selinux: match extended permissions to their base permissions

In commit d1d991efaf34 ("selinux: Add netlink xperm support") a new
extended permission was added ("nlmsg"). This was the second extended
permission implemented in selinux ("ioctl" being the first one).

Extended permissions are associated with a base permission. It was found
that, in the access vector cache (avc), the extended permission did not
keep track of its base permission. This is an issue for a domain that is
using both extended permissions (i.e., a domain calling ioctl() on a
netlink socket). In this case, the extended permissions were
overlapping.

Keep track of the base permission in the cache. A new field "base_perm"
is added to struct extended_perms_decision to make sure that the
extended permission refers to the correct policy permission. A new field
"base_perms" is added to struct extended_perms to quickly decide if
extended permissions apply.

While it is in theory possible to retrieve the base permission from the
access vector, the same base permission may not be mapped to the same
bit for each class (e.g., "nlmsg" is mapped to a different bit for
"netlink_route_socket" and "netlink_audit_socket"). Instead, use a
constant (AVC_EXT_IOCTL or AVC_EXT_NLMSG) provided by the caller.

Fixes: d1d991efaf34 ("selinux: Add netlink xperm support")
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 21 insertions, 7 deletions

diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 3d5c563cfc4c..d9f58b5d0f49 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -582,7 +582,7 @@ static void type_attribute_bounds_av(struct policydb *policydb,
 }
 
 /*
- * Flag which drivers have permissions.
+ * Flag which drivers have permissions and which base permissions are covered.
  */
 void services_compute_xperms_drivers(
 		struct extended_perms *xperms,
@@ -592,12 +592,19 @@ void services_compute_xperms_drivers(
 
 	switch (node->datum.u.xperms->specified) {
 	case AVTAB_XPERMS_IOCTLDRIVER:
+		xperms->base_perms |= AVC_EXT_IOCTL;
 		/* if one or more driver has all permissions allowed */
 		for (i = 0; i < ARRAY_SIZE(xperms->drivers.p); i++)
 			xperms->drivers.p[i] |= node->datum.u.xperms->perms.p[i];
 		break;
 	case AVTAB_XPERMS_IOCTLFUNCTION:
+		xperms->base_perms |= AVC_EXT_IOCTL;
+		/* if allowing permissions within a driver */
+		security_xperm_set(xperms->drivers.p,
+					node->datum.u.xperms->driver);
+		break;
 	case AVTAB_XPERMS_NLMSG:
+		xperms->base_perms |= AVC_EXT_NLMSG;
 		/* if allowing permissions within a driver */
 		security_xperm_set(xperms->drivers.p,
 					node->datum.u.xperms->driver);
@@ -631,8 +638,7 @@ static void context_struct_compute_av(struct policydb *policydb,
 	avd->auditallow = 0;
 	avd->auditdeny = 0xffffffff;
 	if (xperms) {
-		memset(&xperms->drivers, 0, sizeof(xperms->drivers));
-		xperms->len = 0;
+		memset(xperms, 0, sizeof(*xperms));
 	}
 
 	if (unlikely(!tclass || tclass > policydb->p_classes.nprim)) {
@@ -969,13 +975,19 @@ void services_compute_xperms_decision(struct extended_perms_decision *xpermd,
 {
 	switch (node->datum.u.xperms->specified) {
 	case AVTAB_XPERMS_IOCTLFUNCTION:
-	case AVTAB_XPERMS_NLMSG:
-		if (xpermd->driver != node->datum.u.xperms->driver)
+		if (xpermd->base_perm != AVC_EXT_IOCTL ||
+		    xpermd->driver != node->datum.u.xperms->driver)
 			return;
 		break;
 	case AVTAB_XPERMS_IOCTLDRIVER:
-		if (!security_xperm_test(node->datum.u.xperms->perms.p,
-					xpermd->driver))
+		if (xpermd->base_perm != AVC_EXT_IOCTL ||
+		    !security_xperm_test(node->datum.u.xperms->perms.p,
+					 xpermd->driver))
+			return;
+		break;
+	case AVTAB_XPERMS_NLMSG:
+		if (xpermd->base_perm != AVC_EXT_NLMSG ||
+		    xpermd->driver != node->datum.u.xperms->driver)
 			return;
 		break;
 	default:
@@ -1010,6 +1022,7 @@ void security_compute_xperms_decision(u32 ssid,
 				      u32 tsid,
 				      u16 orig_tclass,
 				      u8 driver,
+				      u8 base_perm,
 				      struct extended_perms_decision *xpermd)
 {
 	struct selinux_policy *policy;
@@ -1023,6 +1036,7 @@ void security_compute_xperms_decision(u32 ssid,
 	struct ebitmap_node *snode, *tnode;
 	unsigned int i, j;
 
+	xpermd->base_perm = base_perm;
 	xpermd->driver = driver;
 	xpermd->used = 0;
 	memset(xpermd->allowed->p, 0, sizeof(xpermd->allowed->p));