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.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 5.0 | 5.0.x |
| linux / linux_kernel | 5.3 | 5.3.x |
| canonical / ubuntu_linux | 18.04 | 18.04.x |
| canonical / ubuntu_linux | 19.04 | 19.04.x |