diff mbox

[net] tcp: fix 0 divide in __tcp_select_window()

Message ID 1485966833.6360.149.camel@edumazet-glaptop3.roam.corp.google.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Feb. 1, 2017, 4:33 p.m. UTC 
From: Eric Dumazet <edumazet@google.com>

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@google.com>
Reported-by: Dmitry Vyukov  <dvyukov@google.com>
---
No Fixes: tag, this is a day-0 bug.

 net/ipv4/tcp_output.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Neal Cardwell Feb. 1, 2017, 4:41 p.m. UTC | #1 
On Wed, Feb 1, 2017 at 11:33 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
>
> From: Eric Dumazet <edumazet@google.com>
>
> 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@google.com>
> Reported-by: Dmitry Vyukov  <dvyukov@google.com>
> ---

Acked-by: Neal Cardwell <ncardwell@google.com>

Thanks, Eric!

neal
David Miller Feb. 1, 2017, 5:56 p.m. UTC | #2 
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Wed, 01 Feb 2017 08:33:53 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> 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@google.com>
> Reported-by: Dmitry Vyukov  <dvyukov@google.com>
> ---
> No Fixes: tag, this is a day-0 bug.

Applied and queued up for -stable, thanks Eric.
diff mbox

Patch

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 1d5331a1b1dc2677316148ba9852c191e7ed0fd4..8ce50dc3ab8cac821b8a2c3e0d31f0aa42f5c9d5 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2518,9 +2518,11 @@  u32 __tcp_select_window(struct sock *sk)
 	int full_space = min_t(int, tp->window_clamp, allowed_space);
 	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;