Vigil@nce - Linux kernel: read-write access via MNT_DETACH
August 2015 by Vigil@nce
This bulletin was written by Vigil@nce : http://vigilance.fr/offer
SYNTHESIS OF THE VULNERABILITY
A local attacker can bypass access restrictions via MNT_DETACH on
the Linux kernel, in order to read or alter files, bypassing a
User Namespace.
Impacted products: Linux
Severity: 2/4
Creation date: 04/06/2015
DESCRIPTION OF THE VULNERABILITY
The User Namespace (CONFIG_USER_NS) feature provides jailed
environments.
When the user calls umount(MNT_DETACH), the __detach_mounts()
function of the fs/namespace.c file calls umount_tree() which does
not always disconnect the mount point on the file system.
A local attacker can therefore bypass access restrictions via
MNT_DETACH on the Linux kernel, in order to read or alter files,
bypassing a User Namespace.
ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN
http://vigilance.fr/vulnerability/Linux-kernel-read-write-access-via-MNT-DETACH-17068