[Devel] [PATCH 1/2] ns: allow ns_entries to have custom symlink content

[Kirill Tkhai]

ms commit: 25b14e92af1a563c7331466ca59188f88050bbf0

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>

https://jira.sw.ru/browse/PSBM-58669

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 fs/proc/namespaces.c    |    4 +++-
 include/linux/proc_ns.h |    1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 54bdc6701e9..e70c2d3f66a 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -150,6 +150,7 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
 	struct proc_inode *ei = PROC_I(inode);
 	const struct proc_ns_operations *ns_ops = ei->ns.ns_ops;
 	struct task_struct *task;
+	const char *link_name;
 	void *ns;
 	char name[50];
 	int len = -EACCES;
@@ -166,7 +167,8 @@ static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int bufl
 	if (!ns)
 		goto out_put_task;
 
-	snprintf(name, sizeof(name), "%s:[%u]", ns_ops->name, ns_ops->inum(ns));
+	link_name = ns_ops->real_ns_name ? : ns_ops->name;
+	snprintf(name, sizeof(name), "%s:[%u]", link_name, ns_ops->inum(ns));
 	len = strlen(name);
 
 	if (len > buflen)
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index 5478e144c50..b8dc2bca257 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -10,6 +10,7 @@ struct nsproxy;
 
 struct proc_ns_operations {
 	const char *name;
+	const char *real_ns_name;
 	int type;
 	void *(*get)(struct task_struct *task);
 	void (*put)(void *ns);