kerndat: check the SIOCUNIXFILE ioctl for unix sockets

This ioctl opens a file to which a socket is bound and
returns a file descriptor. This file descriptor can be used to get
mnt_id and a file path.
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-check.c

@@ -1073,6 +1073,14 @@ static int check_sk_netns(void)
 	return 0;
 }
 
+static int check_sk_unix_file(void)
+{
+	if (!kdat.sk_unix_file)
+		return -1;
+
+	return 0;
+}
+
 static int (*chk_feature)(void);
 
 /*
@@ -1267,6 +1275,7 @@ static struct feature_list feature_list[] = {
 	{ "uffd-noncoop", check_uffd_noncoop },
 	{ "can_map_vdso", check_can_map_vdso},
 	{ "sk_ns", check_sk_netns },
+	{ "sk_unix_file", check_sk_unix_file },
 	{ "nsid", check_nsid },
 	{ "link_nsid", check_link_nsid},
 	{ NULL, NULL },

criu/include/kerndat.h

@@ -48,6 +48,7 @@ struct kerndat_s {
 	enum loginuid_func luid;
 	bool compat_cr;
 	bool sk_ns;
+	bool sk_unix_file;
 	bool tun_ns;
 	enum pagemap_func pmap;
 	unsigned int has_xtlocks;

criu/include/sockets.h

@@ -93,5 +93,6 @@ extern int set_netns(uint32_t ns_id);
 #endif
 
 extern int kerndat_socket_netns(void);
+extern int kerndat_socket_unix_file(void);
 
 #endif /* __CR_SOCKETS_H__ */

criu/kerndat.c

@@ -1003,6 +1003,8 @@ int kerndat_init(void)
 		ret = kerndat_socket_netns();
 	if (!ret)
 		ret = kerndat_tun_netns();
+	if (!ret)
+		ret = kerndat_socket_unix_file();
 	if (!ret)
 		ret = kerndat_nsid();
 	if (!ret)

criu/sk-unix.c

 #include <sys/socket.h>
+#include <sys/ioctl.h>
 #include <linux/netlink.h>
 #include <linux/rtnetlink.h>
 #include <libnl3/netlink/msg.h>
@@ -29,6 +30,7 @@
 #include "external.h"
 #include "crtools.h"
 #include "fdstore.h"
+#include "kerndat.h"
 
 #include "protobuf.h"
 #include "images/sk-unix.pb-c.h"
@@ -196,6 +198,34 @@ static int write_unix_entry(struct unix_sk_desc *sk)
 	return ret;
 }
 
+#ifndef SIOCUNIXFILE
+#define SIOCUNIXFILE (SIOCPROTOPRIVATE + 0) /* open a socket file with O_PATH */
+#endif
+
+int kerndat_socket_unix_file(void)
+{
+	int sk, fd;
+
+	sk = socket(AF_UNIX, SOCK_DGRAM, 0);
+	if (sk < 0) {
+		pr_perror("Unable to create socket");
+		return -1;
+	}
+	fd = ioctl(sk, SIOCUNIXFILE);
+	if (fd < 0 && errno != ENOENT) {
+		pr_warn("Unable to open a socket file: %m\n");
+		kdat.sk_unix_file = false;
+		close(sk);
+		return 0;
+	}
+	close(sk);
+	close(fd);
+
+	kdat.sk_unix_file = true;
+
+	return 0;
+}
+
 static int resolve_rel_name(struct unix_sk_desc *sk, const struct fd_parms *p)
 {
 	rel_name_desc_t *rel_name = sk->rel_name;