[PATCH net-2.6.25] Add packet filtering based on process's security context.

[PATCH net-2.6.25] Add packet filtering based on process's security context.

[Tetsuo Handa]

Hello.

This is a repost of a patch submitted at http://lkml.org/lkml/2007/11/19/545 .

Current status is that I'm waiting for Samir Bellabes's answer
whether we can handle the following example without this patch.

Tetsuo Handa wrote:
> Hello.
> 
> Samir Bellabes wrote:
> > >> what differences between you approach and netfilter in this case ? if
> > >> it's about packet filtering, you already have all you wishes in
> > >> netfilter project.
> > > Except a hook for making decision with the name of process who picks that packet up known.
> > 
> > I think that we really don't need it, because we can catch the
> > informations as I explained.
> 
> Well, I haven't understood yet why we don't need it.
> 
> How can you know the the name of process who copies that datagram to its userspace memory?
> A socket may be shared by multiple different executable files,
> so the name of the executable file is not known until
> one of processes who share the socket issues accept()/recvmsg() syscall.
> 
> Are you saying that I should not use the name of the executable file?
> 
> Regards.
> 

Tetsuo Handa wrote:
> Hello.
> 
> I made an example.
> 
> Usage:
> 
>   Compile app1 and app2 and run /tmp/app1 .
> 
>   Run something like
>    curl http://localhost:10000/
>   to connect to /tmp/app1.
> 
> I want to know that */tmp/app2* accepts TCP connection
> so that the user can control
> whether this TCP connection from 127.0.0.1 port N
> should be accepted by */tmp/app2* or not.
> 
> How can we do this without socket_post_accept() change?
> 
> Regards.
> 
> ---------- app1.c start ----------
> /* gcc -Wall -O2 -o /tmp/app1 app1.c */
> #include <fcntl.h>
> #include <netinet/in.h>
> #include <stdio.h>
> #include <string.h>
> #include <sys/select.h>
> #include <sys/socket.h>
> #include <sys/types.h>
> #include <unistd.h>
> 
> int main(int argc, char *argv[]) {
> 	const int fd = socket(PF_INET, SOCK_STREAM, 0);
> 	struct sockaddr_in addr;
> 	char buf[16];
> 	memset(&addr, 0, sizeof(addr));
> 	addr.sin_family = AF_INET;
> 	addr.sin_addr.s_addr = htonl(INADDR_ANY);
> 	addr.sin_port = htons(10000);
> 	fprintf(stderr, "%s started.\n", argv[0]);
> 	if (bind(fd, (struct sockaddr *) &addr, sizeof(addr))) {
> 		fprintf(stderr, "Can't bind()\n");
> 		return 1;
> 	} else if (listen(fd, 5)) {
> 		fprintf(stderr, "Can't listen()\n");
> 		return 1;
> 	}
> 	while (1) {
> 		fd_set rfds;
> 		FD_ZERO(&rfds);
> 		FD_SET(fd, &rfds);
> 		select(fd + 1, &rfds, NULL, NULL, NULL);
> 		if (FD_ISSET(fd, &rfds)) break;
> 		fprintf(stderr, "Can't select()\n");
> 		return 1;
> 	}
> 	if (fcntl(fd, FD_CLOEXEC, 0)) {
> 		fprintf(stderr, "Can't fcntl()\n");
> 		return 1;
> 	}
> 	snprintf(buf, sizeof(buf), "%d", fd);
> 	execlp("/tmp/app2", "app2", buf, NULL);
> 	fprintf(stderr, "Can't execve()\n");
> 	return 1;
> }
> ---------- app1.c end ----------
> 
> ---------- app2.c start ----------
> /* gcc -Wall -O2 -o /tmp/app2 app2.c */
> #include <netinet/in.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/socket.h>
> #include <sys/types.h>
> #include <unistd.h>
> 
> int main(int argc, char *argv[]) {
> 	int lfd;
> 	if (argc != 2) {
> 		fprintf(stderr, "Bad parameter.\n");
> 		return 1;
> 	}
> 	fprintf(stderr, "%s started.\n", argv[0]);
> 	lfd = atoi(argv[1]);
> 	while (1) {
> 		struct sockaddr_in addr;
> 		socklen_t size = sizeof(addr);
> 		int fd = accept(lfd, (struct sockaddr *) &addr, &size);
> 		char c;
> 		if (fd == EOF) {
> 			fprintf(stderr, "Can't accept()\n");
> 			return 1;
> 		}
> 		while (read(fd, &c, 1) == 1 && write(fd, &c, 1) == 1);
> 		close(fd);
> 	}
> 	return 0;
> }
> ---------- app2.c end ----------
> 

