[Devel] Re: [PATCH 1/2] signals: kill(-1) should only signal processes in the same namespace

[Daniel Hokka Zakrisson]

sukadev at us.ibm.com wrote:
> Daniel Hokka Zakrisson [daniel at hozac.com] wrote:
> | While moving Linux-VServer to using pid namespaces, I noticed that
> | kill(-1) from inside a pid namespace is currently signalling every
> | process in the entire system, including processes that are otherwise
> | unreachable from the current process.
> |
> | This patch fixes it by making sure that only processes which are in
> | the same pid namespace as current get signalled.
> |
> | Signed-off-by: Daniel Hokka Zakrisson <daniel at hozac.com>
> |
> | diff --git a/include/linux/pid_namespace.h
> b/include/linux/pid_namespace.h
> | index caff528..4cf41bd 100644
> | --- a/include/linux/pid_namespace.h
> | +++ b/include/linux/pid_namespace.h
> | @@ -40,6 +40,8 @@ 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 task_in_pid_ns(struct task_struct *tsk,
> | +			  struct pid_namespace *pid_ns);
> |
> |   static inline void put_pid_ns(struct pid_namespace *ns)
> |   {
> | @@ -72,6 +74,12 @@ static inline void zap_pid_ns_processes(struct
> | pid_namespace *ns)
> |   {
> |   	BUG();
> |   }
> | +
> | +static inline int task_in_pid_ns(struct task_struct *tsk,
> | +				  struct pid_namespace *ns)
> | +{
> | +	return 1;
> | +}
> |   #endif /* CONFIG_PID_NS */
> |
> |   static inline struct pid_namespace *task_active_pid_ns(struct
> | task_struct *tsk)
> | diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> | index 98702b4..3e71011 100644
> | --- a/kernel/pid_namespace.c
> | +++ b/kernel/pid_namespace.c
> | @@ -188,6 +188,26 @@ void zap_pid_ns_processes(struct pid_namespace
> *pid_ns)
> |   	return;
> |   }
> |
> | +/*
> | + * Checks whether tsk has a pid in the pid namespace ns.
> | + * Must be called with tasklist_lock read-locked or under
> rcu_read_lock()
> | + */
> | +int task_in_pid_ns(struct task_struct *tsk, struct pid_namespace *ns)
> | +{
> | +	struct pid *pid = task_pid(tsk);
> | +
> | +	if (!pid)
> | +		return 0;
> | +
> | +	if (pid->level < ns->level)
> | +		return 0;
>
> ns can be NULL if tsk is exiting.

ns is from current, and this is currently only called from
kill_something_info, so it should not be exiting in this path.

> Like Pavel said, we had couple of attempts to fix the larger problem of
> signal semantics in containers but did not have a consensus on handling
> blocked/unhandled signals to container-init.
>
> It would still be good to fix this "kill -1" problem.

It is a separate issue, so, yeah.

> Eric had a slightly optimized interface, 'pid_in_pid_ns()' in following
> patchset. Maybe we could use that ?
>
> https://lists.linux-foundation.org/pipermail/containers/2007-December/009174.html

See my response to Eric. I think that patch looks good... (Well, nr could
be set to 2 initially, to avoid the nr <= 1 check.)

> | +
> | +	if (pid->numbers[ns->level].ns != ns)
> | +		return 0;
> | +
> | +	return 1;
> | +}
> | +
> |   static __init int pid_namespaces_init(void)
> |   {
> |   	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
> | diff --git a/kernel/signal.c b/kernel/signal.c
> | index 6c0958e..93713a5 100644
> | --- a/kernel/signal.c
> | +++ b/kernel/signal.c
> | @@ -1145,7 +1145,8 @@ static int kill_something_info(int sig, struct
> | siginfo *info, int pid)
> |   		struct task_struct * p;
> |
> |   		for_each_process(p) {
> | -			if (p->pid > 1 && !same_thread_group(p, current)) {
> | +			if (p->pid > 1 && !same_thread_group(p, current) &&
> | +			    task_in_pid_ns(p, current->nsproxy->pid_ns)) {
> |   				int err = group_send_sig_info(sig, info, p);
> |   				++count;
> |   				if (err != -EPERM)
> | --
> | 1.5.5.1

-- 
Daniel Hokka Zakrisson
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