linux-kernel - Re: [PATCH] syslog: check cap_syslog when dmesg

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Message-ID: <4D0232F7.6000105@redhat.com>
Date:	Fri, 10 Dec 2010 09:02:31 -0500
From:	Daniel J Walsh <dwalsh@...hat.com>
To:	James Morris <jmorris@...ei.org>
CC:	"Serge E. Hallyn" <serge@...lyn.com>,
	Eric Paris <eparis@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Kees Cook <kees.cook@...onical.com>,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] syslog: check cap_syslog when dmesg_restrict

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On 12/08/2010 05:56 PM, James Morris wrote:
> On Wed, 8 Dec 2010, Serge E. Hallyn wrote:
> 
>> Eric Paris pointed out that it doesn't make sense to require
>> both CAP_SYS_ADMIN and CAP_SYSLOG for certain syslog actions.
>> So require CAP_SYSLOG, not CAP_SYS_ADMIN, when dmesg_restrict
>> is set.
>>
>> (I'm also consolidating the now common error path)
>>
>> Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
> 
> Applied.
> 
> (Please cc the lsm list with security patches).
> 
>> ---
>>  Documentation/sysctl/kernel.txt |    2 +-
>>  kernel/printk.c                 |   20 ++++++++++----------
>>  2 files changed, 11 insertions(+), 11 deletions(-)
>>
>> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
>> index 209e158..5740671 100644
>> --- a/Documentation/sysctl/kernel.txt
>> +++ b/Documentation/sysctl/kernel.txt
>> @@ -219,7 +219,7 @@ dmesg_restrict:
>>  This toggle indicates whether unprivileged users are prevented from using
>>  dmesg(8) to view messages from the kernel's log buffer.  When
>>  dmesg_restrict is set to (0) there are no restrictions.  When
>> -dmesg_restrict is set set to (1), users must have CAP_SYS_ADMIN to use
>> +dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
>>  dmesg(8).
>>  
>>  The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the default
>> diff --git a/kernel/printk.c b/kernel/printk.c
>> index 0712380..0cecba0 100644
>> --- a/kernel/printk.c
>> +++ b/kernel/printk.c
>> @@ -279,18 +279,12 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
>>  	 * at open time.
>>  	 */
>>  	if (type == SYSLOG_ACTION_OPEN || !from_file) {
>> -		if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
>> -			return -EPERM;
>> +		if (dmesg_restrict && !capable(CAP_SYSLOG))
>> +			goto warn; /* switch to return -EPERM after 2.6.39 */
>>  		if ((type != SYSLOG_ACTION_READ_ALL &&
>>  		     type != SYSLOG_ACTION_SIZE_BUFFER) &&
>> -		    !capable(CAP_SYSLOG)) {
>> -			/* remove after 2.6.38 */
>> -			if (capable(CAP_SYS_ADMIN))
>> -				WARN_ONCE(1, "Attempt to access syslog with "
>> -				  "CAP_SYS_ADMIN but no CAP_SYSLOG "
>> -				  "(deprecated and denied).\n");
>> -			return -EPERM;
>> -		}
>> +		    !capable(CAP_SYSLOG))
>> +			goto warn; /* switch to return -EPERM after 2.6.39 */
>>  	}
>>  
>>  	error = security_syslog(type);
>> @@ -434,6 +428,12 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
>>  	}
>>  out:
>>  	return error;
>> +warn:
>> +	/* remove after 2.6.39 */
>> +	if (capable(CAP_SYS_ADMIN))
>> +		WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
>> +		  "but no CAP_SYSLOG (deprecated and denied).\n");
>> +	return -EPERM;
>>  }
>>  
>>  SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
>> -- 
>> 1.7.0.4
>>
> 

Does anyone have an idea of which domains are going to be effected by
this change?
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