[v7,02/16] Smack: Detect if secmarks can be safely used
diff mbox series

Message ID 20190807224245.10798-4-casey@schaufler-ca.com
State New
Headers show
Series
  • LSM: Full module stacking
Related show

Commit Message

Casey Schaufler Aug. 7, 2019, 10:42 p.m. UTC
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@schaufler-ca.com>
---
 security/smack/smack.h           | 16 ++++++++++
 security/smack/smack_lsm.c       | 54 +++++++++++++++++++-------------
 security/smack/smack_netfilter.c | 39 +++++++++++++++++++++--
 3 files changed, 85 insertions(+), 24 deletions(-)

Patch
diff mbox series

diff --git a/security/smack/smack.h b/security/smack/smack.h
index 039bf5de56b4..f28db5a42b7b 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -545,4 +545,20 @@  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);
+void smack_secmark_refcount_dec(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 40c75205a914..341a9927ed5c 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3801,6 +3801,20 @@  static int smk_skb_to_addr_ipv6(struct sk_buff *skb, struct sockaddr_in6 *sip)
 }
 #endif /* CONFIG_IPV6 */
 
+/**
+ * smack_from_skb - Smack data from the secmark in an skb
+ * @skb: packet
+ *
+ * Returns smack_known of the secmark or NULL if that won't work.
+ */
+static struct smack_known *smack_from_skb(struct sk_buff *skb)
+{
+	if (skb == NULL || skb->secmark == 0 || !smk_use_secmark())
+		return NULL;
+
+	return smack_from_secid(skb->secmark);
+}
+
 /**
  * smack_socket_sock_rcv_skb - Smack packet delivery access check
  * @sk: socket
@@ -3829,17 +3843,14 @@  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.
 		 * The secmark is assumed to reflect policy better.
 		 */
-		if (skb && skb->secmark != 0) {
-			skp = smack_from_secid(skb->secmark);
+		skp = smack_from_skb(skb);
+		if (skp)
 			goto access_check;
-		}
-#endif /* CONFIG_SECURITY_SMACK_NETFILTER */
 		/*
 		 * Translate what netlabel gave us.
 		 */
@@ -3853,9 +3864,8 @@  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;
@@ -3881,9 +3891,8 @@  static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		    proto != IPPROTO_TCP && proto != IPPROTO_DCCP)
 			break;
 #ifdef SMACK_IPV6_SECMARK_LABELING
-		if (skb && skb->secmark != 0)
-			skp = smack_from_secid(skb->secmark);
-		else
+		skp = smack_from_skb(skb);
+		if (skp == NULL)
 			skp = smack_ipv6host_label(&sadd);
 		if (skp == NULL)
 			skp = smack_net_ambient;
@@ -3983,11 +3992,11 @@  static int smack_socket_getpeersec_dgram(struct socket *sock,
 		s = ssp->smk_out->smk_secid;
 		break;
 	case PF_INET:
-#ifdef CONFIG_SECURITY_SMACK_NETFILTER
-		s = skb->secmark;
-		if (s != 0)
+		skp = smack_from_skb(skb);
+		if (skp) {
+			s = skp->smk_secid;
 			break;
-#endif
+		}
 		/*
 		 * Translate what netlabel gave us.
 		 */
@@ -4003,7 +4012,9 @@  static int smack_socket_getpeersec_dgram(struct socket *sock,
 		break;
 	case PF_INET6:
 #ifdef SMACK_IPV6_SECMARK_LABELING
-		s = skb->secmark;
+		skp = smack_from_skb(skb);
+		if (skp)
+			s = skp->smk_secid;
 #endif
 		break;
 	}
@@ -4075,17 +4086,14 @@  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.
 	 * The secmark is assumed to reflect policy better.
 	 */
-	if (skb && skb->secmark != 0) {
-		skp = smack_from_secid(skb->secmark);
+	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);
@@ -4095,9 +4103,7 @@  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);
@@ -4673,6 +4679,10 @@  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),
+	LSM_HOOK_INIT(secmark_refcount_dec, smack_secmark_refcount_dec),
 #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..7b9c8d5d8408 100644
--- a/security/smack/smack_netfilter.c
+++ b/security/smack/smack_netfilter.c
@@ -21,6 +21,29 @@ 
 #include <net/net_namespace.h>
 #include "smack.h"
 
+bool smack_use_secmark;
+static bool smack_checked_secmark;
+
+/**
+ * smack_secmark_refcount_inc - Seize the secmark
+ *
+ * Note to the rest of the Smack code that secmarks may be used.
+ */
+void smack_secmark_refcount_inc(void)
+{
+	smack_use_secmark = true;
+	pr_info("Smack: Using network secmarks.\n");
+}
+
+/**
+ * smack_secmark_refcount_dec - Do nothing about the secmark
+ *
+ * Matches the incrementing function, but does nothing.
+ */
+void smack_secmark_refcount_dec(void)
+{
+}
+
 #if IS_ENABLED(CONFIG_IPV6)
 
 static unsigned int smack_ipv6_output(void *priv,
@@ -31,7 +54,13 @@  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 +78,13 @@  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;