ns: Fix wrong opened net ns file

Since net ns is assigned after prepare_fds() and,
in common case, at the moment of open_ns_fd() call
task points to a net ns, which differs to its target
net ns, we can't get the ns from a task. So, get it
from fdstore. Also, support userns ns fds.

v2: Add comment
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/namespaces.c

@@ -25,6 +25,7 @@
 #include "namespaces.h"
 #include "net.h"
 #include "cgroup.h"
+#include "fdstore.h"
 
 #include "protobuf.h"
 #include "util.h"
@@ -515,8 +516,21 @@ static int open_ns_fd(struct file_desc *d, int *new_fd)
 	struct ns_file_info *nfi = container_of(d, struct ns_file_info, d);
 	struct pstree_item *item, *t;
 	struct ns_desc *nd = NULL;
+	struct ns_id *ns;
+	int nsfd_id, fd;
 	char path[64];
-	int fd;
+
+	for (ns = ns_ids; ns != NULL; ns = ns->next) {
+		if (ns->id != nfi->nfe->ns_id)
+			continue;
+		/* Check for CLONE_XXX as we use fdstore only if flag is set */
+		if (ns->nd == &net_ns_desc && (root_ns_mask & CLONE_NEWNET))
+			nsfd_id = ns->net.nsfd_id;
+		else
+			break;
+		fd = fdstore_get(nsfd_id);
+		goto check_open;
+	}
 
 	/*
 	 * Find out who can open us.
@@ -534,6 +548,10 @@ static int open_ns_fd(struct file_desc *d, int *new_fd)
 			item = t;
 			nd = &net_ns_desc;
 			break;
+		} else if (ids->user_ns_id == nfi->nfe->ns_id) {
+			item = t;
+			nd = &user_ns_desc;
+			break;
 		} else if (ids->ipc_ns_id == nfi->nfe->ns_id) {
 			item = t;
 			nd = &ipc_ns_desc;
@@ -567,6 +585,7 @@ static int open_ns_fd(struct file_desc *d, int *new_fd)
 	path[sizeof(path) - 1] = '\0';
 
 	fd = open(path, nfi->nfe->flags);
+check_open:
 	if (fd < 0) {
 		pr_perror("Can't open file %s on restore", path);
 		return fd;