[PATCH 1/2] LSM: Exclusive secmark usage

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

The network secmark can only be used by one security module
at a time. Establish mechanism to identify to security modules
whether they have access to the secmark. SELinux already
incorparates mechanism, but it has to be added to Smack and
AppArmor.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 include/linux/lsm_hooks.h        |  1 +
 security/apparmor/include/net.h  |  5 +++++
 security/apparmor/lsm.c          |  7 ++++---
 security/security.c              |  6 ++++++
 security/selinux/hooks.c         |  4 +++-
 security/smack/smack.h           |  5 +++++
 security/smack/smack_lsm.c       |  3 ++-
 security/smack/smack_netfilter.c | 10 ++++++++--
 8 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 090d1d3e19fe..69c1b509577a 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -116,6 +116,7 @@ struct lsm_blob_sizes {
 	int lbs_xattr_count; /* number of xattr slots in new_xattrs array */
 	int lbs_tun_dev;
 	int lbs_bdev;
+	bool lbs_secmark; /* expressed desire for secmark use */
 };
 
 /*
diff --git a/security/apparmor/include/net.h b/security/apparmor/include/net.h
index 0d0b0ce42723..1199918448a9 100644
--- a/security/apparmor/include/net.h
+++ b/security/apparmor/include/net.h
@@ -52,6 +52,11 @@ struct aa_sk_ctx {
 	struct aa_label __rcu *peer_lastupdate;	/* ptr cmp only, no deref */
 };
 
+static inline bool aa_secmark(void)
+{
+	return apparmor_blob_sizes.lbs_secmark;
+}
+
 static inline struct aa_sk_ctx *aa_sock(const struct sock *sk)
 {
 	return sk->sk_security + apparmor_blob_sizes.lbs_sock;
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 8e1cc229b41b..34eac7da80e6 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1512,7 +1512,7 @@ static int apparmor_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	struct aa_sk_ctx *ctx = aa_sock(sk);
 	int error;
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return 0;
 
 	/*
@@ -1641,7 +1641,7 @@ static int apparmor_inet_conn_request(const struct sock *sk, struct sk_buff *skb
 	struct aa_sk_ctx *ctx = aa_sock(sk);
 	int error;
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return 0;
 
 	rcu_read_lock();
@@ -1661,6 +1661,7 @@ struct lsm_blob_sizes apparmor_blob_sizes __ro_after_init = {
 	.lbs_file = sizeof(struct aa_file_ctx),
 	.lbs_task = sizeof(struct aa_task_ctx),
 	.lbs_sock = sizeof(struct aa_sk_ctx),
+	.lbs_secmark = true,
 };
 
 static const struct lsm_id apparmor_lsmid = {
@@ -2360,7 +2361,7 @@ static unsigned int apparmor_ip_postroute(void *priv,
 	struct sock *sk;
 	int error;
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return NF_ACCEPT;
 
 	sk = skb_to_full_sk(skb);
diff --git a/security/security.c b/security/security.c
index ad163f06bf7a..e59e3d403de6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -283,6 +283,12 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
 	lsm_set_blob_size(&needed->lbs_xattr_count,
 			  &blob_sizes.lbs_xattr_count);
 	lsm_set_blob_size(&needed->lbs_bdev, &blob_sizes.lbs_bdev);
+	if (needed->lbs_secmark) {
+		if (blob_sizes.lbs_secmark)
+			needed->lbs_secmark = false;
+		else
+			blob_sizes.lbs_secmark = true;
+	}
 }
 
 /* Prepare LSM for initialization. */
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c95a5874bf7d..5b6db7d8effb 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -164,7 +164,8 @@ __setup("checkreqprot=", checkreqprot_setup);
  */
 static int selinux_secmark_enabled(void)
 {
-	return (selinux_policycap_alwaysnetwork() ||
+	return selinux_blob_sizes.lbs_secmark &&
+	       (selinux_policycap_alwaysnetwork() ||
 		atomic_read(&selinux_secmark_refcount));
 }
 
@@ -7183,6 +7184,7 @@ struct lsm_blob_sizes selinux_blob_sizes __ro_after_init = {
 	.lbs_xattr_count = SELINUX_INODE_INIT_XATTRS,
 	.lbs_tun_dev = sizeof(struct tun_security_struct),
 	.lbs_ib = sizeof(struct ib_security_struct),
+	.lbs_secmark = true,
 };
 
 #ifdef CONFIG_PERF_EVENTS
diff --git a/security/smack/smack.h b/security/smack/smack.h
index bf6a6ed3946c..89bf62ad60f1 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -383,6 +383,11 @@ static inline int smk_inode_transmutable(const struct inode *isp)
 	return (sip->smk_flags & SMK_INODE_TRANSMUTE) != 0;
 }
 
+static inline bool smack_secmark(void)
+{
+	return smack_blob_sizes.lbs_secmark;
+}
+
 /*
  * Present a pointer to the smack label entry in an inode blob.
  */
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index fc340a6f0dde..ee86818633c1 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4102,7 +4102,7 @@ static int smk_skb_to_addr_ipv6(struct sk_buff *skb, struct sockaddr_in6 *sip)
 #ifdef CONFIG_NETWORK_SECMARK
 static struct smack_known *smack_from_skb(struct sk_buff *skb)
 {
-	if (skb == NULL || skb->secmark == 0)
+	if (!smack_secmark() || skb == NULL || skb->secmark == 0)
 		return NULL;
 
 	return smack_from_secid(skb->secmark);
@@ -5030,6 +5030,7 @@ struct lsm_blob_sizes smack_blob_sizes __ro_after_init = {
 	.lbs_sock = sizeof(struct socket_smack),
 	.lbs_superblock = sizeof(struct superblock_smack),
 	.lbs_xattr_count = SMACK_INODE_INIT_XATTRS,
+	.lbs_secmark = true,
 };
 
 static const struct lsm_id smack_lsmid = {
diff --git a/security/smack/smack_netfilter.c b/security/smack/smack_netfilter.c
index 8fd747b3653a..2e82051b3998 100644
--- a/security/smack/smack_netfilter.c
+++ b/security/smack/smack_netfilter.c
@@ -26,7 +26,7 @@ static unsigned int smack_ip_output(void *priv,
 	struct socket_smack *ssp;
 	struct smack_known *skp;
 
-	if (sk) {
+	if (smack_secmark() && sk) {
 		ssp = smack_sock(sk);
 		skp = ssp->smk_out;
 		skb->secmark = skp->smk_secid;
@@ -54,12 +54,18 @@ static const struct nf_hook_ops smack_nf_ops[] = {
 
 static int __net_init smack_nf_register(struct net *net)
 {
+	if (!smack_secmark())
+		return 0;
+
 	return nf_register_net_hooks(net, smack_nf_ops,
 				     ARRAY_SIZE(smack_nf_ops));
 }
 
 static void __net_exit smack_nf_unregister(struct net *net)
 {
+	if (!smack_secmark())
+		return;
+
 	nf_unregister_net_hooks(net, smack_nf_ops, ARRAY_SIZE(smack_nf_ops));
 }
 
@@ -70,7 +76,7 @@ static struct pernet_operations smack_net_ops = {
 
 static int __init smack_nf_ip_init(void)
 {
-	if (smack_enabled == 0)
+	if (smack_enabled == 0 || !smack_secmark())
 		return 0;
 
 	printk(KERN_DEBUG "Smack: Registering netfilter hooks\n");
-- 
2.51.0