| From stable-bounces@linux.kernel.org Thu Oct 19 18:53:27 2006 |
| From: NeilBrown <neilb@suse.de> |
| To: Andrew Morton <akpm@osdl.org> |
| Date: Fri, 20 Oct 2006 11:52:44 +1000 |
| Message-Id: <1061020015244.26756@suse.de> |
| Cc: Adrian Bunk <bunk@stusta.de>, nfs@lists.sourceforge.net, linux-kernel@vger.kernel.org, stable@kernel.org |
| Subject: knfsd: Fix race that can disable NFS server. |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset="us-ascii" |
| |
| From: NeilBrown <neilb@suse.de> |
| |
| This is a long standing bug that seems to have only recently become |
| apparent, presumably due to increasing use of NFS over TCP - many |
| distros seem to be making it the default. |
| |
| The SK_CONN bit gets set when a listening socket may be ready |
| for an accept, just as SK_DATA is set when data may be available. |
| |
| It is entirely possible for svc_tcp_accept to be called with neither |
| of these set. It doesn't happen often but there is a small race in |
| svc_sock_enqueue as SK_CONN and SK_DATA are tested outside the |
| spin_lock. They could be cleared immediately after the test and |
| before the lock is gained. |
| |
| This normally shouldn't be a problem. The sockets are non-blocking so |
| trying to read() or accept() when ther is nothing to do is not a problem. |
| |
| However: svc_tcp_recvfrom makes the decision "Should I accept() or |
| should I read()" based on whether SK_CONN is set or not. This usually |
| works but is not safe. The decision should be based on whether it is |
| a TCP_LISTEN socket or a TCP_CONNECTED socket. |
| |
| |
| Signed-off-by: Neil Brown <neilb@suse.de> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| Signed-off-by: Chris Wright <chrisw@sous-sol.org> |
| |
| --- |
| net/sunrpc/svcsock.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- linux-2.6.18.1.orig/net/sunrpc/svcsock.c |
| +++ linux-2.6.18.1/net/sunrpc/svcsock.c |
| @@ -902,7 +902,7 @@ svc_tcp_recvfrom(struct svc_rqst *rqstp) |
| return 0; |
| } |
| |
| - if (test_bit(SK_CONN, &svsk->sk_flags)) { |
| + if (svsk->sk_sk->sk_state == TCP_LISTEN) { |
| svc_tcp_accept(svsk); |
| svc_sock_received(svsk); |
| return 0; |
