Re: [PATCH v3] scsi: core: fix uninit-value access of variable sshdr

[Finn Thain <fthain@telegraphics.com.au>]

On Sat, 12 Oct 2019, 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: sr_do_ioctl should check whether sshdr is valid, fix this
> 
> Signed-off-by: zhengbin <zhengbin13@huawei.com>
> ---
> v1->v2: modify the comments suggested by Bart
> v2->v3: fix bug in sr_do_ioctl
>  drivers/scsi/scsi_lib.c | 7 +++++++
>  drivers/scsi/sr_ioctl.c | 5 +++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 5447738..d5e29c5 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -255,6 +255,13 @@ int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>  	struct scsi_request *rq;
>  	int ret = DRIVER_ERROR << 24;
> 
> +	/*
> +	 * Zero-initialize sshdr for those callers that check the *sshdr
> +	 * contents even if no sense data is available.
> +	 */
> +	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);

Does this have any effect? It appears __scsi_execute() calls 
scsi_normalize_sense(), which already does
memset(sshdr, 0, sizeof(struct scsi_sense_hdr)).

-- 

> diff --git a/drivers/scsi/sr_ioctl.c b/drivers/scsi/sr_ioctl.c
> index ffcf902..335cfdd 100644
> --- a/drivers/scsi/sr_ioctl.c
> +++ b/drivers/scsi/sr_ioctl.c
> @@ -206,6 +206,11 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
> 
>  	/* Minimal error checking.  Ignore cases we know about, and report the rest. */
>  	if (driver_byte(result) != 0) {
> +		if (!scsi_sense_valid(sshdr)) {
> +			err = -EIO;
> +			goto out;
> +		}
> +
>  		switch (sshdr->sense_key) {
>  		case UNIT_ATTENTION:
>  			SDev->changed = 1;
> --
> 2.7.4
> 
>