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Date: Wed, 3 Dec 2025 17:55:19 +0000
From: Simon Horman <horms@kernel.org>
To: Petr Machata <petrm@nvidia.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Andrew Lunn <andrew+netdev@lunn.ch>, netdev@vger.kernel.org,
	Ido Schimmel <idosch@nvidia.com>, mlxsw@nvidia.com,
	Jiri Pirko <jiri@resnulli.us>
Subject: Re: [PATCH net 2/3] mlxsw: spectrum_router: Fix neighbour
 use-after-free
Message-ID: <aTB5h090Hu9BHFJ1@horms.kernel.org>
References: <cover.1764695650.git.petrm@nvidia.com>
 <92d75e21d95d163a41b5cea67a15cd33f547cba6.1764695650.git.petrm@nvidia.com>
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In-Reply-To: <92d75e21d95d163a41b5cea67a15cd33f547cba6.1764695650.git.petrm@nvidia.com>

On Tue, Dec 02, 2025 at 06:44:12PM +0100, Petr Machata wrote:
> From: Ido Schimmel <idosch@nvidia.com>
> 
> We sometimes observe use-after-free when dereferencing a neighbour [1].
> The problem seems to be that the driver stores a pointer to the
> neighbour, but without holding a reference on it. A reference is only
> taken when the neighbour is used by a nexthop.
> 
> Fix by simplifying the reference counting scheme. Always take a
> reference when storing a neighbour pointer in a neighbour entry. Avoid
> taking a referencing when the neighbour is used by a nexthop as the
> neighbour entry associated with the nexthop already holds a reference.
> 
> Tested by running the test that uncovered the problem over 300 times.
> Without this patch the problem was reproduced after a handful of
> iterations.

...

> Fixes: 6cf3c971dc84 ("mlxsw: spectrum_router: Add private neigh table")
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
> Reviewed-by: Petr Machata <petrm@nvidia.com>
> Signed-off-by: Petr Machata <petrm@nvidia.com>


Reviewed-by: Simon Horman <horms@kernel.org>


...