From 9fd1fcbbf84986a7bcf601a2b90540899069d263 Mon Sep 17 00:00:00 2001 From: Namjae Jeon Date: Fri, 23 Oct 2026 08:53:57 +0900 Subject: [PATCH] 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) Signed-off-by: Namjae Jeon --- fs/smb/server/vfs.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c index 5360c6999bb3..4ee72eda9bc0 100644 --- a/fs/smb/server/vfs.c +++ b/fs/smb/server/vfs.c @@ -62,6 +62,10 @@ static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf, struct dentry *d; if (pathname[0] == '\0') { + /* The share root must never be removed. */ + if (for_remove) + return -EINVAL; + pathname = share_conf->path; root_share_path = NULL; } else {