linux-kernel - [PATCH 0/5] Refactor kallsyms_show

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Message-Id: <20200702232638.2946421-1-keescook@chromium.org>
Date:   Thu,  2 Jul 2020 16:26:33 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dominik Czarnota <dominik.czarnota@...ilofbits.com>
Cc:     Kees Cook <keescook@...omium.org>, Jessica Yu <jeyu@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Will Deacon <will@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matteo Croce <mcroce@...hat.com>,
        Edward Cree <ecree@...arflare.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Alexander Lobakin <alobakin@...nk.ru>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/5] Refactor kallsyms_show_value() users for correct cred

Hi,

I'm not sure who should carry this tree (me? Greg? akpm? Linus?), but
it fixes a kernel address exposure bug reported by Dominik Czarnota,
where /sys/modules/*/sections/* contents were visible to uid-0 without
CAP_SYSLOG (e.g. in containers):

This is correct, with CAP_SYSLOG:
 # cat /sys/module/*/sections/.*text
 0xffffffffc0458000
 ...

This is broken:
 # capsh --drop=CAP_SYSLOG -- -c "cat /sys/module/*/sections/.*text"
 0xffffffffc0458000
 ...

Fixing this required refactoring of several internals, and in the process
uncovered other users of kallsyms_show_value() that were doing checks
during "read" context instead of "open" context. This fixes all of these
cases by plumbing the file->f_cred through to their ultimate checks via
kallsyms_show_value()'s new cred argument.

Testing, reviews, and acks appreciated. :)

Thanks!

-Kees


Kees Cook (5):
  kallsyms: Refactor kallsyms_show_value() to take cred
  module: Refactor section attr into bin attribute
  module: Do not expose section addresses to non-CAP_SYSLOG
  kprobes: Do not expose probe addresses to non-CAP_SYSLOG
  bpf: Check correct cred for CAP_SYSLOG in bpf_dump_raw_ok()

 include/linux/filter.h     |  4 +--
 include/linux/kallsyms.h   |  5 ++--
 kernel/bpf/syscall.c       | 37 +++++++++++++++------------
 kernel/kallsyms.c          | 17 ++++++++-----
 kernel/kprobes.c           |  4 +--
 kernel/module.c            | 51 ++++++++++++++++++++------------------
 net/core/sysctl_net_core.c |  2 +-
 7 files changed, 67 insertions(+), 53 deletions(-)

-- 
2.25.1