io_uring: verify resv is 0 in ringfd register/unregister

Only allow resv field to be 0 in struct io_uring_rsrc_update user
arguments.

Fixes: e7a6c00d ("io_uring: add support for registering ring file descriptors")
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220412163042.2788062-4-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -10533,6 +10533,11 @@ static int io_ringfd_register(struct io_ring_ctx *ctx, void __user *__arg,
 			break;
 		}
 
+		if (reg.resv) {
+			ret = -EINVAL;
+			break;
+		}
+
 		if (reg.offset == -1U) {
 			start = 0;
 			end = IO_RINGFD_REG_MAX;
@@ -10579,7 +10584,7 @@ static int io_ringfd_unregister(struct io_ring_ctx *ctx, void __user *__arg,
 			ret = -EFAULT;
 			break;
 		}
-		if (reg.offset >= IO_RINGFD_REG_MAX) {
+		if (reg.resv || reg.offset >= IO_RINGFD_REG_MAX) {
 			ret = -EINVAL;
 			break;
 		}