[PATCH 4/7][v6] Define siginfo_from_ancestor_ns()

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Wed, 24 Dec 2008 13:46:02 -0800
Subject: [PATCH 4/7][v6] Define siginfo_from_ancestor_ns()

Determine if sender of a signal is from an ancestor namespace. This
function will be used in a follow-on patch.

This is based on discussions on the patch from Oleg Nesterov and me
http://lkml.org/lkml/2008/11/25/462.

Changelog[v6]:
	- (Oleg Nesterov) Simplify/correct comments
	- (Oleg Nesterov) Remove 'ns == NULL' check since task_active_pid_ns()
	   will return a valid ns for the target.
	- (Roland Mcgrath) Remove incorrect SI_ASYNCIO check in
	   siginfo_from_user().
Changelog[v5]:
	- (Oleg Nesterov) Put siginfo_from_ancestor_ns() back under
	  CONFIG_PID_NS.
	- (Oleg Nesterov) Remove the warning in rt_sigqueueinfo().

Changelog[v4]:
	- siginfo_from_ancestor_ns() is fairly clean and it does not need
	  to be under CONFIG_PID_NS. Only siginfo_from_user() needs to be.
	- Warn if rt_sigqueueinfo() uses SI_ASYNCIO.
	- Added a check for pid-ns of receiver being NULL (in case it is
	  exiting).

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
 kernel/signal.c |   37 +++++++++++++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index bb3b6f5..d0dfa0d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -820,6 +820,43 @@ static inline int legacy_queue(struct sigpending *signals, int sig)
 {
 	return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
 }
+/*
+ * Return 1 if this signal originated directly from a user process (i.e via
+ * kill(), tkill(), sigqueue()).  Return 0 otherwise.
+ */
+#ifdef CONFIG_PID_NS
+static inline int siginfo_from_user(siginfo_t *info)
+{
+	if (!is_si_special(info) && SI_FROMUSER(info))
+		return 1;
+
+	return 0;
+}
+
+static inline int siginfo_from_ancestor_ns(struct task_struct *t,
+			siginfo_t *info)
+{
+	/*
+	 * If we do not have a pid in the receiver's namespace,
+	 * we must be from an ancestor namespace.
+	 */
+	if (siginfo_from_user(info) &&
+			task_pid_nr_ns(current, task_active_pid_ns(t)) <= 0) {
+		return 1;
+	}
+
+	return 0;
+}
+
+#else
+
+static inline int siginfo_from_ancestor_ns(struct task_struct *t,
+			siginfo_t *info)
+{
+	return 0;
+}
+
+#endif
 
 static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
 			int group, int from_ancestor_ns)
-- 
1.5.2.5