[CRIU] [PATCH v2 3/3] criu: unset loginuid value before creating userns

[Dmitry Safonov]

The value of loginuid cannot be changed inside container, with the
exception if it was not set yet. This value is inherited on fork() from
parent.

So, to restore original loginuid values for all tasks:
  - unset the container parent loginuid
  - all children will have this value unsetted
  - on child restore set value from dump

See http://lxr.free-electrons.com/source/kernel/audit.c#L635
https://jira.sw.ru/browse/PSBM-41993

Signed-off-by: Dmitry Safonov <dsafonov at odin.com>
---
 cr-restore.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/cr-restore.c b/cr-restore.c
index 00fcd57..699e307 100644
--- a/cr-restore.c
+++ b/cr-restore.c
@@ -1811,6 +1811,28 @@ static void ignore_kids(void)
 		pr_perror("Restoring CHLD sigaction failed");
 }
 
+static unsigned int saved_loginuid = 0;
+
+static void prepare_userns_hook(void)
+{
+	pid_t pid = getpid();
+
+	/*
+	 * Save old loginuid and set it to 4294967295:
+	 * this value means that loginuid is unset and it will be inherited.
+	 * After you set some value to /proc/<>/loginuid it can't be changed
+	 * inside container due to permissions.
+	 * But you still can set this value if it was unset (4294967295/-1).
+	 */
+	saved_loginuid = parse_pid_loginuid(pid);
+	prepare_pid_loginuid(pid, 4294967295);
+}
+
+static void restore_origin_ns_hook(void)
+{
+	prepare_pid_loginuid(getpid(), saved_loginuid);
+}
+
 static int restore_root_task(struct pstree_item *init)
 {
 	enum trace_flags flag = TRACE_ALL;
@@ -1854,6 +1876,8 @@ static int restore_root_task(struct pstree_item *init)
 		return -1;
 	}
 
+	prepare_userns_hook();
+
 	if (prepare_namespace_before_tasks())
 		return -1;
 
@@ -1864,6 +1888,8 @@ static int restore_root_task(struct pstree_item *init)
 	if (ret < 0)
 		goto out;
 
+	restore_origin_ns_hook();
+
 	if (root_as_sibling) {
 		struct sigaction act;
 		/*
-- 
2.6.3