linux-kernel - Re: [PATCH] net/mlx4_en: Fix an use-after-free bug in mlx4_en_try_alloc

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Date:   Wed, 1 Dec 2021 11:27:43 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     kjlu@....edu, Tariq Toukan <tariqt@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eugenia Emantayev <eugenia@...lanox.com>,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/mlx4_en: Fix an use-after-free bug in
 mlx4_en_try_alloc_resources()

On Wed, Dec 01, 2021 at 12:44:38AM +0800, Zhou Qingyang wrote:
> In mlx4_en_try_alloc_resources(), mlx4_en_copy_priv() is called and
> tmp->tx_cq will be freed on the error path of mlx4_en_copy_priv().
> After that mlx4_en_alloc_resources() is called and there is a dereference
> of &tmp->tx_cq[t][i] in mlx4_en_alloc_resources(), which could lead to
> a use after free problem on failure of mlx4_en_copy_priv().
> 
> Fix this bug by adding a check of mlx4_en_copy_priv()
> 
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
> 
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
> 
> Builds with CONFIG_MLX4_EN=m show no new warnings,
> and our static analyzer no longer warns about this code.
> 
> Fixes: ec25bc04ed8e ("net/mlx4_en: Add resilience in low memory systems")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 

Thanks,
Reviewed-by: Leon Romanovsky <leonro@...dia.com>