| Message ID | 20210829221615.2057201-2-eric.dumazet@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | inet: make exception handling less predictible | expand |
On 8/29/21 3:16 PM, Eric Dumazet wrote: > From: Eric Dumazet <edumazet@google.com> > > 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@google.com> > Reported-by: Keyu Man <kman001@ucr.edu> > Cc: Wei Wang <weiwan@google.com> > Cc: Martin KaFai Lau <kafai@fb.com> > --- > net/ipv6/route.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > Reviewed-by: David Ahern <dsahern@kernel.org>
On Sun, Aug 29, 2021 at 5:39 PM David Ahern <dsahern@gmail.com> wrote: > > On 8/29/21 3:16 PM, Eric Dumazet wrote: > > From: Eric Dumazet <edumazet@google.com> > > > > 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@google.com> > > Reported-by: Keyu Man <kman001@ucr.edu> > > Cc: Wei Wang <weiwan@google.com> > > Cc: Martin KaFai Lau <kafai@fb.com> > > --- > > net/ipv6/route.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > Reviewed-by: David Ahern <dsahern@kernel.org> > Reviewed-by: Wei Wang <weiwan@google.com> Thanks Eric!
diff --git a/net/ipv6/route.c b/net/ipv6/route.c index c5e8ecb96426bda619fe242351e40dcf6ff68bcf..60334030210192660a7fa141163f36af7489d0ae 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1657,6 +1657,7 @@ static int rt6_insert_exception(struct rt6_info *nrt, struct in6_addr *src_key = NULL; struct rt6_exception *rt6_ex; struct fib6_nh *nh = res->nh; + int max_depth; int err = 0; spin_lock_bh(&rt6_exception_lock); @@ -1711,7 +1712,9 @@ static int rt6_insert_exception(struct rt6_info *nrt, 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: