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

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Date:   Mon, 18 Dec 2017 15:17:32 -0800
From:   Laura Abbott <labbott@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        David Howells <dhowells@...hat.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        regressions@...mhuis.info, Martin Pitt <mpitt@...hat.com>
Subject: Coredump regression with e37fdb785a5f ("exec: Use secureexec for
 setting dumpability")

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@...omium.org>
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@...hat.com>
     Signed-off-by: Kees Cook <keescook@...omium.org>
     Acked-by: Serge Hallyn <serge@...lyn.com>
     Reviewed-by: James Morris <james.l.morris@...cle.com>


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

Thanks,
Laura