netdev - Re: [PATCH net] net: fib: fib6_add: fix potential NULL pointer dereference

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Date:	Sat, 7 Sep 2013 21:35:57 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Lin Ming <mlin@...pku.edu.cn>,
	Matti Vaittinen <matti.vaittinen@....com>
Subject: Re: [PATCH net] net: fib: fib6_add: fix potential NULL pointer dereference

On Sat, Sep 07, 2013 at 03:13:20PM +0200, Daniel Borkmann wrote:
> When the kernel is compiled with CONFIG_IPV6_SUBTREES, and we return
> with an error in fn = fib6_add_1(), then error codes are encoded into
> the return pointer e.g. ERR_PTR(-ENOENT). In such an error case, we
> write the error code into err and jump to out, hence enter the if(err)
> condition. Now, if CONFIG_IPV6_SUBTREES is enabled, we check for:
> 
>   if (pn != fn && pn->leaf == rt)
>     ...
>   if (pn != fn && !pn->leaf && !(pn->fn_flags & RTN_RTINFO))
>     ...
> 
> Since pn is NULL and fn is f.e. ERR_PTR(-ENOENT), then pn != fn
> evaluates to true and causes a NULL-pointer dereference on further
> checks on pn. Fix it, by setting both NULL in error case, so that
> pn != fn already evaluates to false and no further dereference
> takes place.
> 
> This was first correctly implemented in 4a287eba2 ("IPv6 routing,
> NLM_F_* flag support: REPLACE and EXCL flags support, warn about
> missing CREATE flag"), but the bug got later on introduced by
> 188c517a0 ("ipv6: return errno pointers consistently for fib6_add_1()").
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Cc: Lin Ming <mlin@...pku.edu.cn>
> Cc: Matti Vaittinen <matti.vaittinen@....com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>

Full ACK!

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

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