Commit 0409c9a5 authored Jan 05, 2015 by Daniel Borkmann Committed by David S. Miller Jan 05, 2015

net: fib6: fib6_commit_metrics: fix potential NULL pointer dereference



When IPv6 host routes with metrics attached are being added, we fetch
the metrics store from the dst via COW through dst_metrics_write_ptr(),
added through commit e5fd387a.

One remaining problem here is that we actually call into inet_getpeer()
and may end up allocating/creating a new peer from the kmemcache, which
may fail.

Example trace from perf probe (inet_getpeer:41) where create is 1:

ip 6877 [002] 4221.391591: probe:inet_getpeer: (ffffffff8165e293)
  85e294 inet_getpeer.part.7 (<- kmem_cache_alloc())
  85e578 inet_getpeer
  8eb333 ipv6_cow_metrics
  8f10ff fib6_commit_metrics

Therefore, a check for NULL on the return of dst_metrics_write_ptr()
is necessary here.

Joint work with Florian Westphal.

Fixes: e5fd387a ("ipv6: do not overwrite inetpeer metrics prematurely")
Cc: Michal Kubeček <mkubecek@suse.cz>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 6cb69742

net/ipv6/ip6_fib.c

+6 −7

Original line number	Diff line number	Diff line
		@@ -633,18 +633,17 @@ static bool rt6_qualify_for_ecmp(struct rt6_info *rt)
		static int fib6_commit_metrics(struct dst_entry *dst,
		struct nlattr *mx, int mx_len)
		{
		bool dst_host = dst->flags & DST_HOST;
		struct nlattr *nla;
		int remaining;
		u32 *mp;

		if (dst->flags & DST_HOST) {
		mp = dst_metrics_write_ptr(dst);
		} else {
		mp = kzalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
		if (!mp)
		mp = dst_host ? dst_metrics_write_ptr(dst) :
		kzalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
		if (unlikely(!mp))
		return -ENOMEM;
		if (!dst_host)
		dst_init_metrics(dst, mp, 0);
		}

		nla_for_each_attr(nla, mx, mx_len, remaining) {
		int type = nla_type(nla);

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