fanotify: call fanotify_events_supported() before path_permission() and security_path_notify()

The latter trigger LSM (e.g. SELinux) checks, which will log a denial
when permission is denied, so it's better to do them after validity
checks to avoid logging a denial when the operation would fail anyway.

Fixes: 0b3b094 ("fanotify: Disallow permission events for proc filesystem")
Signed-off-by: Ondrej Mosnacek <[email protected]>
Reviewed-by: Amir Goldstein <[email protected]>
Reviewed-by: Paul Moore <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jan Kara <[email protected]>

Author: WOnder93

fs/notify/fanotify/fanotify_user.c

@@ -1210,6 +1210,7 @@ static int fanotify_find_path(int dfd, const char __user *filename,
 
 		*path = fd_file(f)->f_path;
 		path_get(path);
+		ret = 0;
 	} else {
 		unsigned int lookup_flags = 0;
 
@@ -1219,22 +1220,7 @@ static int fanotify_find_path(int dfd, const char __user *filename,
 			lookup_flags |= LOOKUP_DIRECTORY;
 
 		ret = user_path_at(dfd, filename, lookup_flags, path);
-		if (ret)
-			goto out;
 	}
-
-	/* you can only watch an inode if you have read permissions on it */
-	ret = path_permission(path, MAY_READ);
-	if (ret) {
-		path_put(path);
-		goto out;
-	}
-
-	ret = security_path_notify(path, mask, obj_type);
-	if (ret)
-		path_put(path);
-
-out:
 	return ret;
 }
 
@@ -2058,6 +2044,15 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 			goto path_put_and_out;
 	}
 
+	/* you can only watch an inode if you have read permissions on it */
+	ret = path_permission(&path, MAY_READ);
+	if (ret)
+		goto path_put_and_out;
+
+	ret = security_path_notify(&path, mask, obj_type);
+	if (ret)
+		goto path_put_and_out;
+
 	if (fid_mode) {
 		ret = fanotify_test_fsid(path.dentry, flags, &__fsid);
 		if (ret)