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Message-ID: <20251001215643.31465-2-casey@schaufler-ca.com>
Date: Wed, 1 Oct 2025 14:56:42 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: casey@...aufler-ca.com,
paul@...l-moore.com,
linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org,
serge@...lyn.com,
keescook@...omium.org,
john.johansen@...onical.com,
penguin-kernel@...ove.sakura.ne.jp,
stephen.smalley.work@...il.com,
linux-kernel@...r.kernel.org,
selinux@...r.kernel.org
Subject: [PATCH 1/2] LSM: Exclusive secmark usage
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@...aufler-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
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