IB/iser: Fix possible NULL deref at iser_inv_desc()

In case target remote invalidates bogus rkey and signature is not used,
pi_ctx is NULL deref.

The commit also fails the connection on bogus remote invalidation.

Fixes: 59caaed ("IB/iser: Support the remote invalidation exception")
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/iser/iser_initiator.c

@@ -589,13 +589,19 @@ void iser_login_rsp(struct ib_cq *cq, struct ib_wc *wc)
 	ib_conn->post_recv_buf_count--;
 }
 
-static inline void
+static inline int
 iser_inv_desc(struct iser_fr_desc *desc, u32 rkey)
 {
-	if (likely(rkey == desc->rsc.mr->rkey))
+	if (likely(rkey == desc->rsc.mr->rkey)) {
 		desc->rsc.mr_valid = 0;
-	else if (likely(rkey == desc->pi_ctx->sig_mr->rkey))
+	} else if (likely(desc->pi_ctx && rkey == desc->pi_ctx->sig_mr->rkey)) {
 		desc->pi_ctx->sig_mr_valid = 0;
+	} else {
+		iser_err("Bogus remote invalidation for rkey %#x\n", rkey);
+		return -EINVAL;
+	}
+
+	return 0;
 }
 
 static int
@@ -623,12 +629,14 @@ iser_check_remote_inv(struct iser_conn *iser_conn,
 
 			if (iser_task->dir[ISER_DIR_IN]) {
 				desc = iser_task->rdma_reg[ISER_DIR_IN].mem_h;
-				iser_inv_desc(desc, rkey);
+				if (unlikely(iser_inv_desc(desc, rkey)))
+					return -EINVAL;
 			}
 
 			if (iser_task->dir[ISER_DIR_OUT]) {
 				desc = iser_task->rdma_reg[ISER_DIR_OUT].mem_h;
-				iser_inv_desc(desc, rkey);
+				if (unlikely(iser_inv_desc(desc, rkey)))
+					return -EINVAL;
 			}
 		} else {
 			iser_err("failed to get task for itt=%d\n", hdr->itt);