[PATCH v38 28/39] LSM: security_secid_to_secctx module selection

[Casey Schaufler <casey@schaufler-ca.com>]

Add a parameter to security_secid_to_secctx() to identify
which of the security modules that may be active should
provide the security context. If the parameter is greater
than or equal to zero, the security module associated with
that LSM "slot" is used. If the value is LSMBLOB_DISPLAY
the "interface lsm" is used. If the value is LSMBLOB_FIRST
the first security module providing a hook is used.

The integrity IMA subsystem has chosen to always use the
LSMBLOB_FIRST behavior, regardless of the lsm_display values.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 drivers/android/binder.c                |  2 +-
 include/linux/security.h                |  7 +++++--
 include/net/scm.h                       |  2 +-
 kernel/audit.c                          |  4 ++--
 kernel/auditsc.c                        |  7 ++++---
 net/ipv4/ip_sockglue.c                  |  2 +-
 net/netfilter/nf_conntrack_netlink.c    |  4 ++--
 net/netfilter/nf_conntrack_standalone.c |  2 +-
 net/netfilter/nfnetlink_queue.c         |  2 +-
 net/netlabel/netlabel_unlabeled.c       | 11 +++++++----
 net/netlabel/netlabel_user.c            |  2 +-
 security/security.c                     | 20 ++++++++++++++++++--
 12 files changed, 44 insertions(+), 21 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index ff8f35b9bd1b..2206f7275349 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3172,7 +3172,7 @@ static void binder_transaction(struct binder_proc *proc,
 		size_t added_size;
 
 		security_cred_getsecid(proc->cred, &blob);
-		ret = security_secid_to_secctx(&blob, &lsmctx);
+		ret = security_secid_to_secctx(&blob, &lsmctx, LSMBLOB_DISPLAY);
 		if (ret) {
 			binder_txn_error("%d:%d failed to get security context\n",
 				thread->pid, proc->pid);
diff --git a/include/linux/security.h b/include/linux/security.h
index 4f2c1bb857be..170b303e9122 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -203,6 +203,8 @@ struct lsmblob {
 #define LSMBLOB_INVALID		-1	/* Not a valid LSM slot number */
 #define LSMBLOB_NEEDED		-2	/* Slot requested on initialization */
 #define LSMBLOB_NOT_NEEDED	-3	/* Slot not requested */
+#define LSMBLOB_DISPLAY		-4	/* Use the "interface_lsm" slot */
+#define LSMBLOB_FIRST		-5	/* Use the first slot */
 
 /**
  * lsmblob_init - initialize a lsmblob structure
@@ -646,7 +648,8 @@ int security_getprocattr(struct task_struct *p, int lsmid, char *name,
 int security_setprocattr(int lsmid, const char *name, void *value, size_t size);
 int security_netlink_send(struct sock *sk, struct sk_buff *skb);
 int security_ismaclabel(const char *name);
-int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp);
+int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp,
+			     int ilsm);
 int security_secctx_to_secid(const char *secdata, u32 seclen,
 			     struct lsmblob *blob);
 void security_release_secctx(struct lsmcontext *cp);
@@ -1507,7 +1510,7 @@ static inline int security_ismaclabel(const char *name)
 }
 
 static inline int security_secid_to_secctx(struct lsmblob *blob,
-					   struct lsmcontext *cp)
+					   struct lsmcontext *cp, int ilsm)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/include/net/scm.h b/include/net/scm.h
index b77a52f93389..f4d567d4885e 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -101,7 +101,7 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
 		 * and the infrastructure will know which it is.
 		 */
 		lsmblob_init(&lb, scm->secid);
-		err = security_secid_to_secctx(&lb, &context);
+		err = security_secid_to_secctx(&lb, &context, LSMBLOB_DISPLAY);
 
 		if (!err) {
 			put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, context.len,
diff --git a/kernel/audit.c b/kernel/audit.c
index 154fe4c40bb8..98c5ace6f453 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1464,7 +1464,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 		if (lsmblob_is_set(&audit_sig_lsm)) {
 			err = security_secid_to_secctx(&audit_sig_lsm,
-						       &context);
+						       &context, LSMBLOB_FIRST);
 			if (err)
 				return err;
 		}
@@ -2176,7 +2176,7 @@ int audit_log_task_context(struct audit_buffer *ab)
 	if (!lsmblob_is_set(&blob))
 		return 0;
 
