linux-kernel - Re: [PATCH] cap_syslog: remove CAP_SYS_ADMIN when dmesg

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Message-ID: <202401080956.7FBE02F54C@keescook>
Date: Mon, 8 Jan 2024 09:57:55 -0800
From: Kees Cook <keescook@...omium.org>
To: Jingzi Meng <mengjingzi@....ac.cn>
Cc: gregkh@...uxfoundation.org, gpiccoli@...lia.com,
	john.ogness@...utronix.de, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org, pmladek@...e.com, rostedt@...dmis.org,
	senozhatsky@...omium.org, tony.luck@...el.com
Subject: Re: [PATCH] cap_syslog: remove CAP_SYS_ADMIN when dmesg_restrict

On Fri, Jan 05, 2024 at 02:20:07PM +0800, Jingzi Meng wrote:
> CAP_SYSLOG was separated from CAP_SYS_ADMIN and introduced in Linux
> 2.6.37 (2010-11). For a long time, certain syslog actions required
> CAP_SYS_ADMIN or CAP_SYSLOG. Maybe it’s time to officially remove
> CAP_SYS_ADMIN for more fine-grained control.
> 
> CAP_SYS_ADMIN was once removed but added back for backwards
> compatibility reasons. In commit 38ef4c2e437d ("syslog: check cap_syslog
> when dmesg_restrict") (2010-12), CAP_SYS_ADMIN was no longer needed. And
> in commit ee24aebffb75 ("cap_syslog: accept CAP_SYS_ADMIN for now")
> (2011-02), it was accepted again. Since then, CAP_SYS_ADMIN has been
> preserved.
> 
> Now that almost 13 years have passed, the legacy application may have
> had enough time to be updated.

I can't find anything mention this warning in recent times except this:
https://sysdig.com/blog/container-escape-capabilities-falco-detection/
which is mainly an example about how to apply Capabilities, not a
software failure.

> Signed-off-by: Jingzi Meng <mengjingzi@....ac.cn>

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

If you can boot a few stock modern distros and verify nothing emits this
warning any more should be sufficient evidence that this can be dropped.

-Kees

-- 
Kees Cook