Re: [PATCH v17 0/4] overlayfs override_creds=off & nested get xattr fix

[Paul Moore]

On Tue, Oct 20, 2020 at 3:17 PM Mark Salyzyn <salyzyn@xxxxxxxxxxx> wrote:
>
> Mark Salyzyn (3):
>   Add flags option to get xattr method paired to __vfs_getxattr
>   overlayfs: handle XATTR_NOSECURITY flag for get xattr method
>   overlayfs: override_creds=off option bypass creator_cred
>
> Mark Salyzyn + John Stultz (1):
>   overlayfs: inode_owner_or_capable called during execv
>
> The first three patches address fundamental security issues that should
> be solved regardless of the override_creds=off feature.
>
> The fourth adds the feature depends on these other fixes.
>
> By default, all access to the upper, lower and work directories is the
> recorded mounter's MAC and DAC credentials.  The incoming accesses are
> checked against the caller's credentials.
>
> If the principles of least privilege are applied for sepolicy, the
> mounter's credentials might not overlap the credentials of the caller's
> when accessing the overlayfs filesystem.  For example, a file that a
> lower DAC privileged caller can execute, is MAC denied to the
> generally higher DAC privileged mounter, to prevent an attack vector.
>
> We add the option to turn off override_creds in the mount options; all
> subsequent operations after mount on the filesystem will be only the
> caller's credentials.  The module boolean parameter and mount option
> override_creds is also added as a presence check for this "feature",
> existence of /sys/module/overlay/parameters/overlay_creds
>
> Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
> Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> To: linux-fsdevel@xxxxxxxxxxxxxxx
> To: linux-unionfs@xxxxxxxxxxxxxxx
> Cc: linux-security-module@xxxxxxxxxxxxxxx
> Cc: kernel-team@xxxxxxxxxxx

The SELinux list should also be CC'd on these patches.  For those who
may just be seeing this, the lore link is below:

https://lore.kernel.org/linux-security-module/20201020191732.4049987-1-salyzyn@xxxxxxxxxxx/T/#t

-- 
paul moore
www.paul-moore.com