fuse: limit xattr returned size

Don't let userspace filesystem give bogus values for the size of xattr and
xattr list.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/xattr.c

@@ -79,7 +79,7 @@ ssize_t fuse_getxattr(struct inode *inode, const char *name, void *value,
 	}
 	ret = fuse_simple_request(fc, &args);
 	if (!ret && !size)
-		ret = outarg.size;
+		ret = min_t(ssize_t, outarg.size, XATTR_SIZE_MAX);
 	if (ret == -ENOSYS) {
 		fc->no_getxattr = 1;
 		ret = -EOPNOTSUPP;
@@ -138,7 +138,7 @@ ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size)
 	}
 	ret = fuse_simple_request(fc, &args);
 	if (!ret && !size)
-		ret = outarg.size;
+		ret = min_t(ssize_t, outarg.size, XATTR_LIST_MAX);
 	if (ret > 0 && size)
 		ret = fuse_verify_xattr_list(list, ret);
 	if (ret == -ENOSYS) {