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-   -   UBUNTU: SAUCE: Add reboot_pid_ns to handle the reboot syscall (http://www.linux-archive.org/ubuntu-kernel-team/624902-ubuntu-sauce-add-reboot_pid_ns-handle-reboot-syscall.html)

Daniel Lezcano 01-05-2012 08:06 AM

UBUNTU: SAUCE: Add reboot_pid_ns to handle the reboot syscall
 
In the case of a child pid namespace, rebooting the system does not
really makes sense. When the pid namespace is used in conjunction
with the other namespaces in order to create a linux container, the
reboot syscall leads to some problems.

A container can reboot the host. That can be fixed by dropping
the sys_reboot capability but we are unable to correctly to poweroff/
halt/reboot a container and the container stays stuck at the shutdown
time with the container's init process waiting indefinitively.

After several attempts, no solution from userspace was found to reliabily
handle the shutdown from a container.

This patch propose to make the init process of the child pid namespace to
exit with a signal status set to : SIGINT if the child pid namespace called
"halt/poweroff" and SIGHUP if the child pid namespace called "reboot".
When the reboot syscall is called and we are not in the initial
pid namespace, we kill the pid namespace for "HALT", "POWEROFF", "RESTART",
and "RESTART2". Otherwise we return EINVAL.

Returning EINVAL is also an easy way to check if this feature is supported
by the kernel when invoking another 'reboot' option like CAD.

By this way the parent process of the child pid namespace knows if
it rebooted or not and can take the right decision.

Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>

BugLink: http://bugs.launchpad.net/bugs/914676

(backported from https://lkml.org/lkml/2012/1/5/58)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
include/linux/pid_namespace.h | 8 +++++++-
kernel/pid_namespace.c | 33 +++++++++++++++++++++++++++++++++
kernel/sys.c | 8 ++++++++
3 files changed, 48 insertions(+), 1 deletions(-)

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 38d1032..5f761d6 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -30,6 +30,7 @@ struct pid_namespace {
#ifdef CONFIG_BSD_PROCESS_ACCT
struct bsd_acct_struct *bacct;
#endif
+ int reboot;
};

extern struct pid_namespace init_pid_ns;
@@ -45,6 +46,7 @@ static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
extern struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *ns);
extern void free_pid_ns(struct kref *kref);
extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
+extern int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd);

static inline void put_pid_ns(struct pid_namespace *ns)
{
@@ -72,11 +74,15 @@ static inline void put_pid_ns(struct pid_namespace *ns)
{
}

-
static inline void zap_pid_ns_processes(struct pid_namespace *ns)
{
BUG();
}
+
+static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
+{
+ return 0;
+}
#endif /* CONFIG_PID_NS */

extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk);
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index e9c9adc..ac84fd3 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -15,6 +15,7 @@
#include <linux/acct.h>
#include <linux/slab.h>
#include <linux/proc_fs.h>
+#include <linux/reboot.h>

#define BITS_PER_PAGE (PAGE_SIZE*8)

@@ -187,10 +188,42 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
rc = sys_wait4(-1, NULL, __WALL, NULL);
} while (rc != -ECHILD);

+ if (pid_ns->reboot)
+ current->signal->group_exit_code = pid_ns->reboot;
+
acct_exit_ns(pid_ns);
return;
}

+int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
+{
+ if (pid_ns == &init_pid_ns)
+ return 0;
+
+ switch(cmd) {
+ case LINUX_REBOOT_CMD_RESTART2:
+ case LINUX_REBOOT_CMD_RESTART:
+ pid_ns->reboot = SIGHUP;
+ break;
+
+ case LINUX_REBOOT_CMD_POWER_OFF:
+ case LINUX_REBOOT_CMD_HALT:
+ pid_ns->reboot = SIGINT;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ read_lock(&tasklist_lock);
+ force_sig(SIGKILL, pid_ns->child_reaper);
+ read_unlock(&tasklist_lock);
+
+ do_exit(0);
+
+ /* Not reached */
+ return 0;
+}
+
static __init int pid_namespaces_init(void)
{
pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
diff --git a/kernel/sys.c b/kernel/sys.c
index e7aa654..3d2b2d0 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -444,6 +444,14 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
magic2 != LINUX_REBOOT_MAGIC2C))
return -EINVAL;

+ /* In case the pid namespaces are enabled, the current task is in a
+ * child pid_namespace and the command is handled by 'reboot_pid_ns',
+ * this one will invoke 'do_exit'.
+ */
+ ret = reboot_pid_ns(task_active_pid_ns(current), cmd);
+ if (ret)
+ return ret;
+
/* Instead of trying to make the power_off code look like
* halt when pm_power_off is not set do it the easy way.
*/
--
1.7.5.4


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