-	error = security_secid_to_secctx(&blob, &context);
+	error = security_secid_to_secctx(&blob, &context, LSMBLOB_FIRST);
 
 	if (error) {
 		if (error != -EINVAL)
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index c3d4617d31c7..ca00187b4864 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1107,7 +1107,7 @@ static int audit_log_pid_context(struct audit_context *context, pid_t pid,
 			 from_kuid(&init_user_ns, auid),
 			 from_kuid(&init_user_ns, uid), sessionid);
 	if (lsmblob_is_set(blob)) {
-		if (security_secid_to_secctx(blob, &lsmctx)) {
+		if (security_secid_to_secctx(blob, &lsmctx, LSMBLOB_FIRST)) {
 			audit_log_format(ab, " obj=(none)");
 			rc = 1;
 		} else {
@@ -1400,7 +1400,8 @@ static void show_special(struct audit_context *context, int *call_panic)
 			struct lsmblob blob;
 
 			lsmblob_init(&blob, osid);
-			if (security_secid_to_secctx(&blob, &lsmcxt)) {
+			if (security_secid_to_secctx(&blob, &lsmcxt,
+						     LSMBLOB_FIRST)) {
 				audit_log_format(ab, " osid=%u", osid);
 				*call_panic = 1;
 			} else {
@@ -1568,7 +1569,7 @@ static void audit_log_name(struct audit_context *context, struct audit_names *n,
 		struct lsmcontext lsmctx;
 
 		lsmblob_init(&blob, n->osid);
-		if (security_secid_to_secctx(&blob, &lsmctx)) {
+		if (security_secid_to_secctx(&blob, &lsmctx, LSMBLOB_FIRST)) {
 			audit_log_format(ab, " osid=%u", n->osid);
 			if (call_panic)
 				*call_panic = 2;
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index ec3ef548264d..4aaac7b9b452 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -140,7 +140,7 @@ static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
 		return;
 
 	lsmblob_init(&lb, secid);
-	err = security_secid_to_secctx(&lb, &context);
+	err = security_secid_to_secctx(&lb, &context, LSMBLOB_DISPLAY);
 	if (err)
 		return;
 
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 93855cd7ce4b..dce0994272ed 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -353,7 +353,7 @@ static int ctnetlink_dump_secctx(struct sk_buff *skb, const struct nf_conn *ct)
 	 * security_secid_to_secctx() will know which security module
 	 * to use to create the secctx.  */
 	lsmblob_init(&blob, ct->secmark);
-	ret = security_secid_to_secctx(&blob, &context);
+	ret = security_secid_to_secctx(&blob, &context, LSMBLOB_DISPLAY);
 	if (ret)
 		return 0;
 
@@ -663,7 +663,7 @@ static inline int ctnetlink_secctx_size(const struct nf_conn *ct)
 	int len;
 	struct lsmblob blob;
 
-	len = security_secid_to_secctx(&blob, NULL);
+	len = security_secid_to_secctx(&blob, NULL, LSMBLOB_DISPLAY);
 	if (len <= 0)
 		return 0;
 
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index b5b301f5b3f7..fbeeeb7080bf 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -180,7 +180,7 @@ static void ct_show_secctx(struct seq_file *s, const struct nf_conn *ct)
 	struct lsmcontext context;
 
 	lsmblob_init(&blob, ct->secmark);
-	ret = security_secid_to_secctx(&blob, &context);
+	ret = security_secid_to_secctx(&blob, &context, LSMBLOB_DISPLAY);
 	if (ret)
 		return;
 
diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 3a7d1a693c5e..bef123b1250c 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -316,7 +316,7 @@ static void nfqnl_get_sk_secctx(struct sk_buff *skb, struct lsmcontext *context)
 		 * blob. security_secid_to_secctx() will know which security
 		 * module to use to create the secctx.  */
 		lsmblob_init(&blob, skb->secmark);
-		security_secid_to_secctx(&blob, context);
+		security_secid_to_secctx(&blob, context, LSMBLOB_DISPLAY);
 	}
 
