IB/srp: Fix use-after-free in srp_reset_req()

commit 9b796d06 upstream.

srp_free_req() uses the scsi_cmnd structure contents to unmap
buffers, so we must invoke srp_free_req() before we release
ownership of that structure.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -620,9 +620,9 @@ static void srp_reset_req(struct srp_target_port *target, struct srp_request *re
 	struct scsi_cmnd *scmnd = srp_claim_req(target, req, NULL);
 
 	if (scmnd) {
+		srp_free_req(target, req, scmnd, 0);
 		scmnd->result = DID_RESET << 16;
 		scmnd->scsi_done(scmnd);
-		srp_free_req(target, req, scmnd, 0);
 	}
 }