[Devel] [PATCH RH7 25/32] ns: allow ns_entries to have custom symlink content

[Pavel Tikhomirov]

From: Kirill Tkhai <ktkhai at virtuozzo.com>

Patch series "Expose task pid_ns_for_children to userspace".

pid_ns_for_children set by a task is known only to the task itself, and
it's impossible to identify it from outside.

It's a big problem for checkpoint/restore software like CRIU, because it
can't correctly handle tasks, that do setns(CLONE_NEWPID) in proccess of
their work.  If they have a custom pid_ns_for_children before dump, they
must have the same ns after restore.  Otherwise, restored task bumped
into enviroment it does not expect.

This patchset solves the problem.  It exposes pid_ns_for_children to ns
directory in standard way with the name "pid_for_children":

  ~# ls /proc/5531/ns -l | grep pid
  lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid -> pid:[4026531836]
  lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid_for_children -> pid:[4026532286]

This patch (of 2):

Make possible to have link content prefix yyy different from the link
name xxx:

  $ readlink /proc/[pid]/ns/xxx
  yyy:[4026531838]

This will be used in next patch.

Link: http://lkml.kernel.org/r/149201120318.6007.7362655181033883000.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Reviewed-by: Cyrill Gorcunov <gorcunov at openvz.org>
Acked-by: Andrei Vagin <avagin at virtuozzo.com>
Cc: Andreas Gruenbacher <agruenba at redhat.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Michael Kerrisk <mtk.manpages at googlemail.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: Oleg Nesterov <oleg at redhat.com>
Cc: Paul Moore <paul at paul-moore.com>
Cc: Eric Biederman <ebiederm at xmission.com>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Serge Hallyn <serge at hallyn.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>

(cherry picked from VZ8 commit 25b14e92af1a563c7331466ca59188f88050bbf0)

https://jira.sw.ru/browse/PSBM-102357

Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 fs/nsfs.c               | 4 +++-
 include/linux/proc_ns.h | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/nsfs.c b/fs/nsfs.c
index fb5215552a8d..ade35cf01d0a 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -190,9 +190,11 @@ int ns_get_name(char *buf, size_t size, struct task_struct *task,
 {
 	struct ns_common *ns;
 	int res = -ENOENT;
+	const char *name;
 	ns = ns_ops->get(task);
 	if (ns) {
-		res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
+		name = ns_ops->real_ns_name ? : ns_ops->name;
+		res = snprintf(buf, size, "%s:[%u]", name, ns->inum);
 		ns_ops->put(ns);
 	}
 	return res;
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index a8645c5eb679..ea002b8e5ab9 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -14,6 +14,7 @@ struct path;
 
 struct proc_ns_operations {
 	const char *name;
+	const char *real_ns_name;
 	int type;
 	struct ns_common *(*get)(struct task_struct *task);
 	void (*put)(struct ns_common *ns);
-- 
2.24.1