Regards.
----------
Subject: Add packet filtering based on process's security context.

This patch allows LSM modules filter incoming connections/datagrams
based on the process's security context who is attempting to pick up.

There are already hooks to filter incoming connections/datagrams
based on the socket's security context, but these hooks are not
applicable when one wants to do TCP Wrapper-like filtering
(e.g. App1 is permitted to accept TCP connections from 192.168.0.0/16).

Precautions: This approach has a side effect which unlikely occurs.

If a socket is shared by multiple processes with differnt policy,
the process who should be able to accept this connection
will not be able to accept this connection
because socket_post_accept() aborts this connection.
But if socket_post_accept() doesn't abort this connection,
the process who must not be able to accept this connection
will repeat accept() forever, which is a worse side effect.

Similarly, if a socket is shared by multiple processes with differnt policy,
the process who should be able to pick up this datagram
will not be able to pick up this datagram
because socket_post_recv_datagram() discards this datagram.
But if socket_post_recv_datagram() doesn't discard this datagram,
the process who must not be able to pick up this datagram
will repeat recvmsg() forever, which is a worse side effect.

So, don't give different permissions between processes who shares one socket.
Otherwise, some connections/datagrams cannot be delivered to intended process.

Signed-off-by: Kentaro Takeda <takedakn@nttdata.co.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 include/linux/security.h |   34 +++++++++++++++++++++++++++++-----
 net/core/datagram.c      |   29 ++++++++++++++++++++++++++++-
 net/socket.c             |    7 +++++--
 security/dummy.c         |   13 ++++++++++---
 security/security.c      |   10 ++++++++--
 5 files changed, 80 insertions(+), 13 deletions(-)

--- net-2.6.25.orig/include/linux/security.h
+++ net-2.6.25/include/linux/security.h
@@ -781,8 +781,12 @@ struct request_sock;
  * @socket_post_accept:
  *	This hook allows a security module to copy security
  *	information into the newly created socket's inode.
+ *	This hook also allows a security module to filter connections
+ *	from unwanted peers based on the process accepting this connection.
+ *	The connection will be aborted if this hook returns nonzero.
  *	@sock contains the listening socket structure.
  *	@newsock contains the newly created server socket for connection.
+ *	Return 0 if permission is granted.
  * @socket_sendmsg:
  *	Check permission before transmitting a message to another socket.
  *	@sock contains the socket structure.
@@ -796,6 +800,15 @@ struct request_sock;
  *	@size contains the size of message structure.
  *	@flags contains the operational flags.
  *	Return 0 if permission is granted.  
+ * @socket_post_recv_datagram:
+ *	Check permission after receiving a datagram.
+ *	This hook allows a security module to filter packets
+ *	from unwanted peers based on the process receiving this datagram.
+ *	The packet will be discarded if this hook returns nonzero.
+ *	@sk contains the socket.
+ *	@skb contains the socket buffer.
+ *	@flags contains the operational flags.
+ *	Return 0 if permission is granted.
  * @socket_getsockname:
  *	Check permission before the local address (name) of the socket object
  *	@sock is retrieved.
@@ -1387,12 +1400,13 @@ struct security_operations {
 			       struct sockaddr * address, int addrlen);
 	int (*socket_listen) (struct socket * sock, int backlog);
 	int (*socket_accept) (struct socket * sock, struct socket * newsock);
-	void (*socket_post_accept) (struct socket * sock,
-				    struct socket * newsock);
+	int (*socket_post_accept) (struct socket *sock, struct socket *newsock);
 	int (*socket_sendmsg) (struct socket * sock,
 			       struct msghdr * msg, int size);
 	int (*socket_recvmsg) (struct socket * sock,
 			       struct msghdr * msg, int size, int flags);
+	int (*socket_post_recv_datagram) (struct sock *sk, struct sk_buff *skb,
+					  unsigned int flags);
 	int (*socket_getsockname) (struct socket * sock);
 	int (*socket_getpeername) (struct socket * sock);
 	int (*socket_getsockopt) (struct socket * sock, int level, int optname);
@@ -2297,10 +2311,12 @@ int security_socket_bind(struct socket *
 int security_socket_connect(struct socket *sock, struct sockaddr *address, int addrlen);
 int security_socket_listen(struct socket *sock, int backlog);
 int security_socket_accept(struct socket *sock, struct socket *newsock);
-void security_socket_post_accept(struct socket *sock, struct socket *newsock);
+int security_socket_post_accept(struct socket *sock, struct socket *newsock);
 int security_socket_sendmsg(struct socket *sock, struct msghdr *msg, int size);
 int security_socket_recvmsg(struct socket *sock, struct msghdr *msg,
 			    int size, int flags);
+int security_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+				       unsigned int flags);
 int security_socket_getsockname(struct socket *sock);
 int security_socket_getpeername(struct socket *sock);
 int security_socket_getsockopt(struct socket *sock, int level, int optname);
@@ -2376,9 +2392,10 @@ static inline int security_socket_accept
 	return 0;
 }
 
