getpwuid fails silently when run as root inside of mlockall()

(intrepid)root@gorgon:/tmp# ./bad
getpwuid: Success

Inside an intrepid chroot it fails as under jaunty. this implies some kind of kernel issue? raising mlock limits doesn't seem to affect it.

Strangely... *lowering* the ulimit fixes it!

$ ulimit -l 32
$ sudo ./bad
[root]

Er, no. Not any more. No idea what changed.

This appears to be a recently introduced kernel bug; I get the root user returned correctly on 2.6.28-6.17, but I can reproduce the error on 2.6.28-7.20.

smb found:
http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-jaunty.git;a=commit;h=0e42bda2d00f39a6b44b7feae376785fff2affad

This out to be fixed in 2.6.28-8.21: 'mm: fix error case in mlock downgrade reversion'

Appears to me this was a kernel bug. Invalidating the glibc task. Feel free to add back, if I'm misreading the thread, though.

To work around this issue, I added a little hack into eCryptfs to do the mlockall() slightly later (just after the getpwent call). This should be safe to revert now. Assigning to Wesley.

This bug was fixed in the package ecryptfs-utils - 99-0ubuntu1

---------------
ecryptfs-utils (99-0ubuntu1) quantal; urgency=low

  [ Dustin Kirkland ]
  * debian/ecryptfs-utils.postinst: LP: #936093
    - ensure desktop file is executable
  * precise

  [ Wesley Wiedenmeier ]
  * src/utils/mount.ecryptfs.c: LP: #329264
    - remove old hack, that worked around a temporary kernel regression;
      ensure that all mount memory is mlocked

  [ Sebastian Krahmer ]
  * src/pam_ecryptfs/pam_ecryptfs.c: LP: #732614
    - drop group privileges in the same places that user privileges are
      dropped
    - check return status of setresuid() calls and return if they fail
    - drop privileges before checking for the existence of
      ~/.ecryptfs/auto-mount to prevent possible file existence leakage
      by a symlink to a path that typically would not be searchable by
      the user
    - drop privileges before reading salt from the rc file to prevent the
      leakage of root's salt and, more importantly, using the incorrect salt
    - discovered, independently, by Vasiliy Kulikov and Sebastian Krahmer
  * src/pam_ecryptfs/pam_ecryptfs.c: LP: #1020904
    - after dropping privileges, clear the environment before executing the
      private eCryptfs mount helper
    - discovered by Sebastian Krahmer
  * src/utils/mount.ecryptfs_private.c: LP: #1020904
    - do not allow private eCryptfs mount aliases to contain ".." characters
      as a preventative measure against a crafted file path being used as an
      alias
    - force the MS_NOSUID mount flag to protect against user controlled lower
      filesystems, such as an auto mounted USB drive, that may contain a
      setuid-root binary
      + CVE-2012-3409
    - force the MS_NODEV mount flag
    - after dropping privileges, clear the environment before executing umount
    - discovered by Sebastian Krahmer

  [ Tyler Hicks ]
  * src/libecryptfs/key_management.c: LP: #732614
    - zero statically declared buffers to prevent the leakage of stack
      contents in the case of a short file read
    - discovered by Vasiliy Kulikov
  * src/libecryptfs/module_mgr.c, src/pam_ecryptfs/pam_ecryptfs.c:
    - fix compiler warnings
 -- Dustin Kirkland <email address hidden> Fri, 13 Jul 2012 09:52:36 -0500