ksmbd: fix path resolution in ksmbd_vfs_kern_path_create

Overview

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.

Affected

• Linux >= 265fd1991c1db85fbabaad4946ca0e63e2ae688d < a2516be69048856e2a49a51e00975dc59431f95c
• Linux >= 265fd1991c1db85fbabaad4946ca0e63e2ae688d < 489d1ded01425c0fb33418172c0e4e588467526b
• Linux >= 265fd1991c1db85fbabaad4946ca0e63e2ae688d < c7c884a1305aa4540eb7942a50bd356b34120e1f
• Linux >= 265fd1991c1db85fbabaad4946ca0e63e2ae688d < 98185b3025beeae92d1fe700d5db26b9ac4bf025
• Linux >= 265fd1991c1db85fbabaad4946ca0e63e2ae688d < 1c8951963d8ed357f70f59e0ad4ddce2199d2016
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.