Re: [PATCH] ipv4: fix the rcu race between free_fib_info and ip_route_output_slow

From: "kun.jiang" <redacted>
Date: Tue, 22 May 2012 17:48:53 +0800

From: Yanmin Zhang <redacted>

We hit a kernel OOPS.

 ...

In function free_fib_info, we don't reset nexthop_nh->nh_dev to NULL before releasing
nh_dev. kfree_rcu(fi, rcu) would release the whole area.

Signed-off-by: Yanmin Zhang <redacted>
Signed-off-by: Kun Jiang <redacted>

This isn't a fix.  You're keeping around a pointer to a completely
released object, which is therefore illegal to dereference.

That's why we must set it to NULL, to catch such illegal accesses.