[PATCH 67/90] Smack: Detect if secmarks can be safely used

[Casey Schaufler]

Utilize the security_secmark_refcount_in() hooks to determine
if Smack can safely assume that IP secmarks are not being used
by another LSM. Only use secmarks if they can be determined to
belong to Smack.

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
---
 security/smack/smack.h           | 15 +++++++++++++++
 security/smack/smack_lsm.c       | 16 +++++-----------
 security/smack/smack_netfilter.c | 25 +++++++++++++++++++++++--
 3 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/security/smack/smack.h b/security/smack/smack.h
index 7cc3a3382fee..66ad1c175002 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -544,4 +544,19 @@ static inline void smk_ad_setfield_u_net_sk(struct smk_audit_info *a,
 }
 #endif
 
+#ifdef CONFIG_SECURITY_SMACK_NETFILTER
+extern bool smack_use_secmark;
+void smack_secmark_refcount_inc(void);
+
+static inline bool smk_use_secmark(void)
+{
+	return smack_use_secmark;
+}
+#else
+static inline bool smk_use_secmark(void)
+{
+	return false;
+}
+#endif
+
 #endif  /* _SECURITY_SMACK_H */
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index aaca4ba53032..d76aa0fc37a4 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3828,7 +3828,7 @@ static int smk_skb_to_addr_ipv6(struct sk_buff *skb, struct sockaddr_in6 *sip)
  */
 static struct smack_known *smack_from_skb(struct sk_buff *skb)
 {
-	if (skb == NULL || skb->secmark == 0)
+	if (skb == NULL || skb->secmark == 0 || !smk_use_secmark())
 		return NULL;
 
 	return smack_from_secid(skb->secmark);
@@ -3862,7 +3862,6 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
 	switch (family) {
 	case PF_INET:
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
 		/*
 		 * If there is a secmark use it rather than the CIPSO label.
 		 * If there is no secmark fall back to CIPSO.
@@ -3871,7 +3870,6 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		skp = smack_from_skb(skb);
 		if (skp)
 			goto access_check;
-#endif /* CONFIG_SECURITY_SMACK_NETFILTER */
 		/*
 		 * Translate what netlabel gave us.
 		 */
@@ -3885,9 +3883,8 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 
 		netlbl_secattr_destroy(&secattr);
 
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
 access_check:
-#endif
+
 #ifdef CONFIG_AUDIT
 		smk_ad_init_net(&ad, __func__, LSM_AUDIT_DATA_NET, &net);
 		ad.a.u.net->family = family;
@@ -4014,13 +4011,11 @@ static int smack_socket_getpeersec_dgram(struct socket *sock,
 		s = ssp->smk_out->smk_secid;
 		break;
 	case PF_INET:
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
 		skp = smack_from_skb(skb);
 		if (skp) {
 			s = skp->smk_secid;
 			break;
 		}
-#endif
 		/*
 		 * Translate what netlabel gave us.
 		 */
@@ -4110,7 +4105,6 @@ static int smack_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 	}
 #endif /* CONFIG_IPV6 */
 
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
 	/*
 	 * If there is a secmark use it rather than the CIPSO label.
 	 * If there is no secmark fall back to CIPSO.
@@ -4119,7 +4113,6 @@ static int smack_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 	skp = smack_from_skb(skb);
 	if (skp)
 		goto access_check;
-#endif /* CONFIG_SECURITY_SMACK_NETFILTER */
 
 	netlbl_secattr_init(&secattr);
 	rc = netlbl_skbuff_getattr(skb, family, &secattr);
@@ -4129,9 +4122,7 @@ static int smack_inet_conn_request(struct sock *sk, struct sk_buff *skb,
 		skp = &smack_known_huh;
 	netlbl_secattr_destroy(&secattr);
 
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
 access_check:
-#endif
 
 #ifdef CONFIG_AUDIT
 	smk_ad_init_net(&ad, __func__, LSM_AUDIT_DATA_NET, &net);
@@ -4708,6 +4699,9 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(sk_alloc_security, smack_sk_alloc_security),
 #ifdef SMACK_IPV6_PORT_LABELING
 	LSM_HOOK_INIT(sk_free_security, smack_sk_free_security),
+#endif
+#ifdef CONFIG_SECURITY_SMACK_NETFILTER
+	LSM_HOOK_INIT(secmark_refcount_inc, smack_secmark_refcount_inc),
 #endif
 	LSM_HOOK_INIT(sock_graft, smack_sock_graft),
 	LSM_HOOK_INIT(inet_conn_request, smack_inet_conn_request),
diff --git a/security/smack/smack_netfilter.c b/security/smack/smack_netfilter.c
index 701a1cc1bdcc..ea45b173f8ca 100644
--- a/security/smack/smack_netfilter.c
+++ b/security/smack/smack_netfilter.c
@@ -21,6 +21,15 @@
 #include <net/net_namespace.h>
 #include "smack.h"
 
+bool smack_use_secmark;
+static bool smack_checked_secmark;
+
+void smack_secmark_refcount_inc(void)
+{
+        smack_use_secmark = true;
+	pr_info("Smack: Using network secmarks.\n");
+}
+
 #if IS_ENABLED(CONFIG_IPV6)
 
 static unsigned int smack_ipv6_output(void *priv,
@@ -31,7 +40,13 @@ static unsigned int smack_ipv6_output(void *priv,
 	struct socket_smack *ssp;
 	struct smack_known *skp;
 
-	if (sk && smack_sock(sk)) {
+	if (!smack_checked_secmark) {
+		security_secmark_refcount_inc();
+		security_secmark_refcount_dec();
+		smack_checked_secmark = true;
+	}
+
+	if (smack_use_secmark && sk && smack_sock(sk)) {
 		ssp = smack_sock(sk);
 		skp = ssp->smk_out;
 		skb->secmark = skp->smk_secid;
@@ -49,7 +64,13 @@ static unsigned int smack_ipv4_output(void *priv,
 	struct socket_smack *ssp;
 	struct smack_known *skp;
 
-	if (sk && smack_sock(sk)) {
+	if (!smack_checked_secmark) {
+		security_secmark_refcount_inc();
+		security_secmark_refcount_dec();
+		smack_checked_secmark = true;
+	}
+
+	if (smack_use_secmark && sk && smack_sock(sk)) {
 		ssp = smack_sock(sk);
 		skp = ssp->smk_out;
 		skb->secmark = skp->smk_secid;
-- 
2.19.1