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Date: Thu, 27 Mar 2025 09:41:33 -0400
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Subject: Re: [PATCH] net: ipv6: Fix NULL dereference in ipv6_route_check_nh
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To: Sabrina Dubroca <sd@queasysnail.net>,
 Purva Yeshi <purvayeshi550@gmail.com>
Cc: "David S . Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
 Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
 netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20250326105215.23853-1-purvayeshi550@gmail.com>
 <Z-P5vvrdA5MHMW_o@krikkit>
From: David Ahern <dsahern@kernel.org>
In-Reply-To: <Z-P5vvrdA5MHMW_o@krikkit>
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On 3/26/25 6:57 AM, Sabrina Dubroca wrote:
> 2025-03-26, 16:22:15 +0530, Purva Yeshi wrote:
>> Fix Smatch-detected error:
>> net/ipv6/route.c:3427 ip6_route_check_nh() error:
>> we previously assumed '_dev' could be null
> 
> I don't think this can actually happen. ip6_route_check_nh only gets
> called via fib6_nh_init -> ip6_validate_gw -> ip6_route_check_nh, and
> ip6_validate_gw unconditionally does dev = *_dev. Which is fine,
> because its only caller (fib6_nh_init) passes &dev, so that can't be
> NULL (and same for idev).

And fib6_nh_init has:

        struct net_device *dev = NULL;
        struct inet6_dev *idev = NULL;

> 
>> Ensure _dev and idev are checked for NULL before dereferencing in
>> ip6_route_check_nh. Assign NULL explicitly when fib_nh_dev is NULL
>> to prevent unintended dereferences.
> 
> That's a separate issue (if it's really possible - I haven't checked)
> than the smatch report you're quoting above. And if it is, it would
> deserve a Fixes tag for the commit introducing this code.

I do not believe it is a problem.