selinux: extended permissions for ioctls

Add extended permissions logic to selinux. Extended permissions
provides additional permissions in 256 bit increments. Extend the
generic ioctl permission check to use the extended permissions for
per-command filtering. Source/target/class sets including the ioctl
permission may additionally include a set of commands. Example:

allowxperm <source> <target>:<class> ioctl unpriv_app_socket_cmds
auditallowxperm <source> <target>:<class> ioctl priv_gpu_cmds

Where unpriv_app_socket_cmds and priv_gpu_cmds are macros
representing commonly granted sets of ioctl commands.

When ioctl commands are omitted only the permissions are checked.
This feature is intended to provide finer granularity for the ioctl
permission that may be too imprecise. For example, the same driver
may use ioctls to provide important and benign functionality such as
driver version or socket type as well as dangerous capabilities such
as debugging features, read/write/execute to physical memory or
access to sensitive data. Per-command filtering provides a mechanism
to reduce the attack surface of the kernel, and limit applications
to the subset of commands required.

The format of the policy binary has been modified to include ioctl
commands, and the policy version number has been incremented to
POLICYDB_VERSION_XPERMS_IOCTL=30 to account for the format
change.

The extended permissions logic is deliberately generic to allow
components to be reused e.g. netlink filters

Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Acked-by: Nick Kralevich <nnk@google.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

2 files changed, 36 insertions, 2 deletions

diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h
index ddf8eec03f21..db12ff14277b 100644
--- a/security/selinux/include/avc.h
+++ b/security/selinux/include/avc.h
@@ -142,6 +142,7 @@ static inline int avc_audit(u32 ssid, u32 tsid,
 }
 
 #define AVC_STRICT 1 /* Ignore permissive mode. */
+#define AVC_EXTENDED_PERMS 2	/* update extended permissions */
 int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 			 u16 tclass, u32 requested,
 			 unsigned flags,
@@ -151,6 +152,10 @@ int avc_has_perm(u32 ssid, u32 tsid,
 		 u16 tclass, u32 requested,
 		 struct common_audit_data *auditdata);
 
+int avc_has_extended_perms(u32 ssid, u32 tsid, u16 tclass, u32 requested,
+		u8 driver, u8 perm, struct common_audit_data *ad);
+
+
 u32 avc_policy_seqno(void);
 
 #define AVC_CALLBACK_GRANT		1
@@ -161,6 +166,7 @@ u32 avc_policy_seqno(void);
 #define AVC_CALLBACK_AUDITALLOW_DISABLE	32
 #define AVC_CALLBACK_AUDITDENY_ENABLE	64
 #define AVC_CALLBACK_AUDITDENY_DISABLE	128
+#define AVC_CALLBACK_ADD_XPERMS		256
 
 int avc_add_callback(int (*callback)(u32 event), u32 events);
 
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 36993ad1c067..6a681d26bf20 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -35,13 +35,14 @@
 #define POLICYDB_VERSION_NEW_OBJECT_DEFAULTS	27
 #define POLICYDB_VERSION_DEFAULT_TYPE	28
 #define POLICYDB_VERSION_CONSTRAINT_NAMES	29
+#define POLICYDB_VERSION_XPERMS_IOCTL	30
 
 /* Range of policy versions we understand*/
 #define POLICYDB_VERSION_MIN   POLICYDB_VERSION_BASE
 #ifdef CONFIG_SECURITY_SELINUX_POLICYDB_VERSION_MAX
 #define POLICYDB_VERSION_MAX	CONFIG_SECURITY_SELINUX_POLICYDB_VERSION_MAX_VALUE
 #else
-#define POLICYDB_VERSION_MAX	POLICYDB_VERSION_CONSTRAINT_NAMES
+#define POLICYDB_VERSION_MAX	POLICYDB_VERSION_XPERMS_IOCTL
 #endif
 
 /* Mask for just the mount related flags */
@@ -109,11 +110,38 @@ struct av_decision {
 	u32 flags;
 };
 
+#define XPERMS_ALLOWED 1
+#define XPERMS_AUDITALLOW 2
+#define XPERMS_DONTAUDIT 4
+
+#define security_xperm_set(perms, x) (perms[x >> 5] |= 1 << (x & 0x1f))
+#define security_xperm_test(perms, x) (1 & (perms[x >> 5] >> (x & 0x1f)))
+struct extended_perms_data {
+	u32 p[8];
+};
+
+struct extended_perms_decision {
+	u8 used;
+	u8 driver;
+	struct extended_perms_data *allowed;
+	struct extended_perms_data *auditallow;
+	struct extended_perms_data *dontaudit;
+};
+
+struct extended_perms {
+	u16 len;	/* length associated decision chain */
+	struct extended_perms_data drivers; /* flag drivers that are used */
+};
+
 /* definitions of av_decision.flags */
 #define AVD_FLAGS_PERMISSIVE	0x0001
 
 void security_compute_av(u32 ssid, u32 tsid,
-			 u16 tclass, struct av_decision *avd);
+			 u16 tclass, struct av_decision *avd,
+			 struct extended_perms *xperms);
+
+void security_compute_xperms_decision(u32 ssid, u32 tsid, u16 tclass,
+			 u8 driver, struct extended_perms_decision *xpermd);
 
 void security_compute_av_user(u32 ssid, u32 tsid,
 			     u16 tclass, struct av_decision *avd);