Coredump regression with e37fdb785a5f ("exec: Use secureexec for setting dumpability")

[Laura Abbott]

Hi,

Fedora got a bug report https://bugzilla.redhat.com/show_bug.cgi?id=1525974
of coredumps failing for systemd units. If systemd units segfault, no
core is produced.

commit e37fdb785a5f95ecadf43b773c97f676500ac7b8 (refs/bisect/bad)
Author: Kees Cook <keescook@xxxxxxxxxxxx>
Date:   Tue Jul 18 15:25:31 2017 -0700

    exec: Use secureexec for setting dumpability
    
    The examination of "current" to decide dumpability is wrong. This was a
    check of and euid/uid (or egid/gid) mismatch in the existing process,
    not the newly created one. This appears to stretch back into even the
    "history.git" tree. Luckily, dumpability is later set in commit_creds().
    In earlier kernel versions before creds existed, similar checks also
    existed late in the exec flow, covering up the mistake as far back as I
    could find.
    
    Note that because the commit_creds() check examines differences of euid,
    uid, egid, gid, and capabilities between the old and new creds, it would
    look like the setup_new_exec() dumpability test could be entirely removed.
    However, the secureexec test may cover a different set of tests (specific
    to the LSMs) than what commit_creds() checks for. So, fix this test to
    use secureexec (the removed euid tests are redundant to the commoncap
    secureexec checks now).
    
    Cc: David Howells <dhowells@xxxxxxxxxx>
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
    Reviewed-by: James Morris <james.l.morris@xxxxxxxxxx>


This was still broken as of -rc3 although interestingly enough this worked
on my rawhide system. Any ideas?

Thanks,
Laura