This is a note to let you know that I've just added the patch titled
ipv6: make exception cache less predictible
to the 4.19-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:
ipv6-make-exception-cache-less-predictible.patch
and it can be found in the queue-4.19 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 Fri Oct 29 05:03:15 PM CEST 2021
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Sun, 29 Aug 2021 15:16:14 -0700
Subject: ipv6: make exception cache less predictible
From: Eric Dumazet <edumazet@xxxxxxxxxx>
commit a00df2caffed3883c341d5685f830434312e4a43 upstream.
Even after commit 4785305c05b2 ("ipv6: use siphash in rt6_exception_hash()"),
an attacker can still use brute force to learn some secrets from a victim
linux host.
One way to defeat these attacks is to make the max depth of the hash
table bucket a random value.
Before this patch, each bucket of the hash table used to store exceptions
could contain 6 items under attack.
After the patch, each bucket would contains a random number of items,
between 6 and 10. The attacker can no longer infer secrets.
This is slightly increasing memory size used by the hash table,
we do not expect this to be a problem.
Following patch is dealing with the same issue in IPv4.
Fixes: 35732d01fe31 ("ipv6: introduce a hash table to store dst cache")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Keyu Man <kman001@xxxxxxx>
Cc: Wei Wang <weiwan@xxxxxxxxxx>
Cc: Martin KaFai Lau <kafai@xxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[OP: adjusted context for 4.19 stable]
Signed-off-by: Ovidiu Panait <ovidiu.panait@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv6/route.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1454,6 +1454,7 @@ static int rt6_insert_exception(struct r
struct rt6_exception_bucket *bucket;
struct in6_addr *src_key = NULL;
struct rt6_exception *rt6_ex;
+ int max_depth;
int err = 0;
spin_lock_bh(&rt6_exception_lock);
@@ -1515,7 +1516,9 @@ static int rt6_insert_exception(struct r
bucket->depth++;
net->ipv6.rt6_stats->fib_rt_cache++;
- if (bucket->depth > FIB6_MAX_DEPTH)
+ /* Randomize max depth to avoid some side channels attacks. */
+ max_depth = FIB6_MAX_DEPTH + prandom_u32_max(FIB6_MAX_DEPTH);
+ while (bucket->depth > max_depth)
rt6_exception_remove_oldest(bucket);
out:
Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are
queue-4.19/ipv6-use-siphash-in-rt6_exception_hash.patch
queue-4.19/ipv6-make-exception-cache-less-predictible.patch
queue-4.19/ipv4-use-siphash-instead-of-jenkins-in-fnhe_hashfun.patch