-static inline void security_socket_post_accept(struct socket * sock, 
-					       struct socket * newsock)
+static inline int security_socket_post_accept(struct socket *sock,
+					      struct socket *newsock)
 {
+	return 0;
 }
 
 static inline int security_socket_sendmsg(struct socket * sock, 
@@ -2394,6 +2411,13 @@ static inline int security_socket_recvms
 	return 0;
 }
 
+static inline int security_socket_post_recv_datagram(struct sock *sk,
+						     struct sk_buff *skb,
+						     unsigned int flags)
+{
+	return 0;
+}
+
 static inline int security_socket_getsockname(struct socket * sock)
 {
 	return 0;
--- net-2.6.25.orig/net/socket.c
+++ net-2.6.25/net/socket.c
@@ -1454,13 +1454,16 @@ asmlinkage long sys_accept(int fd, struc
 			goto out_fd;
 	}
 
+	/* Filter connections from unwanted peers. */
+	err = security_socket_post_accept(sock, newsock);
+	if (err)
+		goto out_fd;
+
 	/* File flags are not inherited via accept() unlike another OSes. */
 
 	fd_install(newfd, newfile);
 	err = newfd;
 
-	security_socket_post_accept(sock, newsock);
-
 out_put:
 	fput_light(sock->file, fput_needed);
 out:
--- net-2.6.25.orig/security/dummy.c
+++ net-2.6.25/security/dummy.c
@@ -748,10 +748,10 @@ static int dummy_socket_accept (struct s
 	return 0;
 }
 
-static void dummy_socket_post_accept (struct socket *sock, 
-				      struct socket *newsock)
+static int dummy_socket_post_accept(struct socket *sock,
+				    struct socket *newsock)
 {
-	return;
+	return 0;
 }
 
 static int dummy_socket_sendmsg (struct socket *sock, struct msghdr *msg,
@@ -766,6 +766,12 @@ static int dummy_socket_recvmsg (struct 
 	return 0;
 }
 
