tracehook: tracehook_consider_ignored_signal

This defines tracehook_consider_ignored_signal() has a fine-grained hook
for deciding to prevent the normal short-circuit of sending an ignored
signal, as ptrace does.  There is no change, only cleanup.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 35 insertions, 11 deletions

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 2d1426f8e33b..8cffd34f88d5 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -312,4 +312,23 @@ static inline void tracehook_signal_handler(int sig, siginfo_t *info,
                 ptrace_notify(SIGTRAP);
 }
 
+/**
+ * tracehook_consider_ignored_signal - suppress short-circuit of ignored signal
+ * @task:               task receiving the signal
+ * @sig:                signal number being sent
+ * @handler:            %SIG_IGN or %SIG_DFL
+ *
+ * Return zero iff tracing doesn't care to examine this ignored signal,
+ * so it can short-circuit normal delivery and never even get queued.
+ * Either @handler is %SIG_DFL and @sig's default is ignore, or it's %SIG_IGN.
+ *
+ * Called with @task->sighand->siglock held.
+ */
+static inline int tracehook_consider_ignored_signal(struct task_struct *task,
+                                                    int sig,
+                                                    void __user *handler)
+{
+        return (task_ptrace(task) & PT_PTRACED) != 0;
+}
+
 #endif  /* <linux/tracehook.h> */
diff --git a/kernel/signal.c b/kernel/signal.c
index 8715c18b27b9..9efd1cee6d0b 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -22,6 +22,7 @@
 #include <linux/ptrace.h>
 #include <linux/signal.h>
 #include <linux/signalfd.h>
+#include <linux/tracehook.h>
 #include <linux/capability.h>
 #include <linux/freezer.h>
 #include <linux/pid_namespace.h>
@@ -39,24 +40,21 @@
 
 static struct kmem_cache *sigqueue_cachep;
 
-static int __sig_ignored(struct task_struct *t, int sig)
+static void __user *sig_handler(struct task_struct *t, int sig)
 {
-        void __user *handler;
+        return t->sighand->action[sig - 1].sa.sa_handler;
+}
 
+static int sig_handler_ignored(void __user *handler, int sig)
+{
         /* Is it explicitly or implicitly ignored? */
-
-        handler = t->sighand->action[sig - 1].sa.sa_handler;
         return handler == SIG_IGN ||
                 (handler == SIG_DFL && sig_kernel_ignore(sig));
 }
 
 static int sig_ignored(struct task_struct *t, int sig)
 {
-        /*
-         * Tracers always want to know about signals..
-         */
-        if (t->ptrace & PT_PTRACED)
-                return 0;
+        void __user *handler;
 
         /*
          * Blocked signals are never ignored, since the
@@ -66,7 +64,14 @@ static int sig_ignored(struct task_struct *t, int sig)
         if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
                 return 0;
 
-        return __sig_ignored(t, sig);
+        handler = sig_handler(t, sig);
+        if (!sig_handler_ignored(handler, sig))
+                return 0;
+
+        /*
+         * Tracers may want to know about even ignored signals.
+         */
+        return !tracehook_consider_ignored_signal(t, sig, handler);
 }
 
 /*
@@ -2298,7 +2303,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
                  *   (for example, SIGCHLD), shall cause the pending signal to
                  *   be discarded, whether or not it is blocked"
                  */
-                if (__sig_ignored(t, sig)) {
+                if (sig_handler_ignored(sig_handler(t, sig), sig)) {
                         sigemptyset(&mask);
                         sigaddset(&mask, sig);
                         rm_from_queue_full(&mask, &t->signal->shared_pending);