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>

security/selinux/hooks.c

@@ -3216,6 +3216,46 @@ static void selinux_file_free_security(struct file *file)
 	file_free_security(file);
 }
 
+/*
+ * Check whether a task has the ioctl permission and cmd
+ * operation to an inode.
+ */
+int ioctl_has_perm(const struct cred *cred, struct file *file,
+		u32 requested, u16 cmd)
+{
+	struct common_audit_data ad;
+	struct file_security_struct *fsec = file->f_security;
+	struct inode *inode = file_inode(file);
+	struct inode_security_struct *isec = inode->i_security;
+	struct lsm_ioctlop_audit ioctl;
+	u32 ssid = cred_sid(cred);
+	int rc;
+	u8 driver = cmd >> 8;
+	u8 xperm = cmd & 0xff;
+
+	ad.type = LSM_AUDIT_DATA_IOCTL_OP;
+	ad.u.op = &ioctl;
+	ad.u.op->cmd = cmd;
+	ad.u.op->path = file->f_path;
+
+	if (ssid != fsec->sid) {
+		rc = avc_has_perm(ssid, fsec->sid,
+				SECCLASS_FD,
+				FD__USE,
+				&ad);
+		if (rc)
+			goto out;
+	}
+
+	if (unlikely(IS_PRIVATE(inode)))
+		return 0;
+
+	rc = avc_has_extended_perms(ssid, isec->sid, isec->sclass,
+			requested, driver, xperm, &ad);
+out:
+	return rc;
+}
+
 static int selinux_file_ioctl(struct file *file, unsigned int cmd,
 			      unsigned long arg)
 {
@@ -3258,7 +3298,7 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
 	 * to the file's ioctl() function.
 	 */
 	default:
-		error = file_has_perm(cred, file, FILE__IOCTL);
+		error = ioctl_has_perm(cred, file, FILE__IOCTL, (u16) cmd);
 	}
 	return error;
 }

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);
 

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);

security/selinux/ss/avtab.c

@@ -24,6 +24,7 @@
 #include "policydb.h"
 
 static struct kmem_cache *avtab_node_cachep;
+static struct kmem_cache *avtab_xperms_cachep;
 
 /* Based on MurmurHash3, written by Austin Appleby and placed in the
  * public domain.
@@ -70,11 +71,24 @@ avtab_insert_node(struct avtab *h, int hvalue,
 		  struct avtab_key *key, struct avtab_datum *datum)
 {
 	struct avtab_node *newnode;
+	struct avtab_extended_perms *xperms;
 	newnode = kmem_cache_zalloc(avtab_node_cachep, GFP_KERNEL);
 	if (newnode == NULL)
 		return NULL;
 	newnode->key = *key;
-	newnode->datum = *datum;
+
+	if (key->specified & AVTAB_XPERMS) {
+		xperms = kmem_cache_zalloc(avtab_xperms_cachep, GFP_KERNEL);
+		if (xperms == NULL) {
+			kmem_cache_free(avtab_node_cachep, newnode);
+			return NULL;
+		}
+		*xperms = *(datum->u.xperms);
+		newnode->datum.u.xperms = xperms;
+	} else {
+		newnode->datum.u.data = datum->u.data;
+	}
+
 	if (prev) {
 		newnode->next = prev->next;
 		prev->next = newnode;
@@ -107,8 +121,12 @@ static int avtab_insert(struct avtab *h, struct avtab_key *key, struct avtab_dat
 		if (key->source_type == cur->key.source_type &&
 		    key->target_type == cur->key.target_type &&
 		    key->target_class == cur->key.target_class &&
-		    (specified & cur->key.specified))
+		    (specified & cur->key.specified)) {
+			/* extended perms may not be unique */
+			if (specified & AVTAB_XPERMS)
+				break;
 			return -EEXIST;
+		}
 		if (key->source_type < cur->key.source_type)
 			break;
 		if (key->source_type == cur->key.source_type &&
@@ -271,6 +289,9 @@ void avtab_destroy(struct avtab *h)
 		while (cur) {
 			temp = cur;
 			cur = cur->next;
+			if (temp->key.specified & AVTAB_XPERMS)
+				kmem_cache_free(avtab_xperms_cachep,
+						temp->datum.u.xperms);
 			kmem_cache_free(avtab_node_cachep, temp);
 		}
 	}
@@ -359,7 +380,10 @@ static uint16_t spec_order[] = {
 	AVTAB_AUDITALLOW,
 	AVTAB_TRANSITION,
 	AVTAB_CHANGE,
-	AVTAB_MEMBER
+	AVTAB_MEMBER,
+	AVTAB_XPERMS_ALLOWED,
+	AVTAB_XPERMS_AUDITALLOW,
+	AVTAB_XPERMS_DONTAUDIT
 };
 
