linux-kernel - Re: [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length check

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Message-ID: <4728ef5e-0036-7de6-8b6f-f29885d76473@cumulusnetworks.com>
Date:   Sun, 5 Jul 2020 22:11:39 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Linus Lüssing <linus.luessing@...3.blue>
Cc:     netdev@...r.kernel.org, Roopa Prabhu <roopa@...ulusnetworks.com>,
        Martin Weinelt <martin@...uxlounge.net>,
        "David S . Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] bridge: mcast: Fix MLD2 Report IPv6 payload length
 check

On 7/5/20 10:08 PM, Linus Lüssing wrote:
> On Sun, Jul 05, 2020 at 09:33:13PM +0300, Nikolay Aleksandrov wrote:
>> On 05/07/2020 21:22, Linus Lüssing wrote:
>>> Commit e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in
>>> igmp3/mld2 report handling") introduced a small bug which would potentially
>>> lead to accepting an MLD2 Report with a broken IPv6 header payload length
>>> field.
>>>
>>> The check needs to take into account the 2 bytes for the "Number of
>>> Sources" field in the "Multicast Address Record" before reading it.
>>> And not the size of a pointer to this field.
>>>
>>> Fixes: e57f61858b7c ("net: bridge: mcast: fix stale nsrcs pointer in igmp3/mld2 report handling")
>>> Signed-off-by: Linus Lüssing <linus.luessing@...3.blue>
>>> ---
>>>   net/bridge/br_multicast.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>
>> I'd rather be more concerned with it rejecting a valid report due to wrong size. The ptr
>> size would always be bigger. :)
>>
>> Thanks!
>> Acked-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> 
> Aiy, you're right, it's the other way round. I'll update the
> commit message and send a v2 in a minute, with your Acked-by
> included.
> 

By the way, I can't verify at the moment, but I think we can drop that whole
hunk altogether since skb_header_pointer() is used and it will simply return
an error if there isn't enough data for nsrcs.