[Devel] Re: [PATCH 3/9] pid: Implement ns_of_pid.

[sukadev at us.ibm.com]

Eric W. Biederman [ebiederm at xmission.com] wrote:
| sukadev at us.ibm.com writes:
| 
| >
| > My patch refers to this function as pid_active_pid_ns() - I have
| > been meaning to send that out on top of your signals patch.
| > Since a pid has many namespaces, we have been using 'active pid ns'
| > to refer to this ns.
| 
| Currently we don't ask for any of the others, and the namespace
| the pid came from is special.  That fundamentally is the namespace
| of the pid.  The rest byproducts of being in that pid namespace,
| as we could derive them by walking the namespace's parent list.
| 
| > Even your next patch modifies task_active_pid_ns() to use this.
| > So can we rename this functio to pid_active_pid_ns() ?
| 
| I'd be more inclined to rename task_active_pid_ns to task_pid_ns.
| 
| And to rename pid_in_pid_ns that Pavel has issues with to pid_in_ns.
| 
| When I read active_pid_ns I wonder what the other namespaces are
| that we are distinguishing this from.  They do exist in the
| implementation but so far it is a complete don't care.

Well, there are interfaces like pid_nr_ns() and pid_in_ns() and
task_in_pid_ns() that imply existence of other namespaces and
for that reason we added 'active' in the name. 

But I am fine with the terse name and of course we should remove
the the 'active' in task_active_pid_ns() also.

| 
| So I expect being as terse as we can while still conveying all of the
| relevant information is the most maintainable long term.
| 
| Eric

I did some initial testing on your patchset (minus patch 5) and noticed
that it seems to be missing the patch to address kill -1 semantics
(here is the earlier version). 

---

This patch implements task_in_pid_ns and uses it to limit cap_set_all
and sys_kill(-1,) to only those tasks in the current pid namespace.

Without this we have a setup for a very nasty surprise.

Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
---
 include/linux/pid_namespace.h |    2 ++
 kernel/capability.c           |    3 +++
 kernel/pid.c                  |   11 +++++++++++
 kernel/signal.c               |    5 ++++-
 4 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 0227e68..b454678 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -78,4 +78,6 @@ static inline struct task_struct *task_child_reaper(struct task_struct *tsk)
 	return tsk->nsproxy->pid_ns->child_reaper;
 }

+extern int task_in_pid_ns(struct task_struct *tsk, struct pid_namespace *ns);
+
 #endif /* _LINUX_PID_NS_H */
diff --git a/kernel/capability.c b/kernel/capability.c
index efbd9cd..a801016 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -125,6 +125,7 @@ static inline int cap_set_all(kernel_cap_t *effective,
 			       kernel_cap_t *inheritable,
 			       kernel_cap_t *permitted)
 {
+     struct pid_namespace *pid_ns = current->nsproxy->pid_ns;
      struct task_struct *g, *target;
      int ret = -EPERM;
      int found = 0;
@@ -132,6 +133,8 @@ static inline int cap_set_all(kernel_cap_t *effective,
      do_each_thread(g, target) {
              if (target == current || is_container_init(target->group_leader))
                      continue;
+             if (!task_in_pid_ns(target, pid_ns))
+		     continue;
              found = 1;
 	     if (security_capset_check(target, effective, inheritable,
 						permitted))
diff --git a/kernel/pid.c b/kernel/pid.c
index f815455..1c332ca 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -430,6 +430,17 @@ struct pid *find_get_pid(pid_t nr)
 	return pid;
 }

+static int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)
+{
+	return pid && (ns->level <= pid->level) &&
+		pid->numbers[ns->level].ns == ns;
+}
+
+int task_in_pid_ns(struct task_struct *task, struct pid_namespace *ns)
+{
+	return pid_in_pid_ns(task_pid(task), ns);
+}
+
 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 {
 	struct upid *upid;
diff --git a/kernel/signal.c b/kernel/signal.c
index 1200630..8f5a31f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1147,10 +1147,13 @@ static int kill_something_info(int sig, struct siginfo *info, int pid)
 	} else if (pid == -1) {
 		int retval = 0, count = 0;
 		struct task_struct * p;
+		struct pid_namespace *ns = current->nsproxy->pid_ns;

 		read_lock(&tasklist_lock);
 		for_each_process(p) {
-			if (p->pid > 1 && !same_thread_group(p, current)) {
+			if (!is_container_init(p) &&
+			    !same_thread_group(p, current) &&
+			    task_in_pid_ns(p, ns)) {
 				int err = group_send_sig_info(sig, info, p);
 				++count;
 				if (err != -EPERM)
-- 
1.5.3.rc6.17.g1911
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