linux-kernel - Re: [PATCH] bsg: remove read/write support

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Date:   Thu, 12 Jul 2018 08:04:29 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christoph Hellwig <hch@....de>
Cc:     torvalds@...ux-foundation.org, tonyb@...ernetics.com,
        jannh@...gle.com, linux-block@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bsg: remove read/write support

On 7/12/18 2:09 AM, Christoph Hellwig wrote:
> The code poses a security risk due to user memory access in ->release
> and had an API that can't be used reliably.  As far as we know it was
> never used for real, but if that turns out wrong we'll have to revert
> this commit and come up with a band aid.
> 
> Jann Horn did look software archives for users of this interface,
> and the only users found were example code in sg3_utils, and optional
> support in an optional module of the tgt user space iscsi target,
> which looks like a proof of concept extension of the /dev/sg
> read/write support.
> 
> Tony Battersby chimes in that the code is basically unsafe to use in
> general:
> 
>   The read/write interface on /dev/bsg is impossible to use safely
>   because the list of completed commands is per-device (bd->done_list)
>   rather than per-fd like it is with /dev/sg.  So if program A and
>   program B are both using the write/read interface on the same bsg
>   device, then their command responses will get mixed up, and program
>   A will read() some command results from program B and vice versa.
>   So no, I don't use read/write on /dev/bsg.  From a security standpoint,
>   it should definitely be fixed or removed.

Applied for 4.19.

-- 
Jens Axboe