sock: Introduce cred_to_ucred

To keep the coming code clear and to allow both the sock
code and the scm code to share the logic introduce a
fuction to translate from struct cred to struct ucred.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/socket.h

@@ -24,6 +24,9 @@ struct __kernel_sockaddr_storage {
 #include <linux/types.h>		/* pid_t			*/
 #include <linux/compiler.h>		/* __user			*/
 
+struct pid;
+struct cred;
+
 #define __sockaddr_check_size(size)	\
 	BUILD_BUG_ON(((size) > sizeof(struct __kernel_sockaddr_storage)))
 
@@ -309,6 +312,8 @@ struct ucred {
 #define IPX_TYPE	1
 
 #ifdef __KERNEL__
+extern void cred_to_ucred(struct pid *pid, const struct cred *cred, struct ucred *ucred);
+
 extern int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 extern int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
 			       int offset, int len);

net/core/sock.c

@@ -110,6 +110,7 @@
 #include <linux/tcp.h>
 #include <linux/init.h>
 #include <linux/highmem.h>
+#include <linux/user_namespace.h>
 
 #include <asm/uaccess.h>
 #include <asm/system.h>
@@ -749,6 +750,19 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 EXPORT_SYMBOL(sock_setsockopt);
 
 
+void cred_to_ucred(struct pid *pid, const struct cred *cred,
+		   struct ucred *ucred)
+{
+	ucred->pid = pid_vnr(pid);
+	ucred->uid = ucred->gid = -1;
+	if (cred) {
+		struct user_namespace *current_ns = current_user_ns();
+
+		ucred->uid = user_ns_map_uid(current_ns, cred, cred->euid);
+		ucred->gid = user_ns_map_gid(current_ns, cred, cred->egid);
+	}
+}
+
 int sock_getsockopt(struct socket *sock, int level, int optname,
 		    char __user *optval, int __user *optlen)
 {