Managing Permissions for AppArmor Files in the /sys File System

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Environment

SUSE Linux Enterprise Server 15 all Service Packs
SUSE Linux Enterprise Server 12 all Service Packs

Situation

After changing the permissions of the following files to 664, they revert to 666 upon system reboot:

/sys/kernel/security/apparmor/.remove
/sys/kernel/security/apparmor/.replace
/sys/kernel/security/apparmor/.load
/sys/kernel/security/apparmor/.access

Resolution

The affected files are managed by AppArmor. Their permissions are set to 666 upon creation, making permanent modifications challenging. This behavior is hard-coded in the kernel source, meaning changes require kernel source modifications, however, modifying the kernel source is not supported by SUSE.

Cause

The /sys file system is a virtual or pseudo file system, which differs from the general Linux file system. Permissions visible through the ls command are not necessarily enforced. The kernel performs additional permission checks when files are accessed or modified, for example, even if permissions appear to be 666, certain operations may still fail due to kernel-enforced restrictions.

Additional Information

Reference: Linux Kernel Source Code
https://github.com/torvalds/linux/blob/master/security/apparmor/apparmorfs.c#L2670

https://github.com/torvalds/linux/blob/master/security/apparmor/apparmorfs.c#L489

Disclaimer

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