Leaking Path in XFS's ioctl interface(missing LSM check)
From: Alan Cox <hidden>
Date: 2018-09-26 18:24:41
Also in:
linux-xfs, lkml
On Wed, 26 Sep 2018 11:33:29 +1000 Dave Chinner [off-list ref] wrote:
On Tue, Sep 25, 2018 at 08:51:50PM -0400, TongZhang wrote:quoted
Hi, I'm bringing up this issue again to let of LSM developers know the situation, and would like to know your thoughts. Several weeks ago I sent an email to the security list to discuss the issue where XFS's ioctl interface can do things like vfs_readlink without asking LSM's permission, which we think is kind of weird and this kind of operation should be audited by LSM.These aren't user interfaces. They are filesystem maintenance and extension interfaces. They are intended for low level filesystem utilities that require complete, unrestricted access to the underlying filesystem via holding CAP_SYSADMIN in the initns.
CAP_SYS_ADMIN is meaningless in an environment using a strong LSM set up. So what if I have CAP_SYS_ADMIN ? In a secure environment low level complete unrestricted access to the file system is most definitely something that should be mediated. CAP_SYS_ADMIN is also a bit weird because low level access usually implies you can bypass access controls so you should also check CAP_SYS_DAC ? Alan