If two router advertisment speaker announce seperate default gateways with infinite timeout the kernel currently packs these routes together into an ecmp route set. If one of the RA speaker now changes the advertised expiration to a lower value and a third route with infinite timeout pops up we end up with a BUG_ON. Remote attacker could use this flaw to crash the system. Fixed by: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=307f2fb95e9b96b3577916e73d92e104f8f26494 Introduced by: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=51ebd3181572af8d5076808dab2682d800f6da5d Introduced in upstream version: v3.7-rc1 Acknowledgements: Red Hat would like to thank Hannes Frederic Sowa for reporting this issue. diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c index 192dd1a..5fc9c7a 100644 --- a/net/ipv6/ip6_fib.c +++ b/net/ipv6/ip6_fib.c @@ -632,6 +632,12 @@ insert_above: return ln; } +static inline bool rt6_qualify_for_ecmp(struct rt6_info *rt) +{ + return (rt->rt6i_flags & (RTF_GATEWAY|RTF_ADDRCONF|RTF_DYNAMIC)) == + RTF_GATEWAY; +} + /* * Insert routing information in a node. */ @@ -646,6 +652,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt, int add = (!info->nlh || (info->nlh->nlmsg_flags & NLM_F_CREATE)); int found = 0; + bool rt_can_ecmp = rt6_qualify_for_ecmp(rt); ins = &fn->leaf; @@ -691,9 +698,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt, * To avoid long list, we only had siblings if the * route have a gateway. */ - if (rt->rt6i_flags & RTF_GATEWAY && - !(rt->rt6i_flags & RTF_EXPIRES) && - !(iter->rt6i_flags & RTF_EXPIRES)) + if (rt_can_ecmp && + rt6_qualify_for_ecmp(iter)) rt->rt6i_nsiblings++; } @@ -715,7 +721,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt, /* Find the first route that have the same metric */ sibling = fn->leaf; while (sibling) { - if (sibling->rt6i_metric == rt->rt6i_metric) { + if (sibling->rt6i_metric == rt->rt6i_metric && + rt6_qualify_for_ecmp(sibling)) { list_add_tail(&rt->rt6i_siblings, &sibling->rt6i_siblings); break;