scsi: dc395x: Fix a missing check on list iterator

The bug is here:

	p->target_id, p->target_lun);

The list iterator 'p' will point to a bogus position containing HEAD if the
list is empty or no element is found. This case must be checked before any
use of the iterator, otherwise it will lead to an invalid memory access.

To fix this bug, add a check. Use a new variable 'iter' as the list
iterator, and use the original variable 'p' as a dedicated pointer to point
to the found element.

Link: https://lore.kernel.org/r/20220414040231.2662-1-xiam0nd.tong@gmail.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/dc395x.c b/drivers/scsi/dc395x.c
index 67a8971..670a836 100644 (file)
--- a/drivers/scsi/dc395x.c
+++ b/drivers/scsi/dc395x.c
@@ -3585,10 +3585,19 @@ static struct DeviceCtlBlk *device_alloc(struct AdapterCtlBlk *acb,
 #endif
        if (dcb->target_lun != 0) {
                /* Copy settings */
-               struct DeviceCtlBlk *p;
-               list_for_each_entry(p, &acb->dcb_list, list)
-                       if (p->target_id == dcb->target_id)
+               struct DeviceCtlBlk *p = NULL, *iter;
+
+               list_for_each_entry(iter, &acb->dcb_list, list)
+                       if (iter->target_id == dcb->target_id) {
+                               p = iter;
                                break;
+                       }
+
+               if (!p) {
+                       kfree(dcb);
+                       return NULL;
+               }
+
                dprintkdbg(DBG_1, 
                       "device_alloc: <%02i-%i> copy from <%02i-%i>\n",
                       dcb->target_id, dcb->target_lun,