# Re: \[kernel-hardening\] \[RFC PATCH 1/2\] security, capabilities: create CAP\_TRUSTED - List: linux-api - 1 message, 1 author - Page: https://ratatoskr.run/linux-api/2017/10/13329685/t ## Re: \[kernel-hardening\] \[RFC PATCH 1/2\] security, capabilities: create CAP\_TRUSTED - From: \ - Date: 2017-10-21 19:04:48 - Message: https://ratatoskr.run/linux-api/2017/10/13329685.md ```text [ref],linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,linux-f2fs-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,jfs-discussion-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,ocfs2-devel-N0ozoZBvEnrZJqsBc5GL+g@public.gmane.org,linux-unionfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,reiserfs-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,selinux-+05T5uksL2qpZYMLLGbcSA@public.gmane.org,linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org From: Nicolas Belouin Message-ID: [ref] On October 21, 2017 7:25:21 PM GMT+02:00, Casey Schaufler [ref] 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 >> --- >> 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 ```