tcp: fix crash in tcp_xmit_retransmit_queue

commit 45e77d314585869dfe43c82679f7e08c9b35b898 upstream.

It can happen that there are no packets in queue while calling
tcp_xmit_retransmit_queue(). tcp_write_queue_head() then returns
NULL and that gets deref'ed to get sacked into a local var.

There is no work to do if no packets are outstanding so we just
exit early.

This oops was introduced by 08ebd1721ab8fd (tcp: remove tp->lost_out
guard to make joining diff nicer).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Reported-by: Lennart Schulte <lennart.schulte@nets.rwth-aachen.de>
Tested-by: Lennart Schulte <lennart.schulte@nets.rwth-aachen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index fcd278a7080e1656060cd5f57e38764bec3bdb74..af83bdf559da50314c15c079147a4fab20257024 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2037,6 +2037,9 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
        int mib_idx;
        int fwd_rexmitting = 0;
 
+       if (!tp->packets_out)
+               return;
+
        if (!tp->lost_out)
                tp->retransmit_high = tp->snd_una;