Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753833Ab2KGAQ2 (ORCPT ); Tue, 6 Nov 2012 19:16:28 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:58569 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753314Ab2KGAQ1 (ORCPT ); Tue, 6 Nov 2012 19:16:27 -0500 From: Julius Werner To: linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org, Patrick McHardy , Hideaki YOSHIFUJI , James Morris , Alexey Kuznetsov , "David S. Miller" , Sameer Nanda , Mandeep Singh Baines , Eric Dumazet , Julius Werner Subject: [PATCH] tcp: Replace infinite loop on recvmsg bug with proper crash Date: Tue, 6 Nov 2012 16:15:35 -0800 Message-Id: <1352247335-10396-1-git-send-email-jwerner@chromium.org> X-Mailer: git-send-email 1.7.7.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1811 Lines: 44 tcp_recvmsg contains a sanity check that WARNs when there is a gap between the socket's copied_seq and the first buffer in the sk_receive_queue. In theory, the TCP stack makes sure that This Should Never Happen (TM)... however, practice shows that there are still a few bug reports from it out there (and one in my inbox). Unfortunately, when it does happen for whatever reason, the situation is not handled very well: the kernel logs a warning and breaks out of the loop that walks the receive queue. It proceeds to find nothing else to do on the socket and hits sk_wait_data, which cannot block because the receive queue is not empty. As no data was read, the outer while loop repeats (logging the same warning again) ad infinitum until the system's syslog exhausts all available hard drive capacity. This patch improves that behavior by going straight to a proper kernel crash. The cause of the error can be identified right away and the system's hard drive is not unnecessarily strained. Signed-off-by: Julius Werner --- net/ipv4/tcp.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 197c000..fcb0927 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1628,7 +1628,7 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, "recvmsg bug: copied %X seq %X rcvnxt %X fl %X\n", *seq, TCP_SKB_CB(skb)->seq, tp->rcv_nxt, flags)) - break; + BUG(); offset = *seq - TCP_SKB_CB(skb)->seq; if (tcp_hdr(skb)->syn) -- 1.7.8.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/