io_uring: refactor io_uring_allowed()

Have io_uring_allowed() return an error code directly instead of
true/false. This is needed for follow-up work to guard io_uring_setup()
with LSM.

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
[PM: goto-to-return conversion as discussed on-list]
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: effective-light

io_uring/io_uring.c

@@ -3791,29 +3791,35 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params)
 	return io_uring_create(entries, &p, params);
 }
 
-static inline bool io_uring_allowed(void)
+static inline int io_uring_allowed(void)
 {
 	int disabled = READ_ONCE(sysctl_io_uring_disabled);
 	kgid_t io_uring_group;
 
 	if (disabled == 2)
-		return false;
+		return -EPERM;
 
 	if (disabled == 0 || capable(CAP_SYS_ADMIN))
-		return true;
+		return 0;
 
 	io_uring_group = make_kgid(&init_user_ns, sysctl_io_uring_group);
 	if (!gid_valid(io_uring_group))
-		return false;
+		return -EPERM;
+
+	if (!in_group_p(io_uring_group))
+		return -EPERM;
 
-	return in_group_p(io_uring_group);
+	return 0;
 }
 
 SYSCALL_DEFINE2(io_uring_setup, u32, entries,
 		struct io_uring_params __user *, params)
 {
-	if (!io_uring_allowed())
-		return -EPERM;
+	int ret;
+
+	ret = io_uring_allowed();
+	if (ret)
+		return ret;
 
 	return io_uring_setup(entries, params);
 }