Ubuntu Wiki

Dumping ground for notes on supporting filesystem capabilities.

Open Questions

• Filesystems without xattr support (NFS, 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

• 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

• "rsync -AXa" works, but "AX" should be part of "a"
• cpio fails
• tar fails

  • http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=254615

  • http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=451932

    • http://old.nabble.com/patches-for-acl%2C-xattrs%2C-and-selinux-support-ts21075155.html

• dpkg-deb does not know about xattrs.

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).