linux-kernel - Re: [External] : Re: [PATCH] netfilter: ebtables: fix a NULL pointer dereference in ebt_do

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Message-ID: <e570492a-69c8-f3f7-460d-066bb8a6df0d@oracle.com>
Date:   Sun, 21 Aug 2022 00:48:22 +0530
From:   Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To:     Florian Westphal <fw@...len.de>
Cc:     syzkaller@...glegroups.com, george.kennedy@...cle.com,
        vegard.nossum@...cle.com, john.p.donnelly@...cle.com,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [External] : Re: [PATCH] netfilter: ebtables: fix a NULL pointer
 dereference in ebt_do_table()

On 20/08/22 9:56 pm, Florian Westphal wrote:
> Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com> wrote:
>> In ebt_do_table() function dereferencing 'private->hook_entry[hook]'
>> can lead to NULL pointer dereference. So add a check to prevent that.
> 
Hi Florian,

Thanks a lot for checking the patch.

> This looks incorrect, i.e. paperimg over the problem.
> 

Okay.

> If hook_entry[hook] is NULL, how did this make it to the eval loop?
>

When I run the reproducer and have 'private->hook_entry[hook]' printed, 
it was NULL, so thought of adding a NULL check to prevent the NULL 
dereference.

Attaching the C reproducer.

Regards,
Harshit


> I guess ebtables lacks a sanity check on incoming ruleset?
> 

View attachment "r.c" of type "text/plain" (44610 bytes)