netdev - Re: net: socket: NULL ptr deref in sendmsg

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Date:	Sat, 26 Jul 2014 19:40:51 +0400
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: net: socket: NULL ptr deref in sendmsg

2014-07-26 0:52 GMT+04:00 Sasha Levin <sasha.levin@...cle.com>:
> On 07/25/2014 11:23 AM, Andrey Ryabinin wrote:
>> After this report there was no usual "Unable to handle kernel NULL pointer dereference"
>> and this gave me a clue that address 0 is mapped and contains valid socket address structure in it.
>
> Interesting. Does it mean that all network protocols that check it for being NULL instead of checking
> the length are incorrect?
>

I think they are correct. After verify_iovec() we should have either
both msg->msg_name == 0 and msg->msg_namelen == 0,
or  both != 0 (and msg_name should be a kernel address).

That bug allows to leave verify_iovec() with msg_namelen > 0 and
msg_name == NULL, causing troubles for protocols checking only
msg_namelen.

> (such as:)
>
>         if (msg->msg_name) {
>                 DECLARE_SOCKADDR(struct sockaddr_can *, addr, msg->msg_name);
>
>                 [...]
>
>
> Thanks,
> Sasha
>

-- 
Best regards,
Andrey Ryabinin
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