[PATCH rdma-next v3 6/7] RDMA/irdma: Fix legacy i40iw compat check in create_qp

[Jacob Moroni <jmoroni@google.com>]

The irdma driver maintains backward compatibility with the
legacy i40iw userspace provider by checking the length of
the user response buffer in irdma_create_qp.

Previously, the check relied on udata->outlen < sizeof(uresp).
That is technically okay since there have only ever been two
sizes for the resp struct (legacy and current). However, it
would be a problem if the resp struct is ever expanded in
the future because it would end up triggering the legacy
fallback path for non-legacy irdma providers that just  haven't
moved over to the newer expanded struct yet.

Fix this by explicitly checking for the exact legacy resp size.

Signed-off-by: Jacob Moroni <jmoroni@google.com>
---
 drivers/infiniband/hw/irdma/verbs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/irdma/verbs.c b/drivers/infiniband/hw/irdma/verbs.c
index 00a648922c7b..d8374f7afa87 100644
--- a/drivers/infiniband/hw/irdma/verbs.c
+++ b/drivers/infiniband/hw/irdma/verbs.c
@@ -1139,8 +1139,12 @@ static int irdma_create_qp(struct ib_qp *ibqp,
 	init_completion(&iwqp->free_qp);
 
 	if (udata) {
-		/* GEN_1 legacy support with libi40iw does not have expanded uresp struct */
-		if (udata->outlen < sizeof(uresp)) {
+		/* GEN_1 legacy support with libi40iw does not have expanded
+		 * uresp struct. Check for the exact legacy size (20 bytes) to
+		 * ensure that newer expanded uresp structs don't accidentally
+		 * trigger the legacy fallback.
+		 */
+		if (udata->outlen == IRDMA_CREATE_QP_MIN_RESP_LEN) {
 			uresp.lsmm = 1;
 			uresp.push_idx = IRDMA_INVALID_PUSH_PAGE_INDEX_GEN_1;
 		} else {
-- 
2.55.0.rc0.799.gd6f94ed593-goog