linux-kernel - [PATCH RFC 0/4] coredump: mitigate privilege escalation of process coredump

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20211227223436.317091-1-wander@redhat.com>
Date:   Mon, 27 Dec 2021 19:34:31 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Laurent Vivier <laurent@...ier.eu>,
        YunQiang Su <ysu@...ecomp.com>, Helge Deller <deller@....de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Rafael Aquini <aquini@...hat.com>,
        Phil Auld <pauld@...hat.com>, Rolf Eike Beer <eb@...ix.com>,
        Muchun Song <songmuchun@...edance.com>,
        linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and
        infrastructure)), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH RFC 0/4] coredump: mitigate privilege escalation of process coredump

A set-uid executable might be a vector to privilege escalation if the
system configures the coredump file name pattern as a relative
directory destiny. The full description of the vulnerability and
a demonstration of how we can exploit it can be found at [1].

This patch series adds a PF_SUID flag to the process in execve if it is
set-[ug]id binary and elevates the new image's privileges.

In the do_coredump function, we check if:

1) We have the SUID_FLAG set
2) We have CAP_SYS_ADMIN (the process might have decreased its
   privileges)
3) The current directory is owned by root (the current code already
   checks for core_pattern being a relative path).
4) non-privileged users don't have permission to write to the current
   directory.

If all four conditions match, we set the need_suid_safe flag.

An alternative implementation (and more elegant IMO) would be saving
the fsuid and fsgid of the process in the task_struct before loading the
new image to the memory. But this approach would add eight bytes to all
task_struct instances where only a tiny fraction of the processes need
it and under a configuration that not all (most?) distributions don't
adopt by default.

Wander Lairson Costa (4):
  exec: add a flag indicating if an exec file is a suid/sgid
  process: add the PF_SUID flag
  coredump: mitigate privilege escalation of process coredump
  exec: only set the suid flag if the current proc isn't root

 fs/coredump.c           | 15 +++++++++++++++
 fs/exec.c               | 10 ++++++++++
 include/linux/binfmts.h |  6 +++++-
 include/linux/sched.h   |  1 +
 kernel/fork.c           |  2 ++
 5 files changed, 33 insertions(+), 1 deletion(-)

-- 
2.27.0