linux-kernel - [PATCH 04/10] allow killing tasks in your own or child userns

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Date:	Thu, 24 Feb 2011 15:02:36 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Andrew Morton <akpm@...l.org>,
	containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Michael Kerrisk <mtk.manpages@...il.com>, dhowells@...hat.com,
	oleg@...l.hallyn.com, dlezcano@...l.hallyn.com,
	LSM <linux-security-module@...r.kernel.org>
Subject: [PATCH 04/10] allow killing tasks in your own or child userns


Changelog:
	Dec  8: Fixed bug in my check_kill_permission pointed out by
	        Eric Biederman.
	Dec 13: Apply Eric's suggestion to pass target task into kill_ok_by_cred()
	        for clarity
	Dec 31: address comment by Eric Biederman:
		don't need cred/tcred in check_kill_permission.
	Jan  1: use const cred struct.
	Jan 11: Per Bastian Blank's advice, clean up kill_ok_by_cred().
	Feb 16: kill_ok_by_cred: fix bad parentheses
	Feb 23: per akpm, let compiler inline kill_ok_by_cred

Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Acked-by: Daniel Lezcano <daniel.lezcano@...e.fr>
---
 kernel/signal.c |   30 ++++++++++++++++++++++--------
 1 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff1..12702b4 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -636,13 +636,33 @@ static inline bool si_fromuser(const struct siginfo *info)
 }
 
 /*
+ * called with RCU read lock from check_kill_permission()
+ */
+static int kill_ok_by_cred(struct task_struct *t)
+{
+	const struct cred *cred = current_cred();
+	const struct cred *tcred = __task_cred(t);
+
+	if (cred->user->user_ns == tcred->user->user_ns &&
+	    (cred->euid == tcred->suid ||
+	     cred->euid == tcred->uid ||
+	     cred->uid  == tcred->suid ||
+	     cred->uid  == tcred->uid))
+		return 1;
+
+	if (ns_capable(tcred->user->user_ns, CAP_KILL))
+		return 1;
+
+	return 0;
+}
+
+/*
  * Bad permissions for sending the signal
  * - the caller must hold the RCU read lock
  */
 static int check_kill_permission(int sig, struct siginfo *info,
 				 struct task_struct *t)
 {
-	const struct cred *cred, *tcred;
 	struct pid *sid;
 	int error;
 
@@ -656,14 +676,8 @@ static int check_kill_permission(int sig, struct siginfo *info,
 	if (error)
 		return error;
 
-	cred = current_cred();
-	tcred = __task_cred(t);
 	if (!same_thread_group(current, t) &&
-	    (cred->euid ^ tcred->suid) &&
-	    (cred->euid ^ tcred->uid) &&
-	    (cred->uid  ^ tcred->suid) &&
-	    (cred->uid  ^ tcred->uid) &&
-	    !capable(CAP_KILL)) {
+	    !kill_ok_by_cred(t)) {
 		switch (sig) {
 		case SIGCONT:
 			sid = task_session(t);
-- 
1.7.0.4

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