[PATCH 3.12 052/113] tcp: fix 0 divide in __tcp_select_window()

From: Jiri Slaby
Date: Mon Mar 06 2017 - 04:32:04 EST


From: Eric Dumazet <edumazet@xxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

[ Upstream commit 06425c308b92eaf60767bc71d359f4cbc7a561f8 ]

syszkaller fuzzer was able to trigger a divide by zero, when
TCP window scaling is not enabled.

SO_RCVBUF can be used not only to increase sk_rcvbuf, also
to decrease it below current receive buffers utilization.

If mss is negative or 0, just return a zero TCP window.

Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
net/ipv4/tcp_output.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c807d5790ca1..d92c4b69f7ea 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2163,9 +2163,11 @@ u32 __tcp_select_window(struct sock *sk)
int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
int window;

- if (mss > full_space)
+ if (unlikely(mss > full_space)) {
mss = full_space;
-
+ if (mss <= 0)
+ return 0;
+ }
if (free_space < (full_space >> 1)) {
icsk->icsk_ack.quick = 0;

--
2.12.0