 	read_unlock_bh(&skb->sk->sk_callback_lock);
diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
index ae2f49f3398d..050753d2f2bb 100644
--- a/net/netlabel/netlabel_unlabeled.c
+++ b/net/netlabel/netlabel_unlabeled.c
@@ -437,7 +437,8 @@ int netlbl_unlhsh_add(struct net *net,
 unlhsh_add_return:
 	rcu_read_unlock();
 	if (audit_buf != NULL) {
-		if (security_secid_to_secctx(lsmblob, &context) == 0) {
+		if (security_secid_to_secctx(lsmblob, &context,
+					     LSMBLOB_FIRST) == 0) {
 			audit_log_format(audit_buf, " sec_obj=%s",
 					 context.context);
 			security_release_secctx(&context);
@@ -491,7 +492,8 @@ static int netlbl_unlhsh_remove_addr4(struct net *net,
 					  addr->s_addr, mask->s_addr);
 		dev_put(dev);
 		if (entry != NULL &&
-		    security_secid_to_secctx(&entry->lsmblob, &context) == 0) {
+		    security_secid_to_secctx(&entry->lsmblob, &context,
+					     LSMBLOB_FIRST) == 0) {
 			audit_log_format(audit_buf, " sec_obj=%s",
 					 context.context);
 			security_release_secctx(&context);
@@ -550,7 +552,8 @@ static int netlbl_unlhsh_remove_addr6(struct net *net,
 					  addr, mask);
 		dev_put(dev);
 		if (entry != NULL &&
-		    security_secid_to_secctx(&entry->lsmblob, &context) == 0) {
+		    security_secid_to_secctx(&entry->lsmblob, &context,
+					     LSMBLOB_FIRST) == 0) {
 			audit_log_format(audit_buf, " sec_obj=%s",
 					 context.context);
 			security_release_secctx(&context);
@@ -1120,7 +1123,7 @@ static int netlbl_unlabel_staticlist_gen(u32 cmd,
 		lsmb = (struct lsmblob *)&addr6->lsmblob;
 	}
 
-	ret_val = security_secid_to_secctx(lsmb, &context);
+	ret_val = security_secid_to_secctx(lsmb, &context, LSMBLOB_FIRST);
 	if (ret_val != 0)
 		goto list_cb_failure;
 	ret_val = nla_put(cb_arg->skb,
diff --git a/net/netlabel/netlabel_user.c b/net/netlabel/netlabel_user.c
index 951ba0639d20..1941877fd16f 100644
--- a/net/netlabel/netlabel_user.c
+++ b/net/netlabel/netlabel_user.c
@@ -100,7 +100,7 @@ struct audit_buffer *netlbl_audit_start_common(int type,
 
 	lsmblob_init(&blob, audit_info->secid);
 	if (audit_info->secid != 0 &&
-	    security_secid_to_secctx(&blob, &context) == 0) {
+	    security_secid_to_secctx(&blob, &context, LSMBLOB_FIRST) == 0) {
 		audit_log_format(audit_buf, " subj=%s", context.context);
 		security_release_secctx(&context);
 	}
diff --git a/security/security.c b/security/security.c
index d31989e4bc25..0456bb6503d5 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2334,20 +2334,36 @@ EXPORT_SYMBOL(security_ismaclabel);
  * security_secid_to_secctx - convert secid to secctx
  * @blob: set of secids
  * @cp: lsm context into which result is put
+ * @ilsm: which security module to report
  *
  * Translate secid information into a secctx string.
  * Return a negative value on error.
  * If cp is NULL return the length of the string.
  * Otherwise, return 0.
  */
-int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp)
+int security_secid_to_secctx(struct lsmblob *blob, struct lsmcontext *cp,
+			     int ilsm)
 {
 	struct security_hook_list *hp;
-	int ilsm = lsm_task_ilsm(current);
 
 	if (cp)
 		memset(cp, 0, sizeof(*cp));
 
+	/*
+	 * ilsm either is the slot number use for formatting
+	 * or an instruction on which relative slot to use.
+	 */
+	if (ilsm == LSMBLOB_DISPLAY)
+		ilsm = lsm_task_ilsm(current);
+	else if (ilsm == LSMBLOB_FIRST)
+		ilsm = LSMBLOB_INVALID;
+	else if (ilsm < 0) {
+		WARN_ONCE(true, "LSM: %s unknown interface LSM\n", __func__);
+		ilsm = LSMBLOB_INVALID;
+	} else if (ilsm >= lsm_slot) {
+		WARN_ONCE(true, "LSM: %s invalid interface LSM\n", __func__);
+		ilsm = LSMBLOB_INVALID;
+	}
 	hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) {
 		if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
 			continue;
-- 
2.37.3

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