FilesystemCapabilties

Dumping ground for notes on supporting filesystem capabilities.

Open Questions

  • Filesystems without xattr support (NFS, squashfs, etc). Possible solutions:
    • VFS 'xattr_backing_file' mount option
    • union mount with xattr-capable ext3 over xattr-challenged NFS
    • stackable FS
    • Wait for fs's to support xattrs Smile :)

  • Determine possible caps needed for programs. Perhaps:
    • walk compiled assembly, listing caps
      • definately needed (i.e. cap_sys_admin for mount)
      • possibly needed (i.e. cap_dac_override)
    • audit?
    • kprobe
    • wrap application in MAC (eg. apparmor) policy and put it in allowed auditing (apparmor complain mode) and collect list of capabilities used.
  • library to wrap syscalls to enable caps
    • tries syscall(SYS_xyz), if fail with -EPERM/EACCESS, then
    • oldcaps = enable_eff_cap_by_syscall(SYS_xyz)
      • looks through library of (syscall->caps_list) pairs

      • copies any x in caps_list which is in pP to pE
      • retries SYS_xyz
      • resets oldcaps

Blockers

Good

  • "cp -a" works

Bad

  • NFS does not support xattr

Ugly

  • libcap2's pam_cap has unexpected parsing results (should allow multiple matches on user)

Fixed

  • libcap2-bin does not install pam_cap.so into the common-auth stack automatically (LP: #534658).

Security/FilesystemCapabilties (last edited 2011-09-27 18:44:25 by jjohansen)