+++ /dev/null
-From 5413f1a526d2d51d7a5768133c90936c017165c6 Mon Sep 17 00:00:00 2001
-From: Jason Baron <jbaron@akamai.com>
-Date: Thu, 14 Jul 2016 11:38:40 -0400
-Subject: [PATCH] tcp: enable per-socket rate limiting of all 'challenge acks'
-
-[ Upstream commit 083ae308280d13d187512b9babe3454342a7987e ]
-
-The per-socket rate limit for 'challenge acks' was introduced in the
-context of limiting ack loops:
-
-commit f2b2c582e824 ("tcp: mitigate ACK loops for connections as tcp_sock")
-
-And I think it can be extended to rate limit all 'challenge acks' on a
-per-socket basis.
-
-Since we have the global tcp_challenge_ack_limit, this patch allows for
-tcp_challenge_ack_limit to be set to a large value and effectively rely on
-the per-socket limit, or set tcp_challenge_ack_limit to a lower value and
-still prevents a single connections from consuming the entire challenge ack
-quota.
-
-It further moves in the direction of eliminating the global limit at some
-point, as Eric Dumazet has suggested. This a follow-up to:
-Subject: tcp: make challenge acks less predictable
-
-CVE: CVE-2016-5696
-Upstream-Status: Backport
-
-Cc: Eric Dumazet <edumazet@google.com>
-Cc: David S. Miller <davem@davemloft.net>
-Cc: Neal Cardwell <ncardwell@google.com>
-Cc: Yuchung Cheng <ycheng@google.com>
-Cc: Yue Cao <ycao009@ucr.edu>
-Signed-off-by: Jason Baron <jbaron@akamai.com>
-Signed-off-by: David S. Miller <davem@davemloft.net>
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-Signed-off-by: Sona Sarmadi <sona.sarmadi@enea.com>
-Signed-off-by: Adrian Dudau <adrian.dudau@enea.com>
-
----
- net/ipv4/tcp_input.c | 39 ++++++++++++++++++++++-----------------
- 1 file changed, 22 insertions(+), 17 deletions(-)
-
-diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
-index 05f10df..12b98e2 100644
---- a/net/ipv4/tcp_input.c
-+++ b/net/ipv4/tcp_input.c
-@@ -3390,6 +3390,23 @@ static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32
- return flag;
- }
-
-+static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
-+ u32 *last_oow_ack_time)
-+{
-+ if (*last_oow_ack_time) {
-+ s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
-+
-+ if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
-+ NET_INC_STATS_BH(net, mib_idx);
-+ return true; /* rate-limited: don't send yet! */
-+ }
-+ }
-+
-+ *last_oow_ack_time = tcp_time_stamp;
-+
-+ return false; /* not rate-limited: go ahead, send dupack now! */
-+}
-+
- /* Return true if we're currently rate-limiting out-of-window ACKs and
- * thus shouldn't send a dupack right now. We rate-limit dupacks in
- * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
-@@ -3403,21 +3420,9 @@ bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
- /* Data packets without SYNs are not likely part of an ACK loop. */
- if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
- !tcp_hdr(skb)->syn)
-- goto not_rate_limited;
--
-- if (*last_oow_ack_time) {
-- s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
--
-- if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
-- NET_INC_STATS_BH(net, mib_idx);
-- return true; /* rate-limited: don't send yet! */
-- }
-- }
--
-- *last_oow_ack_time = tcp_time_stamp;
-+ return false;
-
--not_rate_limited:
-- return false; /* not rate-limited: go ahead, send dupack now! */
-+ return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
- }
-
- /* RFC 5961 7 [ACK Throttling] */
-@@ -3430,9 +3435,9 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
- u32 count, now;
-
- /* First check our per-socket dupack rate limit. */
-- if (tcp_oow_rate_limited(sock_net(sk), skb,
-- LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
-- &tp->last_oow_ack_time))
-+ if (__tcp_oow_rate_limited(sock_net(sk),
-+ LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
-+ &tp->last_oow_ack_time))
- return;
-
- /* Then check host-wide RFC 5961 rate limit. */
---
-1.9.1
-
+++ /dev/null
-From 72c2d3bccaba4a0a4de354f9d2d24eccd05bfccf Mon Sep 17 00:00:00 2001
-From: Eric Dumazet <edumazet@google.com>
-Date: Sun, 10 Jul 2016 10:04:02 +0200
-Subject: [PATCH] tcp: make challenge acks less predictable
-
-[ Upstream commit 75ff39ccc1bd5d3c455b6822ab09e533c551f758 ]
-
-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.
-
-CVE: CVE-2016-5696
-Upstream-Status: Backport
-
-Fixes: 282f23c6ee34 ("tcp: implement RFC 5961 3.2")
-Reported-by: Yue Cao <ycao009@ucr.edu>
-Signed-off-by: Eric Dumazet <edumazet@google.com>
-Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
-Cc: Yuchung Cheng <ycheng@google.com>
-Cc: Neal Cardwell <ncardwell@google.com>
-Acked-by: Neal Cardwell <ncardwell@google.com>
-Acked-by: Yuchung Cheng <ycheng@google.com>
-Signed-off-by: David S. Miller <davem@davemloft.net>
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-Signed-off-by: Sona Sarmadi <sona.sarmadi@enea.com>
-Signed-off-by: Adrian Dudau <adrian.dudau@enea.com>
-
----
- 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 d4c5115..05f10df 100644
---- a/net/ipv4/tcp_input.c
-+++ b/net/ipv4/tcp_input.c
-@@ -89,7 +89,7 @@ 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;
-@@ -3427,7 +3427,7 @@ 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,
-@@ -3435,13 +3435,18 @@ 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);
- }
---
-1.9.1
-
