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

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Message-ID: <ZZgfCZKho2Dsv7VM@alley>
Date: Fri, 5 Jan 2024 16:23:53 +0100
From: Petr Mladek <pmladek@...e.com>
To: Theodore Ts'o <tytso@....edu>
Cc: Jingzi Meng <mengjingzi@....ac.cn>, gregkh@...uxfoundation.org,
	gpiccoli@...lia.com, john.ogness@...utronix.de,
	keescook@...omium.org, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	senozhatsky@...omium.org, tony.luck@...el.com
Subject: Re: [PATCH] cap_syslog: remove CAP_SYS_ADMIN when dmesg_restrict

On Fri 2024-01-05 09:49:44, Theodore Ts'o wrote:
> 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.
> 
> What testing have you done to make sure that this is OK?  "May have
> had enough time"?  That's not very reassuring?
> 
> Also, note that we can't actually reuse the bit position of
> CAP_SYS_ADMIN since it's likely that there may be pre-existing
> capability masks that are still using that position.  So there isn't
> all that much upside in trying to retire CAP_SYS_ADMIN --- if you as a
> system administrator think it's not too course, then just don't use
> it.
> 
> It's unclear to me what goal you have in trying to mess with the
> capability definitions?  Perhaps it might be useful if you were to
> explicitly state your goals in these proposals?

My understanding is that this patch is about reducing overlap of
capabilities.

Allowing the same thing with more capabilities seems to go against
the idea of separate capabilities.

Kernel has printed the warning for 13 years. It is a long
time to fix configuration for newly installed systems. And I doubt
that anyone is installing a new kernel on 13 year's old system.

IMHO, this fits into the category that it should be OK until
anyone complains. But I might miss something.

Best Regards,
Petr