock,

				  sk_list);

		svc_delete_socket(svsk);

		svc_close_socket(svsk);

	}

	

	cache_clean_deferred(serv);

net/sunrpc/svcsock.c

+38 −14
Original line number Diff line number Diff line
@@ -62,6 +62,12 @@ 
 *		after a clear, the socket must be read/accepted

 *		 if this succeeds, it must be set again.

 *	SK_CLOSE can set at any time. It is never cleared.

 *      sk_inuse contains a bias of '1' until SK_DEAD is set.

 *             so when sk_inuse hits zero, we know the socket is dead

 *             and no-one is using it.

 *      SK_DEAD can only be set while SK_BUSY is held which ensures

 *             no other thread will be using the socket or will try to

 *	       set SK_DEAD.

 *

 */
@@ -70,6 +76,7 @@ 


static struct svc_sock *svc_setup_socket(struct svc_serv *, struct socket *,

					 int *errp, int pmap_reg);

static void		svc_delete_socket(struct svc_sock *svsk);

static void		svc_udp_data_ready(struct sock *, int);

static int		svc_udp_recvfrom(struct svc_rqst *);

static int		svc_udp_sendto(struct svc_rqst *);
@@ -329,8 +336,9 @@ void svc_reserve(struct svc_rqst *rqstp, int space) 
static inline void

svc_sock_put(struct svc_sock *svsk)

{

	if (atomic_dec_and_test(&svsk->sk_inuse) &&

			test_bit(SK_DEAD, &svsk->sk_flags)) {

	if (atomic_dec_and_test(&svsk->sk_inuse)) {

		BUG_ON(! test_bit(SK_DEAD, &svsk->sk_flags));



		dprintk("svc: releasing dead socket\n");

		if (svsk->sk_sock->file)

			sockfd_put(svsk->sk_sock);
@@ -520,7 +528,7 @@ svc_sock_names(char *buf, struct svc_serv *serv, char *toclose) 


	if (!serv)

		return 0;

	spin_lock(&serv->sv_lock);

	spin_lock_bh(&serv->sv_lock);

	list_for_each_entry(svsk, &serv->sv_permsocks, sk_list) {

		int onelen = one_sock_name(buf+len, svsk);

		if (toclose && strcmp(toclose, buf+len) == 0)
@@ -528,12 +536,12 @@ svc_sock_names(char *buf, struct svc_serv *serv, char *toclose) 
		else

			len += onelen;

	}

	spin_unlock(&serv->sv_lock);

	spin_unlock_bh(&serv->sv_lock);

	if (closesk)

		/* Should unregister with portmap, but you cannot

		 * unregister just one protocol...

		 */

		svc_delete_socket(closesk);

		svc_close_socket(closesk);

	else if (toclose)

		return -ENOENT;

	return len;
@@ -683,6 +691,11 @@ svc_udp_recvfrom(struct svc_rqst *rqstp) 
		return svc_deferred_recv(rqstp);

	}



	if (test_bit(SK_CLOSE, &svsk->sk_flags)) {

		svc_delete_socket(svsk);

		return 0;

	}



	clear_bit(SK_DATA, &svsk->sk_flags);

	while ((skb = skb_recv_datagram(svsk->sk_sk, 0, 1, &err)) == NULL) {

		if (err == -EAGAIN) {
@@ -1176,7 +1189,8 @@ svc_tcp_sendto(struct svc_rqst *rqstp) 
		       rqstp->rq_sock->sk_server->sv_name,

		       (sent<0)?"got error":"sent only",

		       sent, xbufp->len);

		svc_delete_socket(rqstp->rq_sock);

		set_bit(SK_CLOSE, &rqstp->rq_sock->sk_flags);

		svc_sock_enqueue(rqstp->rq_sock);

		sent = -EAGAIN;

	}

	return sent;
@@ -1495,7 +1509,7 @@ svc_setup_socket(struct svc_serv *serv, struct socket *sock, 
	svsk->sk_odata = inet->sk_data_ready;

	svsk->sk_owspace = inet->sk_write_space;

	svsk->sk_server = serv;

	atomic_set(&svsk->sk_inuse, 0);

	atomic_set(&svsk->sk_inuse, 1);

	svsk->sk_lastrecv = get_seconds();

	spin_lock_init(&svsk->sk_defer_lock);

	INIT_LIST_HEAD(&svsk->sk_deferred);
@@ -1618,7 +1632,7 @@ bummer: 
/*

 * Remove a dead socket

 */

void

static void

svc_delete_socket(struct svc_sock *svsk)

{

	struct svc_serv	*serv;
@@ -1644,16 +1658,26 @@ svc_delete_socket(struct svc_sock *svsk) 
	 * while still attached to a queue, the queue itself

	 * is about to be destroyed (in svc_destroy).

	 */

	if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags))

	if (!test_and_set_bit(SK_DEAD, &svsk->sk_flags)) {

		BUG_ON(atomic_read(&svsk->sk_inuse)<2);

		atomic_dec(&svsk->sk_inuse);

		if (test_bit(SK_TEMP, &svsk->sk_flags))

			serv->sv_tmpcnt--;

	}



	/* This atomic_inc should be needed - svc_delete_socket

	 * should have the semantic of dropping a reference.

	 * But it doesn't yet....

	 */

	atomic_inc(&svsk->sk_inuse);

	spin_unlock_bh(&serv->sv_lock);

}



void svc_close_socket(struct svc_sock *svsk)

{

	set_bit(SK_CLOSE, &svsk->sk_flags);

	if (test_and_set_bit(SK_BUSY, &svsk->sk_flags))

		/* someone else will have to effect the close */

		return;



	atomic_inc(&svsk->sk_inuse);

	svc_delete_socket(svsk);

	clear_bit(SK_BUSY, &svsk->sk_flags);

	svc_sock_put(svsk);

}

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