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From: Nicolas Belouin <nicolas@xxxxxxxxxx>
Message-ID: <E5A1BDA4-A309-4118-84D5-72780F619EBA@xxxxxxxxxx>
On October 21, 2017 7:25:21 PM GMT+02:00, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>On 10/21/2017 6:45 AM, Nicolas Belouin wrote:
>> with CAP_SYS_ADMIN being bloated, the usefulness of using it to
>> flag a process to be entrusted for e.g reading and writing trusted
>> xattr is near zero.
>> CAP_TRUSTED aims to provide userland with a way to mark a process as
>> entrusted to do specific (not specially admin-centered) actions. It
>> would for example allow a process to red/write the trusted xattrs.
>
>Please explain how this is different from CAP_MAC_ADMIN in
>any existing use case. If it is significantly different, how
>would the two interact?
>From my point of view, CAP_MAC_ADMIN allows one to read/write security xattrs, those are meant to describe security policies. As far as I know of, trusted xattrs are intended for a privileged process to read or write arbitrary data. I don't have any real world example in mind that use trusted xattrs, but I'll try to find one.
>
>> Signed-off-by: Nicolas Belouin <nicolas@xxxxxxxxxx>
>> ---
>> include/uapi/linux/capability.h | 6 +++++-
>> security/selinux/include/classmap.h | 5 +++--
>> 2 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/uapi/linux/capability.h
>b/include/uapi/linux/capability.h
>> index ce230aa6d928..27e457b93c84 100644
>> --- a/include/uapi/linux/capability.h
>> +++ b/include/uapi/linux/capability.h
>> @@ -369,7 +369,11 @@ struct vfs_ns_cap_data {
>>
>> #define CAP_SYS_MOUNT 38
>>
>> -#define CAP_LAST_CAP CAP_SYS_MOUNT
>> +/* Allow read/write trusted xattr */
>> +
>> +#define CAP_TRUSTED 39
>> +
>> +#define CAP_LAST_CAP CAP_TRUSTED
>>
>> #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
>>
>> diff --git a/security/selinux/include/classmap.h
>b/security/selinux/include/classmap.h
>> index a873dce97fd5..f5dc8e109f5a 100644
>> --- a/security/selinux/include/classmap.h
>> +++ b/security/selinux/include/classmap.h
>> @@ -24,9 +24,10 @@
>> "audit_control", "setfcap"
>>
>> #define COMMON_CAP2_PERMS "mac_override", "mac_admin", "syslog", \
>> - "wake_alarm", "block_suspend", "audit_read", "sys_mount"
>> + "wake_alarm", "block_suspend", "audit_read", "sys_mount", \
>> + "trusted"
>>
>> -#if CAP_LAST_CAP > CAP_SYS_MOUNT
>> +#if CAP_LAST_CAP > CAP_TRUSTED
>> #error New capability defined, please update COMMON_CAP2_PERMS.
>> #endif
>>
Nicolas
