linux-kernel - Re: [PATCH] potential NULL pointer deref in net/key/af

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Date:	Mon, 27 Nov 2006 13:53:33 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jesper.juhl@...il.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	gem@...linux.ru, davem@...hat.com, kuznet@....inr.ac.ru,
	kunihiro@...nfusion.com, miyazawa@...ux-ipv6.org, derek@...fp.com
Subject: Re: [PATCH] potential NULL pointer deref in net/key/af_key.c

From: Jesper Juhl <jesper.juhl@...il.com>
Date: Mon, 27 Nov 2006 22:44:07 +0100

> In net/key/af_key.c::pfkey_send_policy_notify() there's a check at the 
> beginning of the function : 
> 
>     if (xp && xp->type != XFRM_POLICY_TYPE_MAIN)
> 
> this implies that 'xp' may be null when the function is called. But later 
> on in the function we have this code : 
> 
>     return key_notify_policy(xp, dir, c);
> 
> key_notify_policy() passes 'xp' to pfkey_xfrm_policy2msg_prep() that pass
> it on to pfkey_xfrm_policy2msg_size() which dereferences it.
> key_notify_policy() also passes 'xp' to pfkey_xfrm_policy2msg() which 
> also dereferences it.
> 
> So, in pfkey_send_policy_notify() in the cases where we end up calling 
> key_notify_policy(), we should test 'xp' for NULL.
> 
> (note: patch is compile tested only)
> 
> 
> Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>

We really need to teach your automated tool about context.

The NULL case can only occur for XFRM_MSG_FLUSHPOLICY.

Look at the km_policy_notify() call sites.  You can even see from the
net/xfrm/xfrm_user.c:xfrm_send_policy_notify() implementation of this
callback that for XFRM_MSG_FLUSHPOLICY the "xp" argument is ignored.
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