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

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Message-ID: <20180709191814.GA26059@ziepe.ca>
Date:   Mon, 9 Jul 2018 13:18:14 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jann Horn <jannh@...gle.com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] IB/mlx5: fix uaccess beyond "count" in debugfs
 read/write handlers

On Fri, Jul 06, 2018 at 10:48:03PM +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 the read handlers check that *pos is zero
> (meaning that at least sys_splice() can't trigger kernel memory
> corruption). Because of the root requirement, this is not a security fix,
> but rather a cleanup.
> 
> For the read handlers, fix it by using simple_read_from_buffer() instead of
> custom logic. Add min() calls to the write handlers.
> 
> changed in v2:
>  - also fix write handlers
> 
> Fixes: 4a2da0b8c078 ("IB/mlx5: Add debug control parameters for congestion control")
> Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
> Signed-off-by: Jann Horn <jannh@...gle.com>
> Reviewed-by: Leon Romanovsky <leonro@...lanox.com>
> ---
>  drivers/infiniband/hw/mlx5/cong.c |  9 +--------
>  drivers/infiniband/hw/mlx5/mr.c   | 32 ++++++++-----------------------
>  2 files changed, 9 insertions(+), 32 deletions(-)

Applied to for-next

Thanks,
Jason