[packages/kernel/LINUX_4_1] - untested CVE-2016-5696 fix

[arekm]

commit 5f3a47f5bb24f5b24ef2a9dc9954ed5221c8abcb
Author: Arkadiusz Miśkiewicz <arekm at maven.pl>
Date:   Thu Aug 11 00:14:22 2016 +0200

    - untested CVE-2016-5696 fix

 kernel-small_fixes.patch | 81 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
---
diff --git a/kernel-small_fixes.patch b/kernel-small_fixes.patch
index 0a5d601..f785fa9 100644
--- a/kernel-small_fixes.patch
+++ b/kernel-small_fixes.patch
@@ -114,3 +114,84 @@ index 29531ec..65fbfb7 100644
  		goto out_destroy_log;
  
 
+From 75ff39ccc1bd5d3c455b6822ab09e533c551f758 Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <edumazet at google.com>
+Date: Sun, 10 Jul 2016 10:04:02 +0200
+Subject: tcp: make challenge acks less predictable
+
+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 <ycao009 at ucr.edu>
+Signed-off-by: Eric Dumazet <edumazet at google.com>
+Suggested-by: Linus Torvalds <torvalds at linux-foundation.org>
+Cc: Yuchung Cheng <ycheng at google.com>
+Cc: Neal Cardwell <ncardwell at google.com>
+Acked-by: Neal Cardwell <ncardwell at google.com>
+Acked-by: Yuchung Cheng <ycheng at google.com>
+Signed-off-by: David S. Miller <davem at davemloft.net>
+---
+ net/ipv4/tcp_input.c | 15 ++++++++++-----
+ 1 file changed, 10 insertions(+), 5 deletions(-)
+
+diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
+index d6c8f4cd0..91868bb 100644
+--- a/net/ipv4/tcp_input.c
++++ b/net/ipv4/tcp_input.c
+@@ -87,7 +87,7 @@ int sysctl_tcp_adv_win_scale __read_mostly = 1;
+ 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;
+@@ -3458,7 +3458,7 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
+ 	static u32 challenge_timestamp;
+ 	static unsigned int challenge_count;
+ 	struct tcp_sock *tp = tcp_sk(sk);
+-	u32 now;
++	u32 count, now;
+ 
+ 	/* First check our per-socket dupack rate limit. */
+ 	if (tcp_oow_rate_limited(sock_net(sk), skb,
+@@ -3466,13 +3466,18 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
+ 				 &tp->last_oow_ack_time))
+ 		return;
+ 
+-	/* Then check the check host-wide RFC 5961 rate limit. */
++	/* Then check host-wide RFC 5961 rate limit. */
+ 	now = jiffies / HZ;
+ 	if (now != challenge_timestamp) {
++		u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;
++
+ 		challenge_timestamp = now;
+-		challenge_count = 0;
++		WRITE_ONCE(challenge_count, half +
++			   prandom_u32_max(sysctl_tcp_challenge_ack_limit));
+ 	}
+-	if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
++	count = READ_ONCE(challenge_count);
++	if (count > 0) {
++		WRITE_ONCE(challenge_count, count - 1);
+ 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+ 		tcp_send_ack(sk);
+ 	}
+-- 
+cgit v1.0-17-g0c1e3
+
================================================================

---- gitweb:

http://git.pld-linux.org/gitweb.cgi/packages/kernel.git/commitdiff/5f3a47f5bb24f5b24ef2a9dc9954ed5221c8abcb