Re: [PATCH v2] security_syslog() should be called once only

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 30 May 2015 16:51:34 +0300 Vasily Averin <vvs@virtuozzo.com> wrote:

> On 28.05.2015 02:43, Andrew Morton wrote:
> > So we run security_syslog() for actions other than open() (of kmsg). 
> > Why?
> Could you please clarify this question?
> 
> Linux kernel have reasonable default security policy and it's great.
> And at the same time kernel allows to override default behaviour
> and set custom security policy.
> For example, to prohibit work on Saturday.
> QA can use it for random failures generation.
> Why not?

This change:

: --- a/kernel/printk/printk.c~security_syslog-should-be-called-once-only
: +++ a/kernel/printk/printk.c
: @@ -496,11 +496,11 @@ int check_syslog_permissions(int type, b
:  	 * already done the capabilities checks at open time.
:  	 */
:  	if (from_file && type != SYSLOG_ACTION_OPEN)
: -		return 0;
: +		goto ok;
: 
: ...
: 
:  		}
:  		return -EPERM;
:  	}
: +ok:
:  	return security_syslog(type);
:  }


Means that we will now call security_syslog() for SYSLOG_ACTION_CLOSE,
SYSLOG_ACTION_READ, SYSLOG_ACTION_READ_ALL, etc.

That's new behaviour and it may be wrong.  Why should
check_syslog_permissions() call security_syslog() for anything other
than SYSLOG_ACTION_OPEN?