 int avtab_read_item(struct avtab *a, void *fp, struct policydb *pol,
@@ -369,10 +393,11 @@ int avtab_read_item(struct avtab *a, void *fp, struct policydb *pol,
 {
 	__le16 buf16[4];
 	u16 enabled;
-	__le32 buf32[7];
 	u32 items, items2, val, vers = pol->policyvers;
 	struct avtab_key key;
 	struct avtab_datum datum;
+	struct avtab_extended_perms xperms;
+	__le32 buf32[ARRAY_SIZE(xperms.perms.p)];
 	int i, rc;
 	unsigned set;
 
@@ -429,11 +454,15 @@ int avtab_read_item(struct avtab *a, void *fp, struct policydb *pol,
 			printk(KERN_ERR "SELinux: avtab: entry has both access vectors and types\n");
 			return -EINVAL;
 		}
+		if (val & AVTAB_XPERMS) {
+			printk(KERN_ERR "SELinux: avtab: entry has extended permissions\n");
+			return -EINVAL;
+		}
 
 		for (i = 0; i < ARRAY_SIZE(spec_order); i++) {
 			if (val & spec_order[i]) {
 				key.specified = spec_order[i] | enabled;
-				datum.data = le32_to_cpu(buf32[items++]);
+				datum.u.data = le32_to_cpu(buf32[items++]);
 				rc = insertf(a, &key, &datum, p);
 				if (rc)
 					return rc;
@@ -476,14 +505,42 @@ int avtab_read_item(struct avtab *a, void *fp, struct policydb *pol,
 		return -EINVAL;
 	}
 
+	if ((vers < POLICYDB_VERSION_XPERMS_IOCTL) &&
+			(key.specified & AVTAB_XPERMS)) {
+		printk(KERN_ERR "SELinux:  avtab:  policy version %u does not "
+				"support extended permissions rules and one "
+				"was specified\n", vers);
+		return -EINVAL;
+	} else if (key.specified & AVTAB_XPERMS) {
+		memset(&xperms, 0, sizeof(struct avtab_extended_perms));
+		rc = next_entry(&xperms.specified, fp, sizeof(u8));
+		if (rc) {
+			printk(KERN_ERR "SELinux: avtab: truncated entry\n");
+			return rc;
+		}
+		rc = next_entry(&xperms.driver, fp, sizeof(u8));
+		if (rc) {
+			printk(KERN_ERR "SELinux: avtab: truncated entry\n");
+			return rc;
+		}
+		rc = next_entry(buf32, fp, sizeof(u32)*ARRAY_SIZE(xperms.perms.p));
+		if (rc) {
+			printk(KERN_ERR "SELinux: avtab: truncated entry\n");
+			return rc;
+		}
+		for (i = 0; i < ARRAY_SIZE(xperms.perms.p); i++)
+			xperms.perms.p[i] = le32_to_cpu(buf32[i]);
+		datum.u.xperms = &xperms;
+	} else {
 		rc = next_entry(buf32, fp, sizeof(u32));
 		if (rc) {
 			printk(KERN_ERR "SELinux: avtab: truncated entry\n");
 			return rc;
 		}
-	datum.data = le32_to_cpu(*buf32);
+		datum.u.data = le32_to_cpu(*buf32);
+	}
 	if ((key.specified & AVTAB_TYPE) &&
-	    !policydb_type_isvalid(pol, datum.data)) {
+	    !policydb_type_isvalid(pol, datum.u.data)) {
 		printk(KERN_ERR "SELinux: avtab: invalid type\n");
 		return -EINVAL;
 	}
@@ -543,8 +600,9 @@ int avtab_read(struct avtab *a, void *fp, struct policydb *pol)
 int avtab_write_item(struct policydb *p, struct avtab_node *cur, void *fp)
 {
 	__le16 buf16[4];
-	__le32 buf32[1];
+	__le32 buf32[ARRAY_SIZE(cur->datum.u.xperms->perms.p)];
 	int rc;
+	unsigned int i;
 
