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authorEric Dumazet <edumazet@google.com>2020-10-15 11:42:00 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-10-29 09:03:01 +0100
commita9d0ba6aa7485aabed7b8f2ed5a3975684847e0b (patch)
tree1c371f3fdd3f8805f0559d7b1b13a3d037f255ba
parent94b7768760e9666a08273b61e42513e12abdcf14 (diff)
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icmp: randomize the global rate limiter
[ 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@google.com> Reported-by: Keyu Man <kman001@ucr.edu> Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--Documentation/networking/ip-sysctl.txt4
-rw-r--r--net/ipv4/icmp.c7
2 files changed, 8 insertions, 3 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 21ad4f3cece8..eac939abe6c4 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -868,12 +868,14 @@ 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
icmp_ratemask - INTEGER
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 9a9f49b55abd..c16c199d9cd9 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -246,7 +246,7 @@ 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
*/
@@ -274,7 +274,10 @@ 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);