netdev - IPv6: finding a match in find_rr_leaf that cause a NULL pointer dereference

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Message-ID: <loom.20150527T081417-915@post.gmane.org>
Date:	Wed, 27 May 2015 06:28:19 +0000 (UTC)
From:	Jeremy <poseng@...il.com>
To:	netdev@...r.kernel.org
Subject: IPv6: finding a match in find_rr_leaf that cause a NULL pointer dereference

Hi all,

My kernel is 3.10.20 and I encountered this NULL pointer dereference.

According to my log, I found that dev is NULL in the beginning of for 
loop. it is the dev of rr_head that has been set to NULL. That might be 
possible that dev being NULL but I don't see any case to avoid such case 
in rt6_check_dev(), even the kernel 4.0.

Don't know if my concern is necessary or not or there has a mechanism in 
somewhere that I hadn't been noticed.

Any comment of my concern is welcome and thanks for your time to review my 
post.

for (rt = rr_head; rt && rt->rt6i_metric == metric; rt = rt->dst.rt6_next)
    match = find_match(rt, oif, strict, &mpri, match, do_rr);
  --> rt6_score_route(rt, oif, strict);
    --> rt6_check_dev(rt, oif);
     --> struct net_device *dev = rt->dst.dev;
     --> if (!oif || dev->ifindex == oif) <------NULL pointer dereference 
on dev object.

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