In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix path resolution in ksmbd_vfs_kern_path_create
The SMB2 open lookup is rooted at the share with LOOKUP_BENEATH, but the
create/mkdir/hardlink sink is not: ksmbd_vfs_kern_path_create() builds an
absolute path with convert_to_unix_name() and resolves it from AT_FDCWD
via start_creating_path(), so a “..” component is walked from the real
filesystem root and escapes the export.
An authenticated client races a missing path component so the rooted open
lookup returns -ENOENT (taking the create branch) while the same component
is present (a directory) when the create walk runs; the create then
resolves “..” out of the share.
Root the create walk at the share like the lookup and rename paths already
are: resolve the parent with vfs_path_parent_lookup(…, LOOKUP_BENEATH,
&share_conf->vfs_path) and create the final component with
start_creating_noperm(). convert_to_unix_name() then has no callers and is
removed.