 	buf16[0] = cpu_to_le16(cur->key.source_type);
 	buf16[1] = cpu_to_le16(cur->key.target_type);
@@ -553,8 +611,22 @@ int avtab_write_item(struct policydb *p, struct avtab_node *cur, void *fp)
 	rc = put_entry(buf16, sizeof(u16), 4, fp);
 	if (rc)
 		return rc;
-	buf32[0] = cpu_to_le32(cur->datum.data);
+
+	if (cur->key.specified & AVTAB_XPERMS) {
+		rc = put_entry(&cur->datum.u.xperms->specified, sizeof(u8), 1, fp);
+		if (rc)
+			return rc;
+		rc = put_entry(&cur->datum.u.xperms->driver, sizeof(u8), 1, fp);
+		if (rc)
+			return rc;
+		for (i = 0; i < ARRAY_SIZE(cur->datum.u.xperms->perms.p); i++)
+			buf32[i] = cpu_to_le32(cur->datum.u.xperms->perms.p[i]);
+		rc = put_entry(buf32, sizeof(u32),
+				ARRAY_SIZE(cur->datum.u.xperms->perms.p), fp);
+	} else {
+		buf32[0] = cpu_to_le32(cur->datum.u.data);
 		rc = put_entry(buf32, sizeof(u32), 1, fp);
+	}
 	if (rc)
 		return rc;
 	return 0;
@@ -588,9 +660,13 @@ void avtab_cache_init(void)
 	avtab_node_cachep = kmem_cache_create("avtab_node",
 					      sizeof(struct avtab_node),
 					      0, SLAB_PANIC, NULL);
+	avtab_xperms_cachep = kmem_cache_create("avtab_extended_perms",
+						sizeof(struct avtab_extended_perms),
+						0, SLAB_PANIC, NULL);
 }
 
 void avtab_cache_destroy(void)
 {
 	kmem_cache_destroy(avtab_node_cachep);
+	kmem_cache_destroy(avtab_xperms_cachep);
 }

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 {
+	union {
 		u32 data; /* access vector or type value */
+		struct avtab_extended_perms *xperms;
+	} u;
 };
 
 struct avtab_node {

security/selinux/ss/conditional.c

@@ -15,6 +15,7 @@
 
 #include "security.h"
 #include "conditional.h"
+#include "services.h"
 
 /*
  * cond_evaluate_expr evaluates a conditional expr
@@ -612,21 +613,39 @@ int cond_write_list(struct policydb *p, struct cond_node *list, void *fp)
 
 	return 0;
 }
+
+void cond_compute_xperms(struct avtab *ctab, struct avtab_key *key,
+		struct extended_perms_decision *xpermd)
+{
+	struct avtab_node *node;
+
+	if (!ctab || !key || !xpermd)
+		return;
+
+	for (node = avtab_search_node(ctab, key); node;
+			node = avtab_search_node_next(node, key->specified)) {
+		if (node->key.specified & AVTAB_ENABLED)
+			services_compute_xperms_decision(xpermd, node);
+	}
+	return;
+
+}
 /* Determine whether additional permissions are granted by the conditional
  * av table, and if so, add them to the result
  */
-void cond_compute_av(struct avtab *ctab, struct avtab_key *key, struct av_decision *avd)
+void cond_compute_av(struct avtab *ctab, struct avtab_key *key,
+		struct av_decision *avd, struct extended_perms *xperms)
 {
 	struct avtab_node *node;
 
