[PATCH] ipv4: tcp: security_sk_alloc() needed for unicast_sock

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

commit be9f4a44e7d41cee (ipv4: tcp: remove per net tcp_sock) added a
selinux regression, reported and bisected by John Stultz

selinux_ip_postroute_compat() expect to find a valid sk->sk_security
pointer, but this field is NULL for unicast_sock

Fix this by adding a new 'kernel' parameter to security_sk_alloc(),
set to true if socket might already have a valid sk->sk_security
pointer. ip_send_unicast_reply() uses a percpu fake socket, so the first
call to security_sk_alloc() will populate sk->sk_security pointer,
subsequent ones will reuse existing context.

Reported-by: John Stultz <johnstul@us.ibm.com>
Bisected-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Eric Paris <eparis@parisplace.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
---
 include/linux/security.h   |    6 +++---
 net/core/sock.c            |    2 +-
 net/ipv4/ip_output.c       |    4 +++-
 security/security.c        |    4 ++--
 security/selinux/hooks.c   |    5 ++++-
 security/smack/smack_lsm.c |   10 ++++++++--
 6 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 4e5a73c..4d8e454 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1601,7 +1601,7 @@ struct security_operations {
 	int (*socket_sock_rcv_skb) (struct sock *sk, struct sk_buff *skb);
 	int (*socket_getpeersec_stream) (struct socket *sock, char __user *optval, int __user *optlen, unsigned len);
 	int (*socket_getpeersec_dgram) (struct socket *sock, struct sk_buff *skb, u32 *secid);
-	int (*sk_alloc_security) (struct sock *sk, int family, gfp_t priority);
+	int (*sk_alloc_security) (struct sock *sk, int family, gfp_t priority, bool kernel);
 	void (*sk_free_security) (struct sock *sk);
 	void (*sk_clone_security) (const struct sock *sk, struct sock *newsk);
 	void (*sk_getsecid) (struct sock *sk, u32 *secid);
@@ -2539,7 +2539,7 @@ int security_sock_rcv_skb(struct sock *sk, struct sk_buff *skb);
 int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
 				      int __user *optlen, unsigned len);
 int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid);
-int security_sk_alloc(struct sock *sk, int family, gfp_t priority);
+int security_sk_alloc(struct sock *sk, int family, gfp_t priority, bool kernel);
 void security_sk_free(struct sock *sk);
 void security_sk_clone(const struct sock *sk, struct sock *newsk);
 void security_sk_classify_flow(struct sock *sk, struct flowi *fl);
@@ -2667,7 +2667,7 @@ static inline int security_socket_getpeersec_dgram(struct socket *sock, struct s
 	return -ENOPROTOOPT;
 }
 
-static inline int security_sk_alloc(struct sock *sk, int family, gfp_t priority)
+static inline int security_sk_alloc(struct sock *sk, int family, gfp_t priority, bool kernel)
 {
 	return 0;
 }
diff --git a/net/core/sock.c b/net/core/sock.c
index 8f67ced..e00cadf 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1186,7 +1186,7 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
 	if (sk != NULL) {
 		kmemcheck_annotate_bitfield(sk, flags);
 
-		if (security_sk_alloc(sk, family, priority))
+		if (security_sk_alloc(sk, family, priority, false))
 			goto out_free;
 
 		if (!try_module_get(prot->owner))
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 76dde25..b233d6e 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1524,6 +1524,8 @@ void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,
 	sk->sk_priority = skb->priority;
 	sk->sk_protocol = ip_hdr(skb)->protocol;
 	sk->sk_bound_dev_if = arg->bound_dev_if;
+	if (security_sk_alloc(sk, PF_INET, GFP_ATOMIC, true))
+		goto out;
 	sock_net_set(sk, net);
 	__skb_queue_head_init(&sk->sk_write_queue);
 	sk->sk_sndbuf = sysctl_wmem_default;
@@ -1539,7 +1541,7 @@ void ip_send_unicast_reply(struct net *net, struct sk_buff *skb, __be32 daddr,
 		skb_set_queue_mapping(nskb, skb_get_queue_mapping(skb));
 		ip_push_pending_frames(sk, &fl4);
 	}
-
+out:
 	put_cpu_var(unicast_sock);
 
 	ip_rt_put(rt);
diff --git a/security/security.c b/security/security.c
index 860aeb3..23cf297 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1146,9 +1146,9 @@ int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u
 }
 EXPORT_SYMBOL(security_socket_getpeersec_dgram);
 
-int security_sk_alloc(struct sock *sk, int family, gfp_t priority)
+int security_sk_alloc(struct sock *sk, int family, gfp_t priority, bool kernel)
 {
-	return security_ops->sk_alloc_security(sk, family, priority);
+	return security_ops->sk_alloc_security(sk, family, priority, kernel);
 }
 
 void security_sk_free(struct sock *sk)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6c77f63..ccd4374 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4289,10 +4289,13 @@ out:
 	return 0;
 }
 
-static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority)
+static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority, bool kernel)
 {
 	struct sk_security_struct *sksec;
 
+	if (kernel && sk->sk_security)
+		return 0;
+
 	sksec = kzalloc(sizeof(*sksec), priority);
 	if (!sksec)
 		return -ENOMEM;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 8221514..0b066d0 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1749,20 +1749,26 @@ static void smack_task_to_inode(struct task_struct *p, struct inode *inode)
  * @sk: the socket
  * @family: unused
  * @gfp_flags: memory allocation flags
+ * @kernel: true if we should check sk_security being already set
  *
  * Assign Smack pointers to current
  *
  * Returns 0 on success, -ENOMEM is there's no memory
  */
-static int smack_sk_alloc_security(struct sock *sk, int family, gfp_t gfp_flags)
+static int smack_sk_alloc_security(struct sock *sk, int family, gfp_t gfp_flags, bool kernel)
 {
-	char *csp = smk_of_current();
+	char *csp;
 	struct socket_smack *ssp;
 
+	if (kernel && sk->sk_security)
+		return 0;
+
 	ssp = kzalloc(sizeof(struct socket_smack), gfp_flags);
 	if (ssp == NULL)
 		return -ENOMEM;
 
+	csp = kernel ? smack_net_ambient : smk_of_current();
+
 	ssp->smk_in = csp;
 	ssp->smk_out = csp;
 	ssp->smk_packet = NULL;