ksmbd: prevent share root removal through empty paths

A FileLinkInformation request can supply "/" as the new link name.
smb2_get_name() strips the trailing slash and passes an empty string to
ksmbd_vfs_kern_path_start_removing().

ksmbd_vfs_path_lookup() resolves an empty pathname as the configured share
path, without LOOKUP_BENEATH. With ReplaceIfExists set, smb2_create_link()
can therefore remove the share root from its parent before link creation
fails. An authenticated client with a writable share and DELETE access to
a file can trigger this if the share root is empty and the mapped user
has write and search permission on its parent directory.

Return -EINVAL for empty pathnames when for_remove is set, before
resolving the share path or acquiring removal resources. Ordinary lookups
continue to accept empty pathnames for opening the share root.

Fixes: 74d7970febf7 ("ksmbd: fix racy issue from using ->d_parent and ->d_name")
Cc: stable@vger.kernel.org
Reported-by: Zachariah Mithani (AploSec) <zachariah@aplosai.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions