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

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Date:	Mon, 09 Sep 2013 09:26:07 +0300
From:	Matti Vaittinen <matti.vaittinen@....com>
To:	Daniel Borkmann <dborkman@...hat.com>, davem@...emloft.net,
	netdev@...r.kernel.org, Lin Ming <mlin@...pku.edu.cn>
Subject: Re: [PATCH net] net: fib: fib6_add: fix potential NULL pointer dereference

On 09/07/2013 10:35 PM, ext Hannes Frederic Sowa wrote:
> 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>
>
Acked-by: Matti Vaittinen <matti.vaittinen@....com>
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