[PATCH] usb: storage: Fix a possible data race in uas_queuecommand_lck

[PATCH] usb: storage: Fix a possible data race in uas_queuecommand_lck

[Jia-Ju Bai]

The write operations to "cmnd->result" and "cmnd->scsi_done" 
are protected by the lock on line 642-643, but the write operations 
to these data on line 634-635 are not protected by the lock.
Thus, there may exist a data race for "cmnd->result" 
and "cmnd->scsi_done".

To fix this data race, the write operations on line 634-635 
should be also protected by the lock.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/usb/storage/uas.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index 6034c39b67d1..dde7a43ad491 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -627,17 +627,18 @@ static int uas_queuecommand_lck(struct scsi_cmnd *cmnd,
 	if (cmnd->device->host->host_self_blocked)
 		return SCSI_MLQUEUE_DEVICE_BUSY;
 
+	spin_lock_irqsave(&devinfo->lock, flags);
+
 	if ((devinfo->flags & US_FL_NO_ATA_1X) &&
 			(cmnd->cmnd[0] == ATA_12 || cmnd->cmnd[0] == ATA_16)) {
 		memcpy(cmnd->sense_buffer, usb_stor_sense_invalidCDB,
 		       sizeof(usb_stor_sense_invalidCDB));
 		cmnd->result = SAM_STAT_CHECK_CONDITION;
 		cmnd->scsi_done(cmnd);
+		spin_unlock_irqrestore(&devinfo->lock, flags);
 		return 0;
 	}
 
-	spin_lock_irqsave(&devinfo->lock, flags);
-
 	if (devinfo->resetting) {
 		cmnd->result = DID_ERROR << 16;
 		cmnd->scsi_done(cmnd);
-- 
2.17.0

Re: [usb-storage] [PATCH] usb: storage: Fix a possible data race in uas_queuecommand_lck

[Oliver Neukum]

Am Dienstag, den 08.05.2018, 15:47 +0800 schrieb Jia-Ju Bai:
> The write operations to "cmnd->result" and "cmnd->scsi_done" 
> are protected by the lock on line 642-643, but the write operations 
> to these data on line 634-635 are not protected by the lock.
> Thus, there may exist a data race for "cmnd->result" 
> and "cmnd->scsi_done".

No,

the write operations need no lock. The low level driver at this point
owns the command. We cannot race with abort() for a command within
queuecommand(). We take the lock where we take it to protect
dev->resetting.

I don't see why the scope of the lock would need to be enlarged.

	Regards
		Oliver

> To fix this data race, the write operations on line 634-635 
> should be also protected by the lock.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Nacked-by: Oliver Neukum <oneukum@suse.com>

Re: [usb-storage] [PATCH] usb: storage: Fix a possible data race in uas_queuecommand_lck

[Jia-Ju Bai]

On 2018/5/8 16:27, Oliver Neukum wrote:
> Am Dienstag, den 08.05.2018, 15:47 +0800 schrieb Jia-Ju Bai:
>> The write operations to "cmnd->result" and "cmnd->scsi_done"
>> are protected by the lock on line 642-643, but the write operations
>> to these data on line 634-635 are not protected by the lock.
>> Thus, there may exist a data race for "cmnd->result"
>> and "cmnd->scsi_done".
> No,
>
> the write operations need no lock. The low level driver at this point
> owns the command. We cannot race with abort() for a command within
> queuecommand(). We take the lock where we take it to protect
> dev->resetting.
>
> I don't see why the scope of the lock would need to be enlarged.

Okay, thanks for your reply and explanation.


Best wishes,
Jia-Ju Bai