erofs: zero out when listxattr is called with no xattr

BugLink: https://bugs.launchpad.net/bugs/1856869
commit 926d1650176448d7684b991fbe1a5b1a8289e97c upstream.

As David reported [1], ENODATA returns when attempting
to modify files by using EROFS as an overlayfs lower layer.

The root cause is that listxattr could return unexpected
-ENODATA by mistake for inodes without xattr. That breaks
listxattr return value convention and it can cause copy
up failure when used with overlayfs.

Resolve by zeroing out if no xattr is found for listxattr.

[1] https://lore.kernel.org/r/CAEvUa7nxnby+rxK-KRMA46=exeOMApkDMAV08AjMkkPnTPV4CQ@mail.gmail.com
Link: https://lore.kernel.org/r/20191201084040.29275-1-hsiangkao@aol.com
Fixes: cadf1ccf1b00 ("staging: erofs: add error handling for xattr submodule")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/staging/erofs/xattr.c b/drivers/staging/erofs/xattr.c
index df40654b9fbbb7d4a5e46945fcbfe851a1cd04c9..bec68beaeca350052e2d8cefef7a7ca257bd0643 100644 (file)
--- a/drivers/staging/erofs/xattr.c
+++ b/drivers/staging/erofs/xattr.c
@@ -649,6 +649,8 @@ ssize_t erofs_listxattr(struct dentry *dentry,
        struct listxattr_iter it;
 
        ret = init_inode_xattrs(d_inode(dentry));
+       if (ret == -ENOATTR)
+               return 0;
        if (ret)
                return ret;