[PATCH 11/23] tracehook: tracehook_consider_ignored_signal

Roland McGrath
2008-07-17T07:31:57Z

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>
---
include/linux/tracehook.h | 19 +++++++++++++++++++
kernel/signal.c | 27 ++++++++++++++++-----------
2 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 2d1426f..8cffd34 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 02d3a11..f68fb01 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);
}

/*
@@ -2324,7 +2329,7 @@ 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);