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From: "Sugar, David" <dsugar@tresys.com>
To: "selinux-refpolicy@vger.kernel.org"  <selinux-refpolicy@vger.kernel.org>
Subject: Re: [PATCH] Allow systemd to getattr configfile
Date: Wed, 4 Dec 2019 17:22:55 +0000
Message-ID: <e3d4c752-899f-5454-37f5-851378426e8a@tresys.com> (raw)
In-Reply-To: <20191204165614.GA1321684@brutus.lan>



On 12/4/19 11:56 AM, Dominick Grift wrote:
> On Wed, Dec 04, 2019 at 04:33:20PM +0000, Sugar, David wrote:
>> Systemd has ConditionalPathExists which is used to check if a path exists to control starting a service.  But this requires getattr permissions on the file.  This is generally for configuration files.  We are mostly seeing this is in our own policy.  But this lvm denial also fits the example.
>>
>> type=AVC msg=audit(1575427946.229:1624): avc:  denied  { getattr } for  pid=1 comm="systemd" path="/etc/lvm/lvm.conf" dev="dm-0" ino=51799 scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:lvm_etc_t:s0 tclass=file permissive=0
>>
>> This second example is from chronyd, but it is happening becuase I added the conditional in a drop-in file. Note that chronyd_conf_t is already a 'configfile'.
>>
>> type=AVC msg=audit(1575427959.882:1901): avc:  denied  { getattr } for  pid=1 comm="systemd" path="/etc/chrony.conf" dev="dm-0" ino=53824 scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:chronyd_conf_t:s0 tclass=file permissive=1
> 
> how about something a little more general?
> 
> systemd_ConditionPath(`,'
> 	allow init_t $1:dir search_dir_perms;
> 	allow init_t $1:lnk_file read_lnk_file_perms;
> 	allow init_t $1:fifo_file getattr_fifo_file_perms;
> 	allow init_t $1:sock_file getattr_sock_file_perms;
> 	allow init_t $1:file getattr_file_perms;
> 	allow init_t $1:blk_file getattr_blk_file_perms;
> 	allow init_t $1:chr_file getattr_chr_file_perms;
> ')
> 
I think you are suggesting an interface 'systemd_conditionpath' that 
would exist in init.if and then need to be used by any module that wants 
to grant access to a particular type to getattr?

So, for this case, I would need to modify chronyd.te and lvm.te to use 
this interface?

I think you are also suggesting that ConditionPathExists usage in a unit 
file could be trying to check for the existence of something other than 
a configuration file.

Taking it to the extreme, a unit file could be checking for the 
existence of a file that is in a different SELinux domain.  Does it 
instead make sense to use the 'files_getattr_all_files', 
'files_getattr_all_sockets', 'files_getattr_all_pipes', etc... in init.te?


>>
>> Signed-off-by: Dave Sugar <dsugar@tresys.com>
>> ---
>>   policy/modules/kernel/files.if | 20 ++++++++++++++++++++
>>   policy/modules/system/init.te  |  1 +
>>   policy/modules/system/lvm.te   |  2 +-
>>   3 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/policy/modules/kernel/files.if b/policy/modules/kernel/files.if
>> index f1c94411..87be07ae 100644
>> --- a/policy/modules/kernel/files.if
>> +++ b/policy/modules/kernel/files.if
>> @@ -1562,6 +1562,26 @@ interface(`files_relabel_config_dirs',`
>>   	relabel_dirs_pattern($1, configfile, configfile)
>>   ')
>>   
>> +########################################
>> +## <summary>
>> +##	Getattr config files in /etc.
>> +## </summary>
>> +## <param name="domain">
>> +##	<summary>
>> +##	Domain allowed access.
>> +##	</summary>
>> +## </param>
>> +#
>> +interface(`files_getattr_config_files',`
>> +	gen_require(`
>> +		attribute configfile;
>> +	')
>> +
>> +	allow $1 configfile:dir list_dir_perms;
>> +	getattr_files_pattern($1, configfile, configfile)
>> +	read_lnk_files_pattern($1, configfile, configfile)
>> +')
>> +
>>   ########################################
>>   ## <summary>
>>   ##	Read config files in /etc.
>> diff --git a/policy/modules/system/init.te b/policy/modules/system/init.te
>> index 8973a622..747b696e 100644
>> --- a/policy/modules/system/init.te
>> +++ b/policy/modules/system/init.te
>> @@ -320,6 +320,7 @@ ifdef(`init_systemd',`
>>   	domain_subj_id_change_exemption(init_t)
>>   	domain_role_change_exemption(init_t)
>>   
>> +	files_getattr_config_files(init_t)
>>   	files_read_all_pids(init_t)
>>   	files_list_usr(init_t)
>>   	files_list_var(init_t)
>> diff --git a/policy/modules/system/lvm.te b/policy/modules/system/lvm.te
>> index ad4eb579..c05344e0 100644
>> --- a/policy/modules/system/lvm.te
>> +++ b/policy/modules/system/lvm.te
>> @@ -25,7 +25,7 @@ domain_obj_id_change_exemption(lvm_t)
>>   role system_r types lvm_t;
>>   
>>   type lvm_etc_t;
>> -files_type(lvm_etc_t)
>> +files_config_file(lvm_etc_t)
>>   
>>   type lvm_lock_t;
>>   files_lock_file(lvm_lock_t)
>> -- 
>> 2.21.0
>>
> 

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-04 16:33 [PATCH] Allow syslog to write to the runtime socket Sugar, David
2019-12-04 16:33 ` [PATCH] Allow systemd to getattr configfile Sugar, David
2019-12-04 16:56   ` Dominick Grift
2019-12-04 17:22     ` Sugar, David [this message]
2019-12-04 17:31       ` Dominick Grift
2019-12-04 17:43       ` Dominick Grift
2019-12-05  7:46         ` Dominick Grift
2019-12-05 13:19           ` Sugar, David

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