[AF_UNIX]: Datagram getpeersec

This patch implements an API whereby an application can determine the
label of its peer's Unix datagram sockets via the auxiliary data mechanism of
recvmsg.

Patch purpose:

This patch enables a security-aware application to retrieve the
security context of the peer of a Unix datagram socket.  The application
can then use this security context to determine the security context for
processing on behalf of the peer who sent the packet.

Patch design and implementation:

The design and implementation is very similar to the UDP case for INET
sockets.  Basically we build upon the existing Unix domain socket API for
retrieving user credentials.  Linux offers the API for obtaining user
credentials via ancillary messages (i.e., out of band/control messages
that are bundled together with a normal message).  To retrieve the security
context, the application first indicates to the kernel such desire by
setting the SO_PASSSEC option via getsockopt.  Then the application
retrieves the security context using the auxiliary data mechanism.

An example server application for Unix datagram socket should look like this:

toggle = 1;
toggle_len = sizeof(toggle);

setsockopt(sockfd, SOL_SOCKET, SO_PASSSEC, &toggle, &toggle_len);
recvmsg(sockfd, &msg_hdr, 0);
if (msg_hdr.msg_controllen > sizeof(struct cmsghdr)) {
    cmsg_hdr = CMSG_FIRSTHDR(&msg_hdr);
    if (cmsg_hdr->cmsg_len <= CMSG_LEN(sizeof(scontext)) &&
        cmsg_hdr->cmsg_level == SOL_SOCKET &&
        cmsg_hdr->cmsg_type == SCM_SECURITY) {
        memcpy(&scontext, CMSG_DATA(cmsg_hdr), sizeof(scontext));
    }
}

sock_setsockopt is enhanced with a new socket option SOCK_PASSSEC to allow
a server socket to receive security context of the peer.

Testing:

We have tested the patch by setting up Unix datagram client and server
applications.  We verified that the server can retrieve the security context
using the auxiliary data mechanism of recvmsg.

Signed-off-by: Catherine Zhang <cxzhang@watson.ibm.com>
Acked-by: Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/asm-alpha/socket.h

@@ -51,6 +51,7 @@
 #define SCM_TIMESTAMP		SO_TIMESTAMP
 
 #define SO_PEERSEC		30
+#define SO_PASSSEC		34
 
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		19

include/asm-arm/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-arm26/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-cris/socket.h

@@ -50,6 +50,7 @@
 #define SO_ACCEPTCONN          30
 
 #define SO_PEERSEC             31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */
 

include/asm-frv/socket.h

@@ -48,6 +48,7 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */
 

include/asm-h8300/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-i386/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-ia64/socket.h

@@ -57,5 +57,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC             31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_IA64_SOCKET_H */

include/asm-m32r/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_M32R_SOCKET_H */

include/asm-m68k/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC             31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-mips/socket.h

@@ -69,6 +69,7 @@ To add: #define SO_REUSEPORT 0x0200	/* Allow local address and port reuse.  */
 #define SO_PEERSEC		30
 #define SO_SNDBUFFORCE		31
 #define SO_RCVBUFFORCE		33
+#define SO_PASSSEC		34
 
 #ifdef __KERNEL__
 

include/asm-parisc/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		0x401c
 
 #define SO_PEERSEC		0x401d
+#define SO_PASSSEC		0x401e
 
 #endif /* _ASM_SOCKET_H */

include/asm-powerpc/socket.h

@@ -55,5 +55,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif	/* _ASM_POWERPC_SOCKET_H */

include/asm-s390/socket.h

@@ -56,5 +56,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-sh/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* __ASM_SH_SOCKET_H */

include/asm-sparc/socket.h

@@ -48,6 +48,7 @@
 #define SCM_TIMESTAMP		SO_TIMESTAMP
 
 #define SO_PEERSEC		0x001e
+#define SO_PASSSEC		0x001f
 
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		0x5001

include/asm-sparc64/socket.h

@@ -48,6 +48,7 @@
 #define SCM_TIMESTAMP		SO_TIMESTAMP
 
 #define SO_PEERSEC		0x001e
+#define SO_PASSSEC		0x001f
 
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		0x5001

include/asm-v850/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif /* __V850_SOCKET_H__ */

include/asm-x86_64/socket.h

@@ -48,5 +48,6 @@
 #define SO_ACCEPTCONN		30
 
 #define SO_PEERSEC             31
+#define SO_PASSSEC		34
 
 #endif /* _ASM_SOCKET_H */

include/asm-xtensa/socket.h

@@ -59,5 +59,6 @@
 
 #define SO_ACCEPTCONN		30
 #define SO_PEERSEC		31
+#define SO_PASSSEC		34
 
 #endif	/* _XTENSA_SOCKET_H */

include/linux/net.h

@@ -61,6 +61,7 @@ typedef enum {
 #define SOCK_ASYNC_WAITDATA	1
 #define SOCK_NOSPACE		2
 #define SOCK_PASSCRED		3
+#define SOCK_PASSSEC		4
 
 #ifndef ARCH_HAS_SOCKET_TYPES
 /**

include/net/af_unix.h

@@ -53,10 +53,16 @@ struct unix_address {
 struct unix_skb_parms {
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
+#ifdef CONFIG_SECURITY_NETWORK
+	char			*secdata;	/* Security context	*/
+	u32			seclen;		/* Security length	*/
+#endif
 };
 
