This is a note to let you know that I've just added the patch titled
[PATCH stable 5.8 10/25] icmp: randomize the global rate limiter
to the 5.8-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:
icmp-randomize-the-global-rate-limiter.patch
and it can be found in the queue-5.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Sat Oct 24 10:56:27 AM CEST 2020
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Thu, 15 Oct 2020 11:42:00 -0700
Subject: [PATCH stable 5.8 10/25] icmp: randomize the global rate limiter
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit b38e7819cae946e2edf869e604af1e65a5d241c5 ]
Keyu Man reported that the ICMP rate limiter could be used
by attackers to get useful signal. Details will be provided
in an upcoming academic publication.
Our solution is to add some noise, so that the attackers
no longer can get help from the predictable token bucket limiter.
Fixes: 4cdf507d5452 ("icmp: add a global rate limitation")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Keyu Man <kman001@xxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
Documentation/networking/ip-sysctl.rst | 4 +++-
net/ipv4/icmp.c | 7 +++++--
2 files changed, 8 insertions(+), 3 deletions(-)
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1142,13 +1142,15 @@ icmp_ratelimit - INTEGER
icmp_msgs_per_sec - INTEGER
Limit maximal number of ICMP packets sent per second from this host.
Only messages whose type matches icmp_ratemask (see below) are
- controlled by this limit.
+ controlled by this limit. For security reasons, the precise count
+ of messages per second is randomized.
Default: 1000
icmp_msgs_burst - INTEGER
icmp_msgs_per_sec controls number of ICMP packets sent per second,
while icmp_msgs_burst controls the burst size of these packets.
+ For security reasons, the precise burst size is randomized.
Default: 50
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -239,7 +239,7 @@ static struct {
/**
* icmp_global_allow - Are we allowed to send one more ICMP message ?
*
- * Uses a token bucket to limit our ICMP messages to sysctl_icmp_msgs_per_sec.
+ * Uses a token bucket to limit our ICMP messages to ~sysctl_icmp_msgs_per_sec.
* Returns false if we reached the limit and can not send another packet.
* Note: called with BH disabled
*/
@@ -267,7 +267,10 @@ bool icmp_global_allow(void)
}
credit = min_t(u32, icmp_global.credit + incr, sysctl_icmp_msgs_burst);
if (credit) {
- credit--;
+ /* We want to use a credit of one in average, but need to randomize
+ * it for security reasons.
+ */
+ credit = max_t(int, credit - prandom_u32_max(3), 0);
rc = true;
}
WRITE_ONCE(icmp_global.credit, credit);
Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are
queue-5.8/icmp-randomize-the-global-rate-limiter.patch
queue-5.8/net-properly-typecast-int-values-to-set-sk_max_pacing_rate.patch
queue-5.8/tcp-fix-to-update-snd_wl1-in-bulk-receiver-fast-path.patch
queue-5.8/net-ipv4-always-honour-route-mtu-during-forwarding.patch
