Patch "tcp: fix 0 divide in __tcp_select_window()" has been added to the 4.9-stable tree

Patch "tcp: fix 0 divide in __tcp_select_window()" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tcp: fix 0 divide in __tcp_select_window()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-fix-0-divide-in-__tcp_select_window.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Feb 14 17:03:08 PST 2017
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 1 Feb 2017 08:33:53 -0800
Subject: tcp: fix 0 divide in __tcp_select_window()

From: Eric Dumazet <edumazet@google.com>


[ 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@google.com>
Reported-by: Dmitry Vyukov  <dvyukov@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_output.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2436,9 +2436,11 @@ 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;
 


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.9/ipv6-pointer-math-error-in-ip6_tnl_parse_tlv_enc_lim.patch
queue-4.9/netlabel-out-of-bound-access-in-cipso_v4_validate.patch
queue-4.9/packet-round-up-linear-to-header-len.patch
queue-4.9/tun-read-vnet_hdr_sz-once.patch
queue-4.9/ipv6-fix-ip6_tnl_parse_tlv_enc_lim.patch
queue-4.9/l2tp-do-not-use-udp_ioctl.patch
queue-4.9/tcp-fix-0-divide-in-__tcp_select_window.patch
queue-4.9/can-fix-kernel-panic-at-security_sock_rcv_skb.patch
queue-4.9/net-introduce-device-min_header_len.patch
queue-4.9/macvtap-read-vnet_hdr_size-once.patch
queue-4.9/tcp-avoid-infinite-loop-in-tcp_splice_read.patch
queue-4.9/mlx4-invoke-softirqs-after-napi_reschedule.patch
queue-4.9/ipv6-tcp-add-a-missing-tcp_v6_restore_cb.patch
queue-4.9/ipv4-keep-skb-dst-around-in-presence-of-ip-options.patch
queue-4.9/net-use-a-work-queue-to-defer-net_disable_timestamp-work.patch
queue-4.9/ip6_gre-fix-ip6gre_err-invalid-reads.patch