linux-kernel - Re: [PATCH] ipv6: ip6_fib: fix possible null-pointer-dereference in ipv6_route_native_seq

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Message-ID: <17db0b5f-a0aa-448a-8fdf-a1264dcf95d0@kernel.org>
Date: Tue, 5 Nov 2024 08:44:10 -0700
From: David Ahern <dsahern@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>, Yi Zou <03zouyi09.25@...il.com>,
 davem@...emloft.net
Cc: 21210240012@...udan.edu.cn, 21302010073@...udan.edu.cn,
 edumazet@...gle.com, kuba@...nel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: ip6_fib: fix possible null-pointer-dereference in
 ipv6_route_native_seq_show

On 11/5/24 5:28 AM, Paolo Abeni wrote:
> 
> 
> On 11/1/24 05:48, Yi Zou wrote:
>> In the ipv6_route_native_seq_show function, the fib6_nh variable
>> is assigned the value from nexthop_fib6_nh(rt->nh), which could
>> return NULL. This creates a risk of a null-pointer-dereference
>> when accessing fib6_nh->fib_nh_gw_family. This can be resolved by
>> checking if fib6_nh is non-NULL before accessing fib6_nh->fib_nh_gw_family
>>  and assign dev using dev = fib6_nh ? fib6_nh->fib_nh_dev : NULL;
>> to prevent null-pointer dereference errors.
>>
>> Signed-off-by: Yi Zou <03zouyi09.25@...il.com>
> 
> Please send a new revision, including a the target tree in the subj
> prefix - in this case 'net' and a suitable Fixes tag.
> 
> /P
> 

I would also like to understand why you believe NULL can really happen -
excluding memory corruption or custom patches to a kernel. If you look
at the make up of nexthop_fib6_nh it is defensive around bugs elsewhere
(nhsel > number of nexthops) and future changes (support for ipv6
nexthops that are not IPV6 addresses).

That comment applies to all of these patches around nexthop_fib6_nh
possibly returning NULL.