io_uring/query: prevent infinite loops

If the query chain forms a cycle, the interface will loop indefinitely.
Make sure it handles fatal signals, so the user can kill the process and
hence break out of the infinite loop.

Fixes: c265ae75f9 ("io_uring: introduce io_uring querying")
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/query.c

@@ -88,6 +88,10 @@ int io_query(struct io_ring_ctx *ctx, void __user *arg, unsigned nr_args)
 		if (ret)
 			return ret;
 		uhdr = u64_to_user_ptr(next_hdr);
+
+		if (fatal_signal_pending(current))
+			return -EINTR;
+		cond_resched();
 	}
 	return 0;
 }