+static int dummy_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+					   unsigned int flags)
+{
+	return 0;
+}
+
 static int dummy_socket_getsockname (struct socket *sock)
 {
 	return 0;
@@ -1099,6 +1105,7 @@ void security_fixup_ops (struct security
 	set_to_dummy_if_null(ops, socket_post_accept);
 	set_to_dummy_if_null(ops, socket_sendmsg);
 	set_to_dummy_if_null(ops, socket_recvmsg);
+	set_to_dummy_if_null(ops, socket_post_recv_datagram);
 	set_to_dummy_if_null(ops, socket_getsockname);
 	set_to_dummy_if_null(ops, socket_getpeername);
 	set_to_dummy_if_null(ops, socket_setsockopt);
--- net-2.6.25.orig/net/core/datagram.c
+++ net-2.6.25/net/core/datagram.c
@@ -55,6 +55,7 @@
 #include <net/checksum.h>
 #include <net/sock.h>
 #include <net/tcp_states.h>
+#include <linux/security.h>
 
 /*
  *	Is a socket 'connection oriented' ?
@@ -148,6 +149,7 @@ struct sk_buff *__skb_recv_datagram(stru
 {
 	struct sk_buff *skb;
 	long timeo;
+	unsigned long cpu_flags;
 	/*
 	 * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
 	 */
@@ -165,7 +167,6 @@ struct sk_buff *__skb_recv_datagram(stru
 		 * Look at current nfs client by the way...
 		 * However, this function was corrent in any case. 8)
 		 */
-		unsigned long cpu_flags;
 
 		spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
 		skb = skb_peek(&sk->sk_receive_queue);
@@ -179,6 +180,14 @@ struct sk_buff *__skb_recv_datagram(stru
 		}
 		spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
 
+		/* Filter packets from unwanted peers. */
+		if (skb) {
+			error = security_socket_post_recv_datagram(sk, skb,
+								   flags);
+			if (error)
+				goto force_dequeue;
+		}
+
 		if (skb)
 			return skb;
 
@@ -191,6 +200,24 @@ struct sk_buff *__skb_recv_datagram(stru
 
 	return NULL;
 
+force_dequeue:
+	/* Drop this packet because LSM says "Don't pass it to the caller". */
+	if (!(flags & MSG_PEEK))
+		goto no_peek;
+	/*
+	 * If this packet is MSG_PEEK'ed, dequeue it forcibly
+	 * so that this packet won't prevent the caller from picking up
+	 * next packet.
+	 */
+	spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
+	if (skb == skb_peek(&sk->sk_receive_queue)) {
+		__skb_unlink(skb, &sk->sk_receive_queue);
+		atomic_dec(&skb->users);
+		/* Do I have something to do with skb->peeked ? */
+	}
+	spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
+no_peek:
+	kfree_skb(skb);
 no_packet:
 	*err = error;
 	return NULL;
--- net-2.6.25.orig/security/security.c
+++ net-2.6.25/security/security.c
@@ -869,9 +869,9 @@ int security_socket_accept(struct socket
 	return security_ops->socket_accept(sock, newsock);
 }
 
-void security_socket_post_accept(struct socket *sock, struct socket *newsock)
+int security_socket_post_accept(struct socket *sock, struct socket *newsock)
 {
-	security_ops->socket_post_accept(sock, newsock);
+	return security_ops->socket_post_accept(sock, newsock);
 }
 
 int security_socket_sendmsg(struct socket *sock, struct msghdr *msg, int size)
@@ -885,6 +885,12 @@ int security_socket_recvmsg(struct socke
 	return security_ops->socket_recvmsg(sock, msg, size, flags);
 }
 
+int security_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+				       unsigned int flags)
+{
+	return security_ops->socket_post_recv_datagram(sk, skb, flags);
+}
+
 int security_socket_getsockname(struct socket *sock)
 {
 	return security_ops->socket_getsockname(sock);

Re: [PATCH net-2.6.25] Add packet filtering based on process\'s security context.

[Tetsuo Handa]

Hello.

Casey Schaufler wrote:
> Do you have a real situation where two user processes with different
> security contexts share a socket? How do you get into that situation,
> and is it appropriate to have that situation in your security scheme?
> Can this occur without using privilege?

