UBUNTU-CVE-2026-93282: High severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix maximum allowed access checks The DACL permission check looks for an ACE matching the current user and falls back to the Everyone ACE. It does not consider an Authenticated Users ACE, even though an authenticated session is a member of that well-known group. As a result, opening a file whose access is granted through S-1-5-11 can incorrectly fail with STATUSACCESSDENIED. Treat an Authenticated Users ACE as a fallback entry alongside Everyone. The maximal access calculation also combines access masks from every ACE, regardless of whether its SID applies to the current user. This can grant rights belonging to an unrelated principal. Process only ACEs applying to the user, Everyone, or Authenticated Users, and accumulate allowed and denied masks in ACL order. Preserve explicitly requested access bits so they are validated against the resulting maximal mask. When ACCESSSYSTEMSECURITY is denied, report STATUSPRIVILEGENOTHELD instead of the generic STATUSACCESSDENIED. Access to the system ACL requires a security privilege that ksmbd does not grant. For regular files, include FILEEXECUTE in maximal access when the client requested GENERICEXECUTE and the DACL grants the complete file-read set. Keep a direct FILEEXECUTE request subject to the explicit DACL bit. This matches the POSIX file ACL mapping without broadening specific execute requests. Do not replace rights from an applicable NT ACE with a POSIX ACL entry. The POSIX ACL is only a fallback when no user, Everyone, or Authenticated Users ACE applies; otherwise it can incorrectly broaden the stored DACL. This fixes smb2.maximumallowed.maximumallowed.