-	if (!ctab || !key || !avd)
+	if (!ctab || !key || !avd || !xperms)
 		return;
 
 	for (node = avtab_search_node(ctab, key); node;
 				node = avtab_search_node_next(node, key->specified)) {
 		if ((u16)(AVTAB_ALLOWED|AVTAB_ENABLED) ==
 		    (node->key.specified & (AVTAB_ALLOWED|AVTAB_ENABLED)))
-			avd->allowed |= node->datum.data;
+			avd->allowed |= node->datum.u.data;
 		if ((u16)(AVTAB_AUDITDENY|AVTAB_ENABLED) ==
 		    (node->key.specified & (AVTAB_AUDITDENY|AVTAB_ENABLED)))
 			/* Since a '0' in an auditdeny mask represents a
@@ -634,10 +653,13 @@ void cond_compute_av(struct avtab *ctab, struct avtab_key *key, struct av_decisi
 			 * the '&' operand to ensure that all '0's in the mask
 			 * are retained (much unlike the allow and auditallow cases).
 			 */
-			avd->auditdeny &= node->datum.data;
+			avd->auditdeny &= node->datum.u.data;
 		if ((u16)(AVTAB_AUDITALLOW|AVTAB_ENABLED) ==
 		    (node->key.specified & (AVTAB_AUDITALLOW|AVTAB_ENABLED)))
-			avd->auditallow |= node->datum.data;
+			avd->auditallow |= node->datum.u.data;
+		if ((node->key.specified & AVTAB_ENABLED) &&
+				(node->key.specified & AVTAB_XPERMS))
+			services_compute_xperms_drivers(xperms, node);
 	}
 	return;
 }

security/selinux/ss/conditional.h

@@ -73,8 +73,10 @@ int cond_read_list(struct policydb *p, void *fp);
 int cond_write_bool(void *key, void *datum, void *ptr);
 int cond_write_list(struct policydb *p, struct cond_node *list, void *fp);
 
-void cond_compute_av(struct avtab *ctab, struct avtab_key *key, struct av_decision *avd);
-
+void cond_compute_av(struct avtab *ctab, struct avtab_key *key,
+		struct av_decision *avd, struct extended_perms *xperms);
+void cond_compute_xperms(struct avtab *ctab, struct avtab_key *key,
+		struct extended_perms_decision *xpermd);
 int evaluate_cond_node(struct policydb *p, struct cond_node *node);
 
 #endif /* _CONDITIONAL_H_ */

security/selinux/ss/policydb.c

@@ -148,6 +148,11 @@ static struct policydb_compat_info policydb_compat[] = {
 		.sym_num	= SYM_NUM,
 		.ocon_num	= OCON_NUM,
 	},
+	{
+		.version	= POLICYDB_VERSION_XPERMS_IOCTL,
+		.sym_num	= SYM_NUM,
+		.ocon_num	= OCON_NUM,
+	},
 };
 
 static struct policydb_compat_info *policydb_lookup_compat(int version)

security/selinux/ss/services.h

@@ -11,5 +11,11 @@
 
 extern struct policydb policydb;
 
+void services_compute_xperms_drivers(struct extended_perms *xperms,
+				struct avtab_node *node);
+
+void services_compute_xperms_decision(struct extended_perms_decision *xpermd,
+					struct avtab_node *node);
+
 #endif	/* _SS_SERVICES_H_ */