RDMA/uverbs: Propagate errors from rdma_lookup_get_uobject()

[ Upstream commit 81f8f7454ad9e0bf95efdec6542afdc9a6ab1e24 ]

Currently, the IB uverbs API calls uobj_get_uobj_read(), which in turn
uses the rdma_lookup_get_uobject() helper to retrieve user objects.
In case of failure, uobj_get_uobj_read() returns NULL, overriding the
error code from rdma_lookup_get_uobject(). The IB uverbs API then
translates this NULL to -EINVAL, masking the actual error and
complicating debugging. For example, applications calling ibv_modify_qp
that fails with EBUSY when retrieving the QP uobject will see the
overridden error code EINVAL instead, masking the actual error.

Furthermore, based on rdma-core commit:
"2a22f1ced5f3 ("Merge pull request #1568 from jakemoroni/master")"
Kernel's IB uverbs return values are either ignored and passed on as is
to application or overridden with other errnos in a few cases.

Thus, to improve error reporting and debuggability, propagate the
original error from rdma_lookup_get_uobject() instead of replacing it
with EINVAL.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Link: https://patch.msgid.link/64f9d3711b183984e939962c2f83383904f97dfb.1740577869.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

include/rdma/uverbs_std_types.h

@@ -34,7 +34,7 @@
 static inline void *_uobj_get_obj_read(struct ib_uobject *uobj)
 {
 	if (IS_ERR(uobj))
-		return NULL;
+		return ERR_CAST(uobj);
 	return uobj->object;
 }
 #define uobj_get_obj_read(_object, _type, _id, _attrs)                         \