linux-kernel - Re: [PATCH] scsi: core: initialize cmd->cmnd before it is used

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Message-ID: <da8d3418-b95c-203d-16c3-8c4086ceaf73@acm.org>
Date:   Mon, 1 Nov 2021 13:20:19 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>,
        linux-scsi@...r.kernel.org
Cc:     Christoph Hellwig <hch@....de>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+5516b30f5401d4dcbcae@...kaller.appspotmail.com,
        Doug Gilbert <dgilbert@...erlog.com>
Subject: Re: [PATCH] scsi: core: initialize cmd->cmnd before it is used

On 11/1/21 1:13 PM, Tadeusz Struk wrote:
> On 11/1/21 13:06, Bart Van Assche wrote:
>> This patch is a duplicate and has been posted before.
>>
>> Please take a look at https://lore.kernel.org/linux-scsi/20210904064534.1919476-1-qiulaibin@huawei.com/.
>>  From the replies to that email:
>> "> Thinking further about this: is there any code left that depends on
>>  > scsi_setup_scsi_cmnd() setting cmd->cmd_len? Can the cmd->cmd_len
>>  > assignment be removed from scsi_setup_scsi_cmnd()?
>>
>> cmd_len should never be 0 now, so I think we can remove it."
> 
> Thanks for quick response, but I'm not sure if statement
> "cmd_len should never be 0 now" is correct, because the cmd_len is
> in fact equal to 0 here and this BUG can be triggered on mainline, 5.14,
> and 5.10 stable kernels.

(+Doug Gilbert)

One of the functions in the call stack in the first message of this email
thread is sg_io(). I am not aware of any documentation that specifies whether
it is valid to set cmd_len in the sg_io header to zero. My opinion is that
the SG_IO implementation should either reject cmd_len == 0 or set cmd_len
to a valid value if it is zero.

Bart.