linux-kernel - Re: [PATCH] lib/syscall: Clear return values when no stack

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Message-ID: <CALCETrUvGao=VbUXP9iZuTL9ExAJiU0e8SjMTQTS3x-OYNBcSw@mail.gmail.com>
Date:   Thu, 23 Mar 2017 16:03:42 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Robert Święcki <robert@...ecki.net>,
        Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/syscall: Clear return values when no stack

On Thu, Mar 23, 2017 at 3:46 PM, Kees Cook <keescook@...omium.org> wrote:
> Commit aa1f1a639621 ("lib/syscall: Pin the task stack in collect_syscall()")
> added logic to handle a process stack not existing, but left sp and pc
> uninitialized, which can be later reported via /proc/$pid/syscall for zombie
> processes, potentially exposing kernel memory to userspace.
>
> Zombie /proc/$pid/syscall before:
> -1 0xffffffff9a060100 0xffff92f42d6ad900
>
> Zombie /proc/$pid/syscall after:
> -1 0x0 0x0
>
> Reported-by: Robert Święcki <robert@...ecki.net>
> Fixes: aa1f1a639621 ("lib/syscall: Pin the task stack in collect_syscall()")
> Cc: stable@...r.kernel.org # v4.9+
> Signed-off-by: Kees Cook <keescook@...omium.org>

Whoops!

Reviewed-by: Andy Lutomirski <luto@...nel.org>