I hope such situation won't occur, as I have mentioned in the previous
posting.

| Precautions: This approach has a side effect which unlikely occurs.
| 
| If a socket is shared by multiple processes with differnt policy,
| the process who should be able to accept this connection
| will not be able to accept this connection
| because socket_post_accept() aborts this connection.
| But if socket_post_accept() doesn't abort this connection,
| the process who must not be able to accept this connection
| will repeat accept() forever, which is a worse side effect.
| 
| Similarly, if a socket is shared by multiple processes with differnt policy,
| the process who should be able to pick up this datagram
| will not be able to pick up this datagram
| because socket_post_recv_datagram() discards this datagram.
| But if socket_post_recv_datagram() doesn't discard this datagram,
| the process who must not be able to pick up this datagram
| will repeat recvmsg() forever, which is a worse side effect.
| 
| So, don't give different permissions between processes who shares one socket.
| Otherwise, some connections/datagrams cannot be delivered to intended process.

But it is possible to write a code like

---------- app3.c start ----------
/* gcc -Wall -O2 -o /tmp/app3 app3.c */
#include <fcntl.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
	const int fd1 = socket(PF_INET, SOCK_DGRAM, 0), fd2 = socket(PF_INET, SOCK_DGRAM, 0);
	struct sockaddr_in addr;
	char buf[16];
	memset(&addr, 0, sizeof(addr));
	addr.sin_family = AF_INET;
	addr.sin_addr.s_addr = htonl(INADDR_ANY);
	addr.sin_port = htons(10000);
	fprintf(stderr, "%s started.\n", argv[0]);
	if (bind(fd1, (struct sockaddr *) &addr, sizeof(addr))) {
		fprintf(stderr, "Can't bind()\n");
		return 1;
	}
	if (sendto(fd2, "hello\n", 6, 0, (struct sockaddr *) &addr, sizeof(addr)) != 6 ||
	    sendto(fd2, "world\n", 6, 0, (struct sockaddr *) &addr, sizeof(addr)) != 6) {
		fprintf(stderr, "Can't sendto()\n");
		return 1;
	}
	while (1) {
		fd_set rfds;
		FD_ZERO(&rfds);
		FD_SET(fd1, &rfds);
		select(fd1 + 1, &rfds, NULL, NULL, NULL);
		if (FD_ISSET(fd1, &rfds)) break;
		fprintf(stderr, "Can't select()\n");
		return 1;
	}
	if (fcntl(fd1, FD_CLOEXEC, 0)) {
		fprintf(stderr, "Can't fcntl()\n");
		return 1;
	}
	snprintf(buf, sizeof(buf), "%d", fd1);
	execlp("/tmp/app4", "app4", buf, NULL);
	fprintf(stderr, "Can't execve()\n");
	return 1;
}
---------- app3.c end ----------

---------- app4.c start ----------
/* gcc -Wall -O2 -o /tmp/app4 app4.c */
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
	int fd;
	if (argc != 2) {
		fprintf(stderr, "Bad parameter.\n");
		return 1;
	}
	fprintf(stderr, "%s started.\n", argv[0]);
	fd = atoi(argv[1]);
	while (1) {
		struct sockaddr_in addr;
		socklen_t size = sizeof(addr);
		char buffer[1024];
		int len;
		len = recvfrom(fd, buffer, sizeof(buffer), 0, (struct sockaddr *) &addr, &size);
		if (len == EOF) {
			fprintf(stderr, "Can't recvfrom()\n");
			return 1;
		}
		write(1, buffer, len);
	}
	return 0;
}
---------- app4.c end ----------

and assign different policy to /tmp/app1 and /tmp/app2 .
Therefore, I want to check at sys_recvmsg() time.

(Usage: Compile app3 and app4 and run /tmp/app3 .)
For TCP's case, see http://www.mail-archive.com/linux-security-module@vger.kernel.org/msg02531.html

What I want to do is perform connection/packet filtering
with the recipient of the incoming connection/packet known.
My security scheme controls based on the recipient of the incoming connection/packet.
In this case, not /tmp/app1 or /tmp/app3 , but /tmp/app2 or /tmp/app4.
This case occurs without using privilege.

Regards.

Re: [PATCH net-2.6.25] Add packet filtering based on process's security context.

[Tetsuo Handa]

Hello.

Are there any remaining questions/problems about this patch?
If none, I want this patch applied to net-2.6.25 tree.

