[Devel] [PATCH RHEL7 COMMIT] ms/tcp: avoid infinite loop in tcp_splice_read()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.6.1.vz7.28.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.6.1.vz7.28.7
------>
commit b207397b05680d0d47b484ff3090194eb10f5cc8
Author: Eric Dumazet <edumazet at google.com>
Date:   Fri Feb 3 14:59:38 2017 -0800

    ms/tcp: avoid infinite loop in tcp_splice_read()
    
    Splicing from TCP socket is vulnerable when a packet with URG flag is
    received and stored into receive queue.
    
    __tcp_splice_read() returns 0, and sk_wait_data() immediately
    returns since there is the problematic skb in queue.
    
    This is a nice way to burn cpu (aka infinite loop) and trigger
    soft lockups.
    
    Again, this gem was found by syzkaller tool.
    
    Fixes: 9c55e01c0cc8 ("[TCP]: Splice receive support.")
    Signed-off-by: Eric Dumazet <edumazet at google.com>
    Reported-by: Dmitry Vyukov  <dvyukov at google.com>
    Cc: Willy Tarreau <w at 1wt.eu>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    
    https://jira.sw.ru/browse/PSBM-61135
    https://bugzilla.redhat.com/show_bug.cgi?id=1426542
    CVE-2017-6214 kernel: ipv4/tcp: Infinite loop in tcp_splice_read()
    
    (cherry picked from commit ccf7abb93af09ad0868ae9033d1ca8108bdaec82)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 net/ipv4/tcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 277e3d2..1f7df79 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -768,6 +768,12 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 				ret = -EAGAIN;
 				break;
 			}
+			/* if __tcp_splice_read() got nothing while we have
+			 * an skb in receive queue, we do not want to loop.
+			 * This might happen with URG data.
+			 */
+			if (!skb_queue_empty(&sk->sk_receive_queue))
+				break;
 			sk_wait_data(sk, &timeo, NULL);
 			if (signal_pending(current)) {
 				ret = sock_intr_errno(timeo);