Re: [Linux] /proc/pid/stat parsing bugs

[Demi Marie Obenour <demi () invisiblethingslab com>]

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.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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