ceph: Annotate struct ceph_osd_request with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct ceph_osd_request.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Ilya Dryomov <[email protected]>
Cc: Xiubo Li <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: [email protected]
Reviewed-by: "Gustavo A. R. Silva" <[email protected]>
Reviewed-by: Xiubo Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>

Author: kees

include/linux/ceph/osd_client.h

@@ -278,7 +278,7 @@ struct ceph_osd_request {
 	int r_attempts;
 	u32 r_map_dne_bound;
 
-	struct ceph_osd_req_op r_ops[];
+	struct ceph_osd_req_op r_ops[] __counted_by(r_num_ops);
 };
 
 struct ceph_request_redirect {