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Date: Thu, 22 Dec 2022 08:36:39 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: oss-security@...ts.openwall.com
Subject: Re: [Linux] /proc/pid/stat parsing bugs
On Wed, 21 Dec 2022 at 19:25, Yann Droneaud <ydroneaud@...eya.com> wrote:
>
> Hi,
>
> 21 décembre 2022 à 18:59 "Demi Marie Obenour" <demi@...isiblethingslab.com> a écrit:
> > On Wed, Dec 21, 2022 at 06:13:17PM +0100, Dmitry Vyukov wrote:
> >
> > >
> > > Hello,
> > >
> > > This is not a single vulnerability, the list of affected software is
> > > large, but it's not a security issue for all of it.
> > >
> > > It occurred to me that most of the Linux procfs /proc/pid/stat and
> > > /proc/pid/task/tid/stat parsing code out there is buggy. The fine
> > > contains a set of numbers about the task:
> > > https://man7.org/linux/man-pages/man5/proc.5.html
> > >
> > > e.g. $ cat /proc/self/stat
> > > 1715376 (cat) R 1544883 1715376 1544883 34819 1715376 4194304 106 0 0
> > > 0 0 0 0 0 20 0 1 0 42505561 9207808 237 18446744073709551615
> > > 93955355631616 93955355651497 140737444557056 0 0 0 0 0 0 0 0 0 17 36
> > > 0 0 0 0 0 93955355667504 93955355669120 93955385581568 140737444559745
> > > 140737444559765 140737444559765 140737444564971 0
> > >
> > > Most of the code splits it by space and takes an N-th field.
> > > The problem is that the process name "(cat)" can contain spaces (and
> > > brackets). Potentially some important software (containers/sandboxes)
> > > can be tricked into getting wrong data, and I've seen cases close to
> > > stack overflows (buffer for a fixed number of fields is allocated on
> > > stack).
> > >
> > > Some examples:
> > > OpenJDK:
> > > https://sourcegraph.com/github.com/openjdk/jdk/-/blob/src/jdk.management/unix/native/libmanagement_ext/OperatingSystemImpl.c?L133-139
> > > https://sourcegraph.com/github.com/openjdk/jdk8u/-/blob/jdk/src/solaris/native/sun/management/OperatingSystemImpl.c?L223-229
> > >
> > > Ansible:
> > > https://sourcegraph.com/github.com/ansible/ansible/-/blob/lib/ansible/modules/yum.py?L507-510
> > >
> > > Libuv:
> > > https://sourcegraph.com/github.com/libuv/libuv/-/blob/src/unix/linux.c?L674-701
> > >
> > > bdwgc:
> > > https://sourcegraph.com/github.com/mono/linux-packaging-mono/-/blob/external/bdwgc/os_dep.c?L1138-1155
> > >
> > > But really most of the code that does it:
> > > https://sourcegraph.com/search?q=context:global+/%5C%22%5C/proc%5C/.*%5C/stat%5C%22/
> > >
> > > The only way to parse it is to do strrchr(')') first (fortunately it
> > > contains just one unescaped string).
> > >
> > > Thanks
> > >
> >
> > Should Linux be patched to somehow escape the spaces, or replace them
> > with something else? /proc/pid/status is even harder to parse robustly.
>
> It might be difficult because of Linux's policy to not break userspace ABI.
>
> For example, I've suggested some sort of escaping on /proc/net/unix, and
> it was not welcomed.
>
> https://lore.kernel.org/all/20220406102213.2020784-1-ydroneaud@opteya.com/
>
> In a follow up, I've added a PoC for injecting fake entries in /proc/net/unix
>
> https://lore.kernel.org/all/8a87957e-4d33-9351-ae74-243441cb03cd@opteya.com/
>
> I didn't found a way to abuse this issue: no vulnerability, no need for
> a change that would break userspace ABI.
Somebody filed a Debian bug to fix the kernel:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1024811
(kernel docs claim the name can be parsed with %s, but it can't)
> Regards.
>
> --
> Yann Droneaud
> OPTEYA
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