| Message ID | 20171021134558.21195-1-nicolas@belouin.fr |
|---|---|
| State | Not Applicable |
| Delegated to: | Richard Weinberger |
| Headers | show |
| Series | [RFC,1/2] security, capabilities: create CAP_TRUSTED | expand |
Quoting Nicolas Belouin (nicolas@belouin.fr): > 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. You say "for example". Are you intending to add more uses? If so, what are they? If not, how about renaming it CAP_TRUSTED_XATTR? What all does allowing writes to trusted xattrs give you? There are the overlayfs whiteouts, what else?
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? > Signed-off-by: Nicolas Belouin <nicolas@belouin.fr> > --- > 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 >
<james.l.morris@oracle.com>,linux-ext4@vger.kernel.org,linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net,linux-fsdevel@vger.kernel.org,linux-mtd@lists.infradead.org,jfs-discussion@lists.sourceforge.net,ocfs2-devel@oss.oracle.com,linux-unionfs@vger.kernel.org,reiserfs-devel@vger.kernel.org,linux-security-module@vger.kernel.org,selinux@tycho.nsa.gov,linux-api@vger.kernel.org,kernel-hardening@lists.openwall.com From: Nicolas Belouin <nicolas@belouin.fr> Message-ID: <E5A1BDA4-A309-4118-84D5-72780F619EBA@belouin.fr> On October 21, 2017 7:25:21 PM GMT+02:00, Casey Schaufler <casey@schaufler-ca.com> 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@belouin.fr> >> --- >> 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
<james.l.morris@oracle.com>,linux-ext4@vger.kernel.org,linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net,linux-fsdevel@vger.kernel.org,linux-mtd@lists.infradead.org,jfs-discussion@lists.sourceforge.net,ocfs2-devel@oss.oracle.com,linux-unionfs@vger.kernel.org,reiserfs-devel@vger.kernel.org,linux-security-module@vger.kernel.org,selinux@tycho.nsa.gov,linux-api@vger.kernel.org,kernel-hardening@lists.openwall.com From: Nicolas Belouin <nicolas@belouin.fr> Message-ID: <99179B10-4EAE-4FAB-9D14-B885156261B3@belouin.fr> On October 21, 2017 6:03:02 PM GMT+02:00, "Serge E. Hallyn" <serge@hallyn.com> wrote: >Quoting Nicolas Belouin (nicolas@belouin.fr): >> 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. > >You say "for example". Are you intending to add more uses? If so, >what >are they? If not, how about renaming it CAP_TRUSTED_XATTR? > I don't see any other use for now, but I don't want it to be too narrow and non usable in a similar context in the future. So I believe the underlying purpose of marking a process as "trusted" (even if for now it only means rw permission on trusted xattr) is more meaningful. >What all does allowing writes to trusted xattrs give you? There are >the overlayfs whiteouts, what else? Nicolas
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
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. Signed-off-by: Nicolas Belouin <nicolas@belouin.fr> --- include/uapi/linux/capability.h | 6 +++++- security/selinux/include/classmap.h | 5 +++-- 2 files changed, 8 insertions(+), 3 deletions(-)