scsi: qla2xxx: Warn if done() or free() are called on an already freed srb

Emit a warning when ->done or ->free are called on an already freed
srb. There is a hidden use-after-free bug in the driver which corrupts
the srb memory pool which originates from the cleanup callbacks.

An extensive search didn't bring any lights on the real problem. The
initial fix was to set both pointers to NULL and try to catch invalid
accesses. But instead the memory corruption was gone and the driver
didn't crash. Since not all calling places check for NULL pointer, add
explicitly default handlers. With this we workaround the memory
corruption and add a debug help.

Link: https://lore.kernel.org/r/20200908081516.8561-2-dwagner@suse.deReviewed-by: Martin Wilck <mwilck@suse.com>
Reviewed-by: Arun Easi <aeasi@marvell.com>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qla2xxx/qla_init.c

@@ -63,6 +63,16 @@ void qla2x00_sp_free(srb_t *sp)
 	qla2x00_rel_sp(sp);
 }
 
+void qla2xxx_rel_done_warning(srb_t *sp, int res)
+{
+	WARN_ONCE(1, "Calling done() of an already freed srb %p object\n", sp);
+}
+
+void qla2xxx_rel_free_warning(srb_t *sp)
+{
+	WARN_ONCE(1, "Calling free() of an already freed srb %p object\n", sp);
+}
+
 /* Asynchronous Login/Logout Routines -------------------------------------- */
 
 unsigned long

drivers/scsi/qla2xxx/qla_inline.h

@@ -207,10 +207,15 @@ qla2xxx_get_qpair_sp(scsi_qla_host_t *vha, struct qla_qpair *qpair,
 	return sp;
 }
 
+void qla2xxx_rel_done_warning(srb_t *sp, int res);
+void qla2xxx_rel_free_warning(srb_t *sp);
+
 static inline void
 qla2xxx_rel_qpair_sp(struct qla_qpair *qpair, srb_t *sp)
 {
 	sp->qpair = NULL;
+	sp->done = qla2xxx_rel_done_warning;
+	sp->free = qla2xxx_rel_free_warning;
 	mempool_free(sp, qpair->srb_mempool);
 	QLA_QPAIR_MARK_NOT_BUSY(qpair);
 }