Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns
What we want is to verify there is that clone won’t expose something hidden by a mount we wouldn’t be able to undo. “Wouldn’t be able to undo” may be a result of MNT_LOCKED on a child, but it may also come from lacking admin rights in the userns of the namespace mount belongs to.
clone_private_mnt() checks the former, but not the latter.
There’s a number of rather confusing CAP_SYS_ADMIN checks in various userns during the mount, especially with the new mount API; they serve different purposes and in case of clone_private_mnt() they usually, but not always end up covering the missing check mentioned above.
Details
- Affected product:
- AlmaLinux 9.2 ESU , Oracle Linux 7 ELS , TuxCare 9.6 ESU , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS , Ubuntu 20.04 ELS
- Affected packages:
- kernel @ 5.14.0 (+6 more)
In the Linux kernel, the following vulnerability has been resolved:
clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns
What we want is to verify there is that clone won’t expose something hidden by a mount we wouldn’t be able to undo. “Wouldn’t be able to undo” may be a result of MNT_LOCKED on a child, but it may also come from lacking admin rights in the userns of the namespace mount belongs to.
clone_private_mnt() checks the former, but not the latter.
There’s a number of rather confusing CAP_SYS_ADMIN checks in various userns during the mount, especially with the new mount API; they serve different purposes and in case of clone_private_mnt() they usually, but not always end up covering the missing check mentioned above.