util-net: Itroduce send_fds/recv_fds routines

We will need these helpers to transfer file
descriptors from dumpee to our space.

Also make send_fd/recv_fd to be a wrappers over
send_fds/revc_fds to not duplicate the code.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util-net.h

@@ -28,6 +28,23 @@ struct scm_fdset {
 	int		msg;	/* We are to send at least one byte */
 };
 
-extern int send_fd(int sock, struct sockaddr_un *saddr, int len, int fd);
-extern int recv_fd(int sock);
+extern int send_fds(int sock, struct sockaddr_un *saddr, int saddr_len, int *fds, int nr_fds);
+extern int recv_fds(int sock, int *fds, int nr_fds);
+
+static inline int send_fd(int sock, struct sockaddr_un *saddr, int saddr_len, int fd)
+{
+	return send_fds(sock, saddr, saddr_len, &fd, 1);
+}
+
+static inline int recv_fd(int sock)
+{
+	int fd, ret;
+
+	ret = recv_fds(sock, &fd, 1);
+	if (ret)
+		return -1;
+
+	return fd;
+}
+
 #endif

util-net.c

@@ -4,6 +4,7 @@
 #include <errno.h>
 
 #include "compiler.h"
+#include "memcpy_64.h"
 #include "types.h"
 #include "syscall.h"
 
@@ -47,36 +48,64 @@ static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr, i
 	return (int *)CMSG_DATA(cmsg);
 }
 
-int send_fd(int sock, struct sockaddr_un *saddr, int len, int fd)
+int send_fds(int sock, struct sockaddr_un *saddr, int len, int *fds, int nr_fds)
 {
 	struct scm_fdset fdset;
 	int *cmsg_data;
+	int i, min_fd, ret;
 
 	cmsg_data = scm_fdset_init(&fdset, saddr, len);
-	scm_fdset_init_chunk(&fdset, 1);
-	*cmsg_data = fd;
+	for (i = 0; i < nr_fds; i += min_fd) {
+		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
+		scm_fdset_init_chunk(&fdset, min_fd);
+		builtin_memcpy(cmsg_data, &fds[i], sizeof(int) * min_fd);
 
-	return sys_sendmsg(sock, &fdset.hdr, 0);
+		ret = sys_sendmsg(sock, &fdset.hdr, 0);
+		if (ret <= 0)
+			return ret ? : -1;
+	}
+
+	return 0;
 }
 
-int recv_fd(int sock)
+int recv_fds(int sock, int *fds, int nr_fds)
 {
 	struct scm_fdset fdset;
 	struct cmsghdr *cmsg;
 	int *cmsg_data;
 	int ret;
+	int i, min_fd;
 
 	cmsg_data = scm_fdset_init(&fdset, NULL, 0);
-	scm_fdset_init_chunk(&fdset, 1);
-
-	ret = sys_recvmsg(sock, &fdset.hdr, 0);
-	if (ret < 0)
-		return ret;
-
-	cmsg = CMSG_FIRSTHDR(&fdset.hdr);
-	if (!cmsg || (cmsg->cmsg_type != SCM_RIGHTS))
-		return -2;
-
-	return *cmsg_data;
+	for (i = 0; i < nr_fds; i += min_fd) {
+		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
+		scm_fdset_init_chunk(&fdset, min_fd);
+
+		ret = sys_recvmsg(sock, &fdset.hdr, 0);
+		if (ret <= 0)
+			return ret ? : -1;
+
+		cmsg = CMSG_FIRSTHDR(&fdset.hdr);
+		if (!cmsg || cmsg->cmsg_type != SCM_RIGHTS)
+			return -EINVAL;
+
+		min_fd = (cmsg->cmsg_len - sizeof(struct cmsghdr)) / sizeof(int);
+		/*
+		 * In case if kernel screwed the recepient, most probably
+		 * the caller stack frame will be overwriten, just scream
+		 * and exit.
+		 *
+		 * FIXME Need to sanitize util.h to be able to include it
+		 * into files which do not have glibc and a couple of
+		 * sys_write_ helpers. Meawhile opencoded BUG_ON here.
+		 */
+		if (unlikely(min_fd > CR_SCM_MAX_FD))
+			*(volatile unsigned long *)NULL = 0xdead0000 + __LINE__;
+		if (unlikely(min_fd <= 0))
+			return -1;
+		builtin_memcpy(&fds[i], cmsg_data, sizeof(int) * min_fd);
+	}
+
+	return 0;
 }