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Date: Thu, 30 Nov 2017 13:22:05 +0100
From: Djalal Harouni <tixxdz@...il.com>
To: "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc: Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>, James Morris <james.l.morris@...cle.com>,
Ben Hutchings <ben.hutchings@...ethink.co.uk>, Solar Designer <solar@...nwall.com>,
Serge Hallyn <serge@...lyn.com>, Jessica Yu <jeyu@...nel.org>,
Rusty Russell <rusty@...tcorp.com.au>, linux-kernel <linux-kernel@...r.kernel.org>,
LSM List <linux-security-module@...r.kernel.org>, kernel-hardening@...ts.openwall.com,
Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>,
"David S. Miller" <davem@...emloft.net>, Network Development <netdev@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 next 3/5] modules:capabilities: automatic module
loading restriction
On Thu, Nov 30, 2017 at 2:23 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> On Mon, Nov 27, 2017 at 06:18:36PM +0100, Djalal Harouni wrote:
>> diff --git a/include/linux/module.h b/include/linux/module.h
>> index 5cbb239..c36aed8 100644
>> --- a/include/linux/module.h
>> +++ b/include/linux/module.h
>> @@ -261,7 +261,16 @@ struct notifier_block;
>>
>> #ifdef CONFIG_MODULES
>>
>> -extern int modules_disabled; /* for sysctl */
>> +enum {
>> + MODULES_AUTOLOAD_ALLOWED = 0,
>> + MODULES_AUTOLOAD_PRIVILEGED = 1,
>> + MODULES_AUTOLOAD_DISABLED = 2,
>> +};
>> +
>
> Can you kdocify these and add a respective rst doc file? Maybe stuff your
> extensive docs which you are currently adding to
> Documentation/sysctl/kernel.txt to this new file and in kernel.txt just refer
> to it. This way this can be also nicely visibly documented on the web with the
> new sphinx.
>
> This way you can take advantage of the kdocs you are already adding and refer
> to them.
Alright I'll do it in the next series next week, we'll change the
semantics as requested by Linus and Kees here:
http://www.openwall.com/lists/kernel-hardening/2017/11/29/38
To block the privilege escalation through the usermod helper.
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 2fb4e27..0b6f0c8 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -683,6 +688,15 @@ static struct ctl_table kern_table[] = {
>> .extra1 = &one,
>> .extra2 = &one,
>> },
>> + {
>> + .procname = "modules_autoload_mode",
>> + .data = &modules_autoload_mode,
>> + .maxlen = sizeof(int),
>> + .mode = 0644,
>> + .proc_handler = modules_autoload_dointvec_minmax,
>
> It would seem this is a unint ... so why not reflect that?
>
>> @@ -2499,6 +2513,20 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
>> }
>> #endif
>>
>> +#ifdef CONFIG_MODULES
>> +static int modules_autoload_dointvec_minmax(struct ctl_table *table, int write,
>> + void __user *buffer, size_t *lenp, loff_t *ppos)
>> +{
>> + /*
>> + * Only CAP_SYS_MODULE in init user namespace are allowed to change this
>> + */
>> + if (write && !capable(CAP_SYS_MODULE))
>> + return -EPERM;
>> +
>> + return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
>> +}
>> +#endif
>
> We now have proc_douintvec_minmax().
>
Yes, however in that same response by Linus it was suggested to drop
the sysctl completely, so next iterations will not have this code.
Thank you for the review!
--
tixxdz
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