[Astlinux-commits] SF.net SVN: astlinux:[7795] branches/1.0/project/astlinux/kernel-patches/ linux-800-tcp-make-challenge-acks-less-predictable.patch

[<abe...@us...>]

Revision: 7795
          http://sourceforge.net/p/astlinux/code/7795
Author:   abelbeck
Date:     2016-08-12 16:23:17 +0000 (Fri, 12 Aug 2016)
Log Message:
-----------
linux kernel, security fix: CVE-2016-5696 - Off-path TCP attack, make challenge acks less predictable
Ref: Ref: https://git.kernel.org/cgit/linux/kernel/git/bwh/linux-stable-queue.git/plain/queue-3.2/tcp-make-challenge-acks-less-predictable.patch?id=4da02c7fa853f92087e972f6b821bc7b7f7d4a99

Added Paths:
-----------
    branches/1.0/project/astlinux/kernel-patches/linux-800-tcp-make-challenge-acks-less-predictable.patch

Added: branches/1.0/project/astlinux/kernel-patches/linux-800-tcp-make-challenge-acks-less-predictable.patch
===================================================================
--- branches/1.0/project/astlinux/kernel-patches/linux-800-tcp-make-challenge-acks-less-predictable.patch	                        (rev 0)
+++ branches/1.0/project/astlinux/kernel-patches/linux-800-tcp-make-challenge-acks-less-predictable.patch	2016-08-12 16:23:17 UTC (rev 7795)
@@ -0,0 +1,76 @@
+From: Eric Dumazet <edu...@go...>
+Date: Sun, 10 Jul 2016 10:04:02 +0200
+Subject: tcp: make challenge acks less predictable
+
+commit 75ff39ccc1bd5d3c455b6822ab09e533c551f758 upstream.
+
+Yue Cao claims that current host rate limiting of challenge ACKS
+(RFC 5961) could leak enough information to allow a patient attacker
+to hijack TCP sessions. He will soon provide details in an academic
+paper.
+
+This patch increases the default limit from 100 to 1000, and adds
+some randomization so that the attacker can no longer hijack
+sessions without spending a considerable amount of probes.
+
+Based on initial analysis and patch from Linus.
+
+Note that we also have per socket rate limiting, so it is tempting
+to remove the host limit in the future.
+
+v2: randomize the count of challenge acks per second, not the period.
+
+Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2")
+Reported-by: Yue Cao <yc...@uc...>
+Signed-off-by: Eric Dumazet <edu...@go...>
+Suggested-by: Linus Torvalds <tor...@li...>
+Cc: Yuchung Cheng <yc...@go...>
+Cc: Neal Cardwell <nca...@go...>
+Acked-by: Neal Cardwell <nca...@go...>
+Acked-by: Yuchung Cheng <yc...@go...>
+Signed-off-by: David S. Miller <da...@da...>
+[bwh: Backported to 3.2:
+ - Adjust context
+ - Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()
+ - Open-code prandom_u32_max()]
+Signed-off-by: Ben Hutchings <be...@de...>
+---
+ net/ipv4/tcp_input.c | 17 ++++++++++++-----
+ 1 file changed, 12 insertions(+), 5 deletions(-)
+
+--- a/net/ipv4/tcp_input.c
++++ b/net/ipv4/tcp_input.c
+@@ -87,7 +87,7 @@ int sysctl_tcp_adv_win_scale __read_most
+ EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
+ 
+ /* rfc5961 challenge ack rate limiting */
+-int sysctl_tcp_challenge_ack_limit = 100;
++int sysctl_tcp_challenge_ack_limit = 1000;
+ 
+ int sysctl_tcp_stdurg __read_mostly;
+ int sysctl_tcp_rfc1337 __read_mostly;
+@@ -3715,13 +3715,20 @@ static void tcp_send_challenge_ack(struc
+ 	/* unprotected vars, we dont care of overwrites */
+ 	static u32 challenge_timestamp;
+ 	static unsigned int challenge_count;
+-	u32 now = jiffies / HZ;
++	u32 count, now = jiffies / HZ;
+ 
+ 	if (now != challenge_timestamp) {
++		u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;
++
+ 		challenge_timestamp = now;
+-		challenge_count = 0;
+-	}
+-	if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
++		ACCESS_ONCE(challenge_count) =
++			half + (u32)(
++			((u64) random32() * sysctl_tcp_challenge_ack_limit)
++			>> 32);
++	}
++	count = ACCESS_ONCE(challenge_count);
++	if (count > 0) {
++		ACCESS_ONCE(challenge_count) = count - 1;
+ 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+ 		tcp_send_ack(sk);
+ 	}

This was sent by the SourceForge.net collaborative development platform, the world's largest Open Source development site.