Regards.

---------------
This patch modifies security_socket_post_accept() and introduces
security_socket_post_recv_datagram() LSM hooks.

Currently, security_socket_post_accept() is called *after* fd_install()
at sys_accept(). This means that userland process might access accept()ed
but not yet properly labeled socket.
I believe this security_socket_post_accept() should be called *before*
fd_install() for the three reasons.

 * The userland process will always access proper context labeled by
   security_socket_post_accept() rather than default context labeled by
   security_inode_alloc() (called from alloc_inode() from new_inode() from
   sock_alloc() from sys_accept()). This gives a security module
   a chance to perform access control based on proper context.

 * If security_socket_post_accept() failed to assign proper context
   (e.g. -ENOMEM), the accept()ed socket can't have proper context.
   Use of void for security_socket_post_accept() deprives a security module
   of a chance to abandon the accept()ed socket.

 * A security module can perform connection filtering based on
   process's security context.
   If security_socket_post_accept() is called after fd_install(),
   it is too late to do so because the accept()ed socket is already visible
   to userland processes.


Currently, there is no way to directly map security context from incoming
packet to user process. This is because the creator or owner of a socket is
not always the receiver of an incoming packet. The userland process who
receives the incoming packet is not known until a process calls sys_recvmsg().
So, I want to add a LSM hook to give a security module a chance to control
after the recipient of the incoming packet is known.

Signed-off-by: Kentaro Takeda <takedakn@nttdata.co.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 include/linux/security.h |   34 +++++++++++++++++++++++++++++-----
 net/core/datagram.c      |   29 ++++++++++++++++++++++++++++-
 net/socket.c             |    7 +++++--
 security/dummy.c         |   13 ++++++++++---
 security/security.c      |   10 ++++++++--
 5 files changed, 80 insertions(+), 13 deletions(-)

--- net-2.6.25.orig/include/linux/security.h
+++ net-2.6.25/include/linux/security.h
@@ -781,8 +781,12 @@ struct request_sock;
  * @socket_post_accept:
  *	This hook allows a security module to copy security
  *	information into the newly created socket's inode.
+ *	This hook also allows a security module to filter connections
+ *	from unwanted peers based on the process accepting this connection.
+ *	The connection will be aborted if this hook returns nonzero.
  *	@sock contains the listening socket structure.
  *	@newsock contains the newly created server socket for connection.
+ *	Return 0 if permission is granted.
  * @socket_sendmsg:
  *	Check permission before transmitting a message to another socket.
  *	@sock contains the socket structure.
@@ -796,6 +800,15 @@ struct request_sock;
  *	@size contains the size of message structure.
  *	@flags contains the operational flags.
  *	Return 0 if permission is granted.  
+ * @socket_post_recv_datagram:
+ *	Check permission after receiving a datagram.
+ *	This hook allows a security module to filter packets
+ *	from unwanted peers based on the process receiving this datagram.
+ *	The packet will be discarded if this hook returns nonzero.
+ *	@sk contains the socket.
+ *	@skb contains the socket buffer.
+ *	@flags contains the operational flags.
+ *	Return 0 if permission is granted.
  * @socket_getsockname:
  *	Check permission before the local address (name) of the socket object
  *	@sock is retrieved.
@@ -1387,12 +1400,13 @@ struct security_operations {
 			       struct sockaddr * address, int addrlen);
 	int (*socket_listen) (struct socket * sock, int backlog);
 	int (*socket_accept) (struct socket * sock, struct socket * newsock);
-	void (*socket_post_accept) (struct socket * sock,
-				    struct socket * newsock);
+	int (*socket_post_accept) (struct socket *sock, struct socket *newsock);
 	int (*socket_sendmsg) (struct socket * sock,
 			       struct msghdr * msg, int size);
 	int (*socket_recvmsg) (struct socket * sock,
 			       struct msghdr * msg, int size, int flags);
+	int (*socket_post_recv_datagram) (struct sock *sk, struct sk_buff *skb,
+					  unsigned int flags);
 	int (*socket_getsockname) (struct socket * sock);
 	int (*socket_getpeername) (struct socket * sock);
 	int (*socket_getsockopt) (struct socket * sock, int level, int optname);
@@ -2297,10 +2311,12 @@ int security_socket_bind(struct socket *
 int security_socket_connect(struct socket *sock, struct sockaddr *address, int addrlen);
 int security_socket_listen(struct socket *sock, int backlog);
 int security_socket_accept(struct socket *sock, struct socket *newsock);
-void security_socket_post_accept(struct socket *sock, struct socket *newsock);
+int security_socket_post_accept(struct socket *sock, struct socket *newsock);
 int security_socket_sendmsg(struct socket *sock, struct msghdr *msg, int size);
 int security_socket_recvmsg(struct socket *sock, struct msghdr *msg,
 			    int size, int flags);
+int security_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+				       unsigned int flags);
 int security_socket_getsockname(struct socket *sock);
 int security_socket_getpeername(struct socket *sock);
 int security_socket_getsockopt(struct socket *sock, int level, int optname);
@@ -2376,9 +2392,10 @@ static inline int security_socket_accept
 	return 0;
 }
 
