CVE-2019-15793

In shiftfs, a non-upstream patch to the Linux kernel included in the Ubuntu
5.0 and 5.3 kernel series, several locations which shift ids translate
user/group ids before performing operations in the lower filesystem were
translating them into init_user_ns, whereas they should have been
translated into the s_user_ns for the lower filesystem. This resulted in
using ids other than the intended ones in the lower fs, which likely did
not map into the shifts s_user_ns. A local attacker could use this to
possibly bypass discretionary access control permissions.

Bugs

• <https://bugs.launchpad.net/bugs/1850867&gt;