1 files changed, 34 insertions, 12 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff1..324eff5 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);
@@ -2421,9 +2435,13 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
 		return -EFAULT;
 
 	/* Not even root can pretend to send signals from the kernel.
-	   Nor can they impersonate a kill(), which adds source info.  */
-	if (info.si_code >= 0)
+	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
+	 */
+	if (info.si_code != SI_QUEUE) {
+		/* We used to allow any < 0 si_code */
+		WARN_ON_ONCE(info.si_code < 0);
 		return -EPERM;
+	}
 	info.si_signo = sig;
 
 	/* POSIX.1b doesn't mention process groups.  */
@@ -2437,9 +2455,13 @@ long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
 		return -EINVAL;
 
 	/* Not even root can pretend to send signals from the kernel.
-	   Nor can they impersonate a kill(), which adds source info.  */
-	if (info->si_code >= 0)
+	 * Nor can they impersonate a kill()/tgkill(), which adds source info.
+	 */
+	if (info->si_code != SI_QUEUE) {
+		/* We used to allow any < 0 si_code */
+		WARN_ON_ONCE(info->si_code < 0);
 		return -EPERM;
+	}
 	info->si_signo = sig;
 
 	return do_send_specific(tgid, pid, sig, info);