-static inline void security_socket_post_accept(struct socket * sock, 
-					       struct socket * newsock)
+static inline int security_socket_post_accept(struct socket *sock,
+					      struct socket *newsock)
 {
+	return 0;
 }
 
 static inline int security_socket_sendmsg(struct socket * sock, 
@@ -2394,6 +2411,13 @@ static inline int security_socket_recvms
 	return 0;
 }
 
+static inline int security_socket_post_recv_datagram(struct sock *sk,
+						     struct sk_buff *skb,
+						     unsigned int flags)
+{
+	return 0;
+}
+
 static inline int security_socket_getsockname(struct socket * sock)
 {
 	return 0;
--- net-2.6.25.orig/net/socket.c
+++ net-2.6.25/net/socket.c
@@ -1454,13 +1454,16 @@ asmlinkage long sys_accept(int fd, struc
 			goto out_fd;
 	}
 
+	/* Filter connections from unwanted peers. */
+	err = security_socket_post_accept(sock, newsock);
+	if (err)
+		goto out_fd;
+
 	/* File flags are not inherited via accept() unlike another OSes. */
 
 	fd_install(newfd, newfile);
 	err = newfd;
 
-	security_socket_post_accept(sock, newsock);
-
 out_put:
 	fput_light(sock->file, fput_needed);
 out:
--- net-2.6.25.orig/security/dummy.c
+++ net-2.6.25/security/dummy.c
@@ -748,10 +748,10 @@ static int dummy_socket_accept (struct s
 	return 0;
 }
 
-static void dummy_socket_post_accept (struct socket *sock, 
-				      struct socket *newsock)
+static int dummy_socket_post_accept(struct socket *sock,
+				    struct socket *newsock)
 {
-	return;
+	return 0;
 }
 
 static int dummy_socket_sendmsg (struct socket *sock, struct msghdr *msg,
@@ -766,6 +766,12 @@ static int dummy_socket_recvmsg (struct 
 	return 0;
 }
 
+static int dummy_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+					   unsigned int flags)
+{
+	return 0;
+}
+
 static int dummy_socket_getsockname (struct socket *sock)
 {
 	return 0;
@@ -1099,6 +1105,7 @@ void security_fixup_ops (struct security
 	set_to_dummy_if_null(ops, socket_post_accept);
 	set_to_dummy_if_null(ops, socket_sendmsg);
 	set_to_dummy_if_null(ops, socket_recvmsg);
+	set_to_dummy_if_null(ops, socket_post_recv_datagram);
 	set_to_dummy_if_null(ops, socket_getsockname);
 	set_to_dummy_if_null(ops, socket_getpeername);
 	set_to_dummy_if_null(ops, socket_setsockopt);
--- net-2.6.25.orig/net/core/datagram.c
+++ net-2.6.25/net/core/datagram.c
@@ -55,6 +55,7 @@
 #include <net/checksum.h>
 #include <net/sock.h>
 #include <net/tcp_states.h>
+#include <linux/security.h>
 
