[RFC PATCH 06/15] 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/lsm_init.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 5bc144c5f685..1ad9f8a86b10 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -122,6 +122,7 @@ struct lsm_blob_sizes {
 	unsigned int lbs_xattr_count; /* num xattr slots in new_xattrs array */
 	unsigned int lbs_tun_dev;
 	unsigned 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 c42ed8a73f1c..2e43e1e8303c 100644
--- a/security/apparmor/include/net.h
+++ b/security/apparmor/include/net.h
@@ -51,6 +51,11 @@ struct aa_sk_ctx {
 	struct aa_label *peer;
 };
 
+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 4ba6db93e5b0..255d2e40386f 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1291,7 +1291,7 @@ static int apparmor_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 {
 	struct aa_sk_ctx *ctx = aa_sock(sk);
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return 0;
 
 	/*
@@ -1407,7 +1407,7 @@ static int apparmor_inet_conn_request(const struct sock *sk, struct sk_buff *skb
 {
 	struct aa_sk_ctx *ctx = aa_sock(sk);
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return 0;
 
 	return apparmor_secmark_check(ctx->label, OP_CONNECT, AA_MAY_CONNECT,
@@ -1423,6 +1423,7 @@ 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 = {
@@ -2085,7 +2086,7 @@ static unsigned int apparmor_ip_postroute(void *priv,
 	struct aa_sk_ctx *ctx;
 	struct sock *sk;
 
-	if (!skb->secmark)
+	if (!aa_secmark() || !skb->secmark)
 		return NF_ACCEPT;
 
 	sk = skb_to_full_sk(skb);
diff --git a/security/lsm_init.c b/security/lsm_init.c
index 54166688efff..4e3944c68bc8 100644
--- a/security/lsm_init.c
+++ b/security/lsm_init.c
@@ -313,6 +313,12 @@ static void __init lsm_prep_single(struct lsm_info *lsm)
 	lsm_blob_size_update(&blobs->lbs_xattr_count,
 			     &blob_sizes.lbs_xattr_count);
 	lsm_blob_size_update(&blobs->lbs_bdev, &blob_sizes.lbs_bdev);
+	if (blobs->lbs_secmark) {
+		if (blob_sizes.lbs_secmark)
+			blobs->lbs_secmark = false;
+		else
+			blob_sizes.lbs_secmark = true;
+	}
 }
 
 /**
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9f816e25198a..18ab1f13f3f9 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -165,7 +165,8 @@ __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));
 }
 
@@ -7160,6 +7161,7 @@ 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 709e0d6cd5e1..2f7b8d79b69f 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -389,6 +389,11 @@ 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 d363adead435..c8c173bb9cc3 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 17ba578b1308..1dcaba0d224a 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 = {
 
 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");
-- 
2.47.0