[PATCH 2/3] p9auth: add CAP_GRANT_ID to authorize use of /dev/caphash

["Serge E. Hallyn" <serue@us.ibm.com>]

Granting userid capabilities to another task is a dangerous
privilege.  Don't just let file permissions authorize it.
Define CAP_GRANT_ID as a new capability needed to write to
/dev/caphash.

For one thing this lets us start a factotum server early on
in init, then have init drop CAP_GRANT_ID from its bounding
set so the rest of the system cannot regain it.

(This patch is only useful if the next patch, introducing p9auth fs, is
upstreamed)

TODO - patch for capabilities.7 manpage

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Andrew Morgan <morgan@kernel.org>
Cc: James Morris <jmorris@namei.org>
Cc: linux-security-module@vger.kernel.org
---
 include/linux/capability.h          |    6 +++++-
 security/selinux/include/classmap.h |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 39e5ff5..ba2cbfe 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -355,7 +355,11 @@ struct cpu_vfs_cap_data {
 
 #define CAP_MAC_ADMIN        33
 
-#define CAP_LAST_CAP         CAP_MAC_ADMIN
+/* Allow granting setuid capabilities through p9auth /dev/caphash */
+
+#define CAP_GRANT_ID         34
+
+#define CAP_LAST_CAP         CAP_GRANT_ID
 
 #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 8b32e95..f0ec53a 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -142,7 +142,7 @@ struct security_class_mapping secclass_map[] = {
 	    "node_bind", "name_connect", NULL } },
 	{ "memprotect", { "mmap_zero", NULL } },
 	{ "peer", { "recv", NULL } },
-	{ "capability2", { "mac_override", "mac_admin", NULL } },
+	{ "capability2", { "mac_override", "mac_admin", "grant_id", NULL } },
 	{ "kernel_service", { "use_as_override", "create_files_as", NULL } },
 	{ "tun_socket",
 	  { COMMON_SOCK_PERMS, NULL } },
-- 
1.7.0.4