 #define UNIXCB(skb) 	(*(struct unix_skb_parms*)&((skb)->cb))
 #define UNIXCREDS(skb)	(&UNIXCB((skb)).creds)
+#define UNIXSECDATA(skb)	(&UNIXCB((skb)).secdata)
+#define UNIXSECLEN(skb)		(&UNIXCB((skb)).seclen)
 
 #define unix_state_rlock(s)	spin_lock(&unix_sk(s)->lock)
 #define unix_state_runlock(s)	spin_unlock(&unix_sk(s)->lock)

include/net/scm.h

@@ -19,6 +19,10 @@ struct scm_cookie
 {
 	struct ucred		creds;		/* Skb credentials	*/
 	struct scm_fp_list	*fp;		/* Passed files		*/
+#ifdef CONFIG_SECURITY_NETWORK
+	char			*secdata;	/* Security context	*/
+	u32			seclen;		/* Security length	*/
+#endif
 	unsigned long		seq;		/* Connection seqno	*/
 };
 
@@ -48,6 +52,17 @@ static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
 	return __scm_send(sock, msg, scm);
 }
 
+#ifdef CONFIG_SECURITY_NETWORK
+static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+{
+	if (test_bit(SOCK_PASSSEC, &sock->flags) && scm->secdata != NULL)
+		put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, scm->seclen, scm->secdata);
+}
+#else
+static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
+{ }
+#endif /* CONFIG_SECURITY_NETWORK */
+
 static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 				struct scm_cookie *scm, int flags)
 {
@@ -62,6 +77,8 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 	if (test_bit(SOCK_PASSCRED, &sock->flags))
 		put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(scm->creds), &scm->creds);
 
+	scm_passec(sock, msg, scm);
+
 	if (!scm->fp)
 		return;
 	

net/core/sock.c

@@ -565,6 +565,13 @@ set_rcvbuf:
 			ret = -ENONET;
 			break;
 
+		case SO_PASSSEC:
+			if (valbool)
+				set_bit(SOCK_PASSSEC, &sock->flags);
+			else
+				clear_bit(SOCK_PASSSEC, &sock->flags);
+			break;
+
 		/* We implement the SO_SNDLOWAT etc to
 		   not be settable (1003.1g 5.3) */
 		default:
@@ -723,6 +730,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 			v.val = sk->sk_state == TCP_LISTEN;
 			break;
 
+		case SO_PASSSEC:
+			v.val = test_bit(SOCK_PASSSEC, &sock->flags) ? 1 : 0;
+			break;
+
 		case SO_PEERSEC:
 			return security_socket_getpeersec_stream(sock, optval, optlen, len);
 

net/unix/af_unix.c

@@ -128,6 +128,30 @@ static atomic_t unix_nr_socks = ATOMIC_INIT(0);
 
 #define UNIX_ABSTRACT(sk)	(unix_sk(sk)->addr->hash != UNIX_HASH_SIZE)
 
+#ifdef CONFIG_SECURITY_NETWORK
+static void unix_get_peersec_dgram(struct sk_buff *skb)
+{
+	int err;
+
+	err = security_socket_getpeersec_dgram(skb, UNIXSECDATA(skb),
+					       UNIXSECLEN(skb));
+	if (err)
+		*(UNIXSECDATA(skb)) = NULL;
+}
+
+static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
+{
+	scm->secdata = *UNIXSECDATA(skb);
+	scm->seclen = *UNIXSECLEN(skb);
+}
+#else
+static void unix_get_peersec_dgram(struct sk_buff *skb)
+{ }
+
+static inline void unix_set_secdata(struct scm_cookie *scm, struct sk_buff *skb)
+{ }
+#endif /* CONFIG_SECURITY_NETWORK */
+
 /*
  *  SMP locking strategy:
  *    hash table is protected with spinlock unix_table_lock
@@ -1291,6 +1315,8 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (siocb->scm->fp)
 		unix_attach_fds(siocb->scm, skb);
 
+	unix_get_peersec_dgram(skb);
+
 	skb->h.raw = skb->data;
 	err = memcpy_fromiovec(skb_put(skb,len), msg->msg_iov, len);
 	if (err)
@@ -1570,6 +1596,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
 		memset(&tmp_scm, 0, sizeof(tmp_scm));
 	}
 	siocb->scm->creds = *UNIXCREDS(skb);
+	unix_set_secdata(siocb->scm, skb);
 
 	if (!(flags & MSG_PEEK))
 	{

security/selinux/hooks.c

@@ -69,6 +69,7 @@
 #include <linux/sysctl.h>
 #include <linux/audit.h>
 #include <linux/string.h>
+#include <linux/selinux.h>
 
 #include "avc.h"
 #include "objsec.h"
@@ -3420,7 +3421,13 @@ out:
 static int selinux_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata, u32 *seclen)
 {
 	int err = 0;
-	u32 peer_sid = selinux_socket_getpeer_dgram(skb);
+	u32 peer_sid;
+
+	if (skb->sk->sk_family == PF_UNIX)
+		selinux_get_inode_sid(SOCK_INODE(skb->sk->sk_socket),
+				      &peer_sid);
+	else
+		peer_sid = selinux_socket_getpeer_dgram(skb);
 
 	if (peer_sid == SECSID_NULL)
 		return -EINVAL;
@@ -3432,8 +3439,6 @@ static int selinux_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
 	return 0;
 }
 
-
-
 static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority)
 {
 	return sk_alloc_security(sk, family, priority);