[PATCH v2 2/2] scsi: core: remove command size deduction from scsi_setup_scsi_cmnd

[Tadeusz Struk <tadeusz.struk@linaro.org>]

No need to deduce command size in scsi_setup_scsi_cmnd() anymore
as appropriate checks have been added to scsi_fill_sghdr_rq() function
and the cmd_len should never be zero here.
The code to do that wasn't correct anyway, as it used uninitialized
cmd->cmnd, which caused a null-ptr-deref if the command size was zero
as in the trace below. Fix this by removing the unneeded code.

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 1822 Comm: repro Not tainted 5.15.0 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
Call Trace:
 blk_mq_dispatch_rq_list+0x7c7/0x12d0
 __blk_mq_sched_dispatch_requests+0x244/0x380
 blk_mq_sched_dispatch_requests+0xf0/0x160
 __blk_mq_run_hw_queue+0xe8/0x160
 __blk_mq_delay_run_hw_queue+0x252/0x5d0
 blk_mq_run_hw_queue+0x1dd/0x3b0
 blk_mq_sched_insert_request+0x1ff/0x3e0
 blk_execute_rq_nowait+0x173/0x1e0
 blk_execute_rq+0x15c/0x540
 sg_io+0x97c/0x1370
 scsi_ioctl+0xe16/0x28e0
 sd_ioctl+0x134/0x170
 blkdev_ioctl+0x362/0x6e0
 block_ioctl+0xb0/0xf0
 vfs_ioctl+0xa7/0xf0
 do_syscall_64+0x3d/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xae
---[ end trace 8b086e334adef6d2 ]---
Kernel panic - not syncing: Fatal exception

Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: <linux-scsi@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 5.15, 5.14, 5.10
Fixes: 2ceda20f0a99a74a82b78870f3b3e5fa93087a7f
Reported-by: syzbot+5516b30f5401d4dcbcae@syzkaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
---
Changes in v2:
- prune trace dump according to feedback
---
 drivers/scsi/scsi_lib.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 572673873ddf..e026da7549be 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1174,8 +1174,6 @@ static blk_status_t scsi_setup_scsi_cmnd(struct scsi_device *sdev,
 	}
 
 	cmd->cmd_len = scsi_req(req)->cmd_len;
-	if (cmd->cmd_len == 0)
-		cmd->cmd_len = scsi_command_size(cmd->cmnd);
 	cmd->cmnd = scsi_req(req)->cmd;
 	cmd->transfersize = blk_rq_bytes(req);
 	cmd->allowed = scsi_req(req)->retries;
-- 
2.33.1