From: NeilBrown Date: Fri, 20 Oct 2006 01:52:44 +0000 (+1000) Subject: [PATCH] knfsd: Fix race that can disable NFS server. X-Git-Tag: v2.6.18.2~33 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=02bb8f3f912d8a2048ed7502a733f64c6bf8fcfe;p=thirdparty%2Fkernel%2Fstable.git [PATCH] knfsd: Fix race that can disable NFS server. 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 Signed-off-by: Greg Kroah-Hartman Signed-off-by: Chris Wright --- diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index d9a95732df46a..2544acdbe119c 100644 --- a/net/sunrpc/svcsock.c +++ b/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;