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ksmbd: prevent share root removal through empty paths

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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: 74d7970feb ("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>
This commit is contained in:
Namjae Jeon 2026-10-23 08:53:57 +09:00
parent 7220980b24
commit 9fd1fcbbf8
1 changed files with 4 additions and 0 deletions
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4
fs/smb/server/vfs.c
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@ -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 {