scsi: iscsi: Fix iscsi_task use after free

mainline inclusion
from mainline-v5.15-rc5
commit 258aad75
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9R4O4
CVE: CVE-2021-47427

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=258aad75c62146453d03028a44f2f1590d58e1f6

--------------------------------

Commit d39df158 ("scsi: iscsi: Have abort handler get ref to conn")
added iscsi_get_conn()/iscsi_put_conn() calls during abort handling but
then also changed the handling of the case where we detect an already
completed task where we now end up doing a goto to the common put/cleanup
code. This results in a iscsi_task use after free, because the common
cleanup code will do a put on the iscsi_task.

This reverts the goto and moves the iscsi_get_conn() to after we've checked
if the iscsi_task is valid.

Link: https://lore.kernel.org/r/20211004210608.9962-1-michael.christie@oracle.com


Fixes: d39df158 ("scsi: iscsi: Have abort handler get ref to conn")
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Li Nan <linan122@huawei.com>