 /*
  *	Is a socket 'connection oriented' ?
@@ -148,6 +149,7 @@ struct sk_buff *__skb_recv_datagram(stru
 {
 	struct sk_buff *skb;
 	long timeo;
+	unsigned long cpu_flags;
 	/*
 	 * Caller is allowed not to check sk->sk_err before skb_recv_datagram()
 	 */
@@ -165,7 +167,6 @@ struct sk_buff *__skb_recv_datagram(stru
 		 * Look at current nfs client by the way...
 		 * However, this function was corrent in any case. 8)
 		 */
-		unsigned long cpu_flags;
 
 		spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
 		skb = skb_peek(&sk->sk_receive_queue);
@@ -179,6 +180,14 @@ struct sk_buff *__skb_recv_datagram(stru
 		}
 		spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
 
+		/* Filter packets from unwanted peers. */
+		if (skb) {
+			error = security_socket_post_recv_datagram(sk, skb,
+								   flags);
+			if (error)
+				goto force_dequeue;
+		}
+
 		if (skb)
 			return skb;
 
@@ -191,6 +200,24 @@ struct sk_buff *__skb_recv_datagram(stru
 
 	return NULL;
 
+force_dequeue:
+	/* Drop this packet because LSM says "Don't pass it to the caller". */
+	if (!(flags & MSG_PEEK))
+		goto no_peek;
+	/*
+	 * If this packet is MSG_PEEK'ed, dequeue it forcibly
+	 * so that this packet won't prevent the caller from picking up
+	 * next packet.
+	 */
+	spin_lock_irqsave(&sk->sk_receive_queue.lock, cpu_flags);
+	if (skb == skb_peek(&sk->sk_receive_queue)) {
+		__skb_unlink(skb, &sk->sk_receive_queue);
+		atomic_dec(&skb->users);
+		/* Do I have something to do with skb->peeked ? */
+	}
+	spin_unlock_irqrestore(&sk->sk_receive_queue.lock, cpu_flags);
+no_peek:
+	kfree_skb(skb);
 no_packet:
 	*err = error;
 	return NULL;
--- net-2.6.25.orig/security/security.c
+++ net-2.6.25/security/security.c
@@ -869,9 +869,9 @@ int security_socket_accept(struct socket
 	return security_ops->socket_accept(sock, newsock);
 }
 
-void security_socket_post_accept(struct socket *sock, struct socket *newsock)
+int security_socket_post_accept(struct socket *sock, struct socket *newsock)
 {
-	security_ops->socket_post_accept(sock, newsock);
+	return security_ops->socket_post_accept(sock, newsock);
 }
 
 int security_socket_sendmsg(struct socket *sock, struct msghdr *msg, int size)
@@ -885,6 +885,12 @@ int security_socket_recvmsg(struct socke
 	return security_ops->socket_recvmsg(sock, msg, size, flags);
 }
 
+int security_socket_post_recv_datagram(struct sock *sk, struct sk_buff *skb,
+				       unsigned int flags)
+{
+	return security_ops->socket_post_recv_datagram(sk, skb, flags);
+}
+
 int security_socket_getsockname(struct socket *sock)
 {
 	return security_ops->socket_getsockname(sock);

Re: [PATCH net-2.6.25] Add packet filtering based on process's security context.

[Paul Moore]

On Thursday 24 January 2008 6:47:55 am Tetsuo Handa wrote:
> Are there any remaining questions/problems about this patch?
> If none, I want this patch applied to net-2.6.25 tree.

Hello,

Taking into consideration that there are no current in-tree users of 
this patch and the only known user of this functionality is TOMOYO, 
which is still dealing with some unresolved VFS issues, I suggest not 
merging this patch at the current time.  My recommendation is to 
continue to work on resolving the VFS issues (which it appears you are 
working on) and then submitting all of the required TOMOYO changes at 
once.

As a general rule, removing functionality from the kernel tends to be 
much more difficult then adding it.

-- 
paul moore
linux security @ hp