[PATCH] scsi: scsi_dh_alua: Fix possible null-ptr-deref

[YueHaibing]

If alloc_workqueue fails in alua_init, it should return
-ENOMEM, otherwise it will trigger null-ptr-deref while
unloading module which calls destroy_workqueue dereference
wq->lock like this:

BUG: KASAN: null-ptr-deref in __lock_acquire+0x6b4/0x1ee0
Read of size 8 at addr 0000000000000080 by task syz-executor.0/7045

CPU: 0 PID: 7045 Comm: syz-executor.0 Tainted: G         C        5.1.0+ #28
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1
Call Trace:
 dump_stack+0xa9/0x10e
 __kasan_report+0x171/0x18d
 ? __lock_acquire+0x6b4/0x1ee0
 kasan_report+0xe/0x20
 __lock_acquire+0x6b4/0x1ee0
 lock_acquire+0xb4/0x1b0
 __mutex_lock+0xd8/0xb90
 drain_workqueue+0x25/0x290
 destroy_workqueue+0x1f/0x3f0
 __x64_sys_delete_module+0x244/0x330
 do_syscall_64+0x72/0x2a0
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes: 03197b61c5ec ("scsi_dh_alua: Use workqueue for RTPG")
Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
---
 drivers/scsi/device_handler/scsi_dh_alua.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index d7ac498ba35a..2a9dcb8973b7 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -1174,10 +1174,8 @@ static int __init alua_init(void)
 	int r;
 
 	kaluad_wq = alloc_workqueue("kaluad", WQ_MEM_RECLAIM, 0);
-	if (!kaluad_wq) {
-		/* Temporary failure, bypass */
-		return SCSI_DH_DEV_TEMP_BUSY;
-	}
+	if (!kaluad_wq)
+		return -ENOMEM;
 
 	r = scsi_register_device_handler(&alua_dh);
 	if (r != 0) {
-- 
2.17.1