linux-kernel - Re: [PATCH] coredump: clarify "unsafe core

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Date:   Sat, 29 Oct 2016 09:00:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] coredump: clarify "unsafe core_pattern" warning

On Sat, Oct 29, 2016 at 8:21 AM, Alexey Dobriyan <adobriyan@...il.com> wrote:
> I was amused to find "unsafe core_pattern" warning having these lines
> in /etc/sysctl.conf:
>
>         fs.suid_dumpable=2
>         kernel.core_pattern=/core/core-%e-%p-%E
>         kernel.core_uses_pid=0
>
> Turns out kernel is formally right. Default core_pattern is just "core",
> which doesn't qualify for secure path while setting suid.dumpable.
>
> Hint admins about solution, clarify sysctl names, delete unnecessary '\'
> characters (string literals are concatenated regardless) and reformat
> for easier grepping.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>

Ah, yes, order of operations mattered. :) I like the rephrasing, thanks!

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>
>  kernel/sysctl.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> commit ba93b14a4f61e4563134abab5d81bb8b53c60df9
> Author: Alexey Dobriyan <adobriyan@...il.com>
> Date:   Sat Oct 29 18:13:57 2016 +0300
>
>     kernel.core_dump
>
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2403,9 +2403,11 @@ static void validate_coredump_safety(void)
>  #ifdef CONFIG_COREDUMP
>         if (suid_dumpable == SUID_DUMP_ROOT &&
>             core_pattern[0] != '/' && core_pattern[0] != '|') {
> -               printk(KERN_WARNING "Unsafe core_pattern used with "\
> -                       "suid_dumpable=2. Pipe handler or fully qualified "\
> -                       "core dump path required.\n");
> +               printk(KERN_WARNING
> +"Unsafe core_pattern used with fs.suid_dumpable=2.\n"
> +"Pipe handler or fully qualified core dump path required.\n"
> +"Set kernel.core_pattern before fs.suid_dumpable.\n"
> +               );
>         }
>  #endif
>  }



-- 
Kees Cook
Nexus Security