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>

1 files changed, 32 insertions, 1 deletions

diff --git a/security/selinux/ss/avtab.h b/security/selinux/ss/avtab.h
index adb451cd44f9..d946c9dc3c9c 100644
--- a/security/selinux/ss/avtab.h
+++ b/security/selinux/ss/avtab.h
@@ -23,6 +23,7 @@
 #ifndef _SS_AVTAB_H_
 #define _SS_AVTAB_H_
 
+#include "security.h"
 #include <linux/flex_array.h>
 
 struct avtab_key {
@@ -37,13 +38,43 @@ struct avtab_key {
 #define AVTAB_MEMBER		0x0020
 #define AVTAB_CHANGE		0x0040
 #define AVTAB_TYPE		(AVTAB_TRANSITION | AVTAB_MEMBER | AVTAB_CHANGE)
+/* extended permissions */
+#define AVTAB_XPERMS_ALLOWED	0x0100
+#define AVTAB_XPERMS_AUDITALLOW	0x0200
+#define AVTAB_XPERMS_DONTAUDIT	0x0400
+#define AVTAB_XPERMS		(AVTAB_XPERMS_ALLOWED | \
+				AVTAB_XPERMS_AUDITALLOW | \
+				AVTAB_XPERMS_DONTAUDIT)
 #define AVTAB_ENABLED_OLD   0x80000000 /* reserved for used in cond_avtab */
 #define AVTAB_ENABLED		0x8000 /* reserved for used in cond_avtab */
 	u16 specified;	/* what field is specified */
 };
 
+/*
+ * For operations that require more than the 32 permissions provided by the avc
+ * extended permissions may be used to provide 256 bits of permissions.
+ */
+struct avtab_extended_perms {
+/* These are not flags. All 256 values may be used */
+#define AVTAB_XPERMS_IOCTLFUNCTION	0x01
+#define AVTAB_XPERMS_IOCTLDRIVER	0x02
+	/* extension of the avtab_key specified */
+	u8 specified; /* ioctl, netfilter, ... */
+	/*
+	 * if 256 bits is not adequate as is often the case with ioctls, then
+	 * multiple extended perms may be used and the driver field
+	 * specifies which permissions are included.
+	 */
+	u8 driver;
+	/* 256 bits of permissions */
+	struct extended_perms_data perms;
+};
+
 struct avtab_datum {
-	u32 data; /* access vector or type value */
+	union {
+		u32 data; /* access vector or type value */
+		struct avtab_extended_perms *xperms;
+	} u;
 };
 
 struct avtab_node {