Re: [PATCH] sysctl selinux: Don't look at table->de

[ebiederm@xmission.com (Eric W. Biederman)]

Stephen Smalley <sds@tycho.nsa.gov> writes:

> On Sun, 2007-01-28 at 12:21 -0700, Eric W. Biederman wrote:
>> With the sysctl cleanups sysctl is not really a part of proc
>> it just shows up there, and any path based approach will not
>> adequately describe the data as sysctl is essentially a
>> union mount underneath the covers.  As designed this mechanism
>> is viewer dependent so trying to be path based gets even worse.
>> 
>> However the permissions in sys_sysctl are currently immutable
>> and going through proc does not change the permission checks
>> when accessing sysctl.  So we might as well stick with the well
>> defined sysctl sid, as that is what selinux uses when proc is
>> not compiled in.
>> 
>> I.e.  I see no hope for salvaging the selinux_proc_get_sid call
>> in selinux_sysctl so I'm removing it.
>> 
>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
>> ---
>>  security/selinux/hooks.c |    8 ++------
>>  1 files changed, 2 insertions(+), 6 deletions(-)
>> 
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 7b38372..3a36057 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -1438,12 +1438,8 @@ static int selinux_sysctl(ctl_table *table, int op)
>>  
>>  	tsec = current->security;
>>  
>> -	rc = selinux_proc_get_sid(table->de, (op == 001) ?
>> -	                          SECCLASS_DIR : SECCLASS_FILE, &tsid);
>> -	if (rc) {
>> -		/* Default to the well-defined sysctl SID. */
>> -		tsid = SECINITSID_SYSCTL;
>> -	}
>> +	/* Use the well-defined sysctl SID. */
>> +	tsid = SECINITSID_SYSCTL;
>>  
>>  	/* The op values are "defined" in sysctl.c, thereby creating
>>  	 * a bad coupling between this module and sysctl.c */
>
> NAK.  Mapping all sysctls to a single security label prevents any kind
> of fine-grained security on sysctls, and current policies already make
> use of the current distinctions to limit access to particular sets of
> sysctls to particular processes.  As is, I'd expect breakage of current
> systems running SELinux from this patch, because (confined) processes
> that formerly only required access to specific sysctl labels will
> suddenly run into denials on the generic fallback label.

Reasonable.  There is the issue that your code already had this code
path for when /proc was compiled out.

> If the ctl_table supplied more information about the functional purpose
> and the security sensitivity of the sysctl, then we could leverage that
> information instead, as long as we can at least derive the current
> labelings from that information for compatibility.

What do information do you need to do need?  Do you need extra fields in sysctl?
I am more than willing to help but I am not familiar enough with selinux
to do a reasonable job on my own.

Eric