linux-kernel - Re: [PATCH net v2] net/mlx5: fix uaccess beyond "count" in debugfs read/write handlers

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Date:   Wed, 11 Jul 2018 19:10:38 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "jannh@...gle.com" <jannh@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "leon@...nel.org" <leon@...nel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH net v2] net/mlx5: fix uaccess beyond "count" in debugfs
 read/write handlers

On Fri, 2018-07-06 at 22:18 +0200, Jann Horn wrote:
> In general, accessing userspace memory beyond the length of the
> supplied
> buffer in VFS read/write handlers can lead to both kernel memory
> corruption
> (via kernel_read()/kernel_write(), which can e.g. be triggered via
> sys_splice()) and privilege escalation inside userspace.
> 
> In this case, the affected files are in debugfs (and should therefore
> only
> be accessible to root) and check that *pos is zero (which prevents
> the
> sys_splice() trick). Therefore, this is not a security fix, but
> rather a
> small cleanup.
> 
> For the read handlers, fix it by using simple_read_from_buffer()
> instead of
> custom logic.
> For the write handler, add a check.
> 
> changed in v2:
>  - also fix dbg_write()
> 
> Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB
> adapters")
> Signed-off-by: Jann Horn <jannh@...gle.com>
> 

Applied to mlx5-next, Thanks!!