kerndat: Check that "/proc/[pid]/status" file has NS{pid, ..} lines

If there is nested pid_ns, we need to be able to get pid in
the whole pid hierarhy. This may be taken from "/proc/[pid]/status"
file only. Check, that kernel has support for it.

v3: Add criu feature check

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-check.c

@@ -1073,6 +1073,17 @@ static int check_sk_netns(void)
 	return 0;
 }
 
+static int check_ns_pid(void)
+{
+	if (kerndat_has_nspid() < 0)
+		return -1;
+
+	if (!kdat.has_nspid)
+		return -1;
+
+	return 0;
+}
+
 static int (*chk_feature)(void);
 
 /*
@@ -1180,6 +1191,7 @@ int cr_check(void)
 		ret |= check_uffd();
 		ret |= check_uffd_noncoop();
 		ret |= check_sk_netns();
+		ret |= check_ns_pid();
 	}
 
 	/*
@@ -1261,6 +1273,7 @@ static struct feature_list feature_list[] = {
 	{ "sk_ns", check_sk_netns },
 	{ "nsid", check_nsid },
 	{ "link_nsid", check_link_nsid},
+	{ "ns_pid", check_ns_pid},
 	{ NULL, NULL },
 };
 

criu/include/kerndat.h

@@ -66,6 +66,7 @@ struct kerndat_s {
 #endif
 	bool has_nsid;
 	bool has_link_nsid;
+	bool has_nspid;
 };
 
 extern struct kerndat_s kdat;
@@ -88,5 +89,6 @@ extern int kerndat_fs_virtualized(unsigned int which, u32 kdev);
 
 extern int kerndat_tcp_repair();
 extern int kerndat_uffd(void);
+extern int kerndat_has_nspid(void);
 
 #endif /* __CR_KERNDAT_H__ */

criu/kerndat.c

@@ -848,6 +848,32 @@ out_unmap:
 	return ret;
 }
 
+int kerndat_has_nspid(void)
+{
+	struct bfd f;
+	int ret = -1;
+	char *str;
+
+	f.fd = open("/proc/self/status", O_RDONLY);
+	if (f.fd < 0) {
+		pr_perror("Can't open /proc/self/status");
+		return -1;
+	}
+	if (bfdopenr(&f))
+		return -1;
+	while ((str = breadline(&f)) != NULL) {
+		if (IS_ERR(str))
+			goto close;
+		if (!strncmp(str, "NSpid:", 6)) {
+			kdat.has_nspid = true;
+			break;
+		}
+	}
+	ret = 0;
+close:
+	bclose(&f);
+	return ret;
+}
 int kerndat_init(void)
 {
 	int ret;
@@ -904,6 +930,8 @@ int kerndat_init(void)
 		ret = kerndat_socket_netns();
 	if (!ret)
 		ret = kerndat_nsid();
+	if (!ret)
+		ret = kerndat_has_nspid();
 
 	kerndat_lsm();
 	kerndat_mmap_min_addr();

criu/namespaces.c

@@ -26,6 +26,7 @@
 #include "namespaces.h"
 #include "net.h"
 #include "cgroup.h"
+#include "kerndat.h"
 
 #include "protobuf.h"
 #include "util.h"
@@ -803,6 +804,10 @@ static int set_ns_hookups(struct ns_id *ns)
 			pr_err("Wrong determined NS_ROOT, or root_item has NS_OTHER user_ns\n");
 			goto out;
 		}
+		if (nd == &pid_ns_desc && !kdat.has_nspid) {
+			pr_err("Can't dump nested pid ns\n");
+			goto out;
+		}
 		list_add(&ns->siblings, &ns->parent->children);
 	}