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From: Bart Van Assche <bvanassche@acm.org>
To: zhengbin <zhengbin13@huawei.com>,
	jejb@linux.ibm.com, martin.petersen@oracle.com,
	linux-scsi@vger.kernel.org
Cc: yi.zhang@huawei.com
Subject: Re: [PATCH] scsi: core: fix uninit-value access of variable sshdr
Date: Thu, 10 Oct 2019 10:03:29 -0700
Message-ID: <fe58cc1c-f15a-2b05-24b7-24d9ef6f4f34@acm.org> (raw)
In-Reply-To: <1570709143-147364-1-git-send-email-zhengbin13@huawei.com>

On 10/10/19 5:05 AM, zhengbin wrote:
> kmsan report a warning in 5.1-rc4:
> 
> BUG: KMSAN: uninit-value in sr_get_events drivers/scsi/sr.c:207 [inline]
> BUG: KMSAN: uninit-value in sr_check_events+0x2cf/0x1090 drivers/scsi/sr.c:243
> CPU: 1 PID: 13858 Comm: syz-executor.0 Tainted: G    B             5.1.0-rc4+ #8
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x173/0x1d0 lib/dump_stack.c:113
>   kmsan_report+0x131/0x2a0 mm/kmsan/kmsan.c:619
>   __msan_warning+0x7a/0xf0 mm/kmsan/kmsan_instr.c:310
>   sr_get_events drivers/scsi/sr.c:207 [inline]
>   sr_check_events+0x2cf/0x1090 drivers/scsi/sr.c:243
> 
> The reason is as follows:
> sr_get_events
>    struct scsi_sense_hdr sshdr;  -->uninit
>    scsi_execute_req              -->If fail, will not set sshdr
>    scsi_sense_valid(&sshdr)      -->access sshdr
> 
> We can init sshdr in sr_get_events, but there have many callers of
> scsi_execute, scsi_execute_req, we have to troubleshoot all callers,
> the simpler way is init sshdr in __scsi_execute.
> 
> BTW: we can't just init sshdr->response_code, sr_do_ioctl use
> sshdr->sense_key(Need to troubleshoot all callers)
> 
> Signed-off-by: zhengbin <zhengbin13@huawei.com>
> ---
>   drivers/scsi/scsi_lib.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 5447738..037fb2a 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -255,6 +255,12 @@ int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>   	struct scsi_request *rq;
>   	int ret = DRIVER_ERROR << 24;
> 
> +	/*
> +	 * need to initial sshdr to avoid uninit-value access
> +	 */
> +	if (sshdr)
> +		memset(sshdr, 0, sizeof(struct scsi_sense_hdr));
> +
>   	req = blk_get_request(sdev->request_queue,
>   			data_direction == DMA_TO_DEVICE ?
>   			REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN, BLK_MQ_REQ_PREEMPT);

 From SAM-5: "Sense data shall be made available by the logical unit if 
a command terminates with CHECK CONDITION status or other conditions 
(e.g., the processing of a REQUEST SENSE command). The format, content, 
and conditions under which sense data shall be prepared by the logical 
unit are as defined in this standard, SPC-4, the applicable command 
standard, and the applicable SCSI transport protocol standard."

Apparently sr_check_events() submits a GET EVENT STATUS NOTIFICATION 
command and it even evaluates the sense data if that command succeeded. 
I'm not aware of other scsi_execute() callers that do this. So I'm not 
sure that modifying __scsi_execute() is the best approach. I'm wondering 
whether the sr driver should be fixed instead of modifying __scsi_execute().

Thanks,

Bart.

  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-10 12:05 zhengbin
2019-10-10 17:03 ` Bart Van Assche [this message]
2019-10-11  3:07   ` zhengbin (A)
2019-10-11 17:15     ` Bart Van Assche
2019-10-11 17:17 ` Bart Van Assche

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