linux-kernel - Re: [PATCH/RFC] cap_syslog: make CAP_SYS_ADMIN deprecation notice less alarming

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Date:	Thu, 4 Aug 2011 04:39:05 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Jonathan Nieder <jrnieder@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Gergely Nagy <algernon@...abit.hu>, david@...g.hm,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Marc Koschewski <marc@...nowledge.org>,
	lkml <linux-kernel@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Nick Bowler <nbowler@...iptictech.com>
Subject: Re: [PATCH/RFC] cap_syslog: make CAP_SYS_ADMIN deprecation notice
 less alarming

Quoting Jonathan Nieder (jrnieder@...il.com):
> syslog-ng versions in active use assume that CAP_SYS_ADMIN is
> sufficent to access syslog.  As a result, ever since CAP_SYSLOG was
> introduce in v2.6.38-rc1~429^2~18 (security: Define CAP_SYSLOG,
> 2010-11-25), they have triggered a warning, complete with kernel
> backtrace.
> 
> v2.6.38-rc5~46 (cap_syslog: accept CAP_SYS_ADMIN for now, 2011-02-10)
> made things a little better by removing the regression in behavior,
> just keeping the WARN_ONCE.  But still, this is a warning that adds
> many lines to syslog, sets a taint flag, and alarms sysadmins when

Sets the taint flag?  That's a bit over the top, so:

> nothing worse has happened than use of an old userspace with a recent
> kernel.
> 
> Convert the WARN_ONCE to a printk_once to avoid this while continuing
> to give userspace developers a hint that this is an unwanted
> backward-compatibility feature and won't be around forever.
> 
> Reported-by: Ralf Hildebrandt <ralf.hildebrandt@...rite.de>
> Reported-by: Niels <zorglub_olsen@...mail.com>
> Reported-by: Paweł Sikora <pluto@...k.net>
> Liked-by: Gergely Nagy <algernon@...house-project.org>
> Signed-off-by: Jonathan Nieder <jrnieder@...il.com>

Acked-by: Serge Hallyn <serge@...lyn.com>

thanks,
-serge

> ---
> Hi,
> 
> Nothing urgent about this, but it seems to be a frequently[1] reported[2]
> source of unnecessary worry.  Thoughts?
> 
> [1] http://thread.gmane.org/gmane.linux.kernel/1145040
> [2] http://thread.gmane.org/gmane.linux.kernel/1153808
> 
> Context: http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=32;bug=636501
> 
>  kernel/printk.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 37dff342..db64c951 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -318,7 +318,8 @@ static int check_syslog_permissions(int type, bool from_file)
>  			return 0;
>  		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
>  		if (capable(CAP_SYS_ADMIN)) {
> -			WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
> +			printk_once(KERN_WARNING
> +				 "Attempt to access syslog with CAP_SYS_ADMIN "
>  				 "but no CAP_SYSLOG (deprecated).\n");
>  			return 0;
>  		}
> -- 
> 1.7.6
> 
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