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Subject[PATCH 15/16] ptrace: make sure SIGNAL_NOTIFY_CONT is checked after ptrace_signal()
Date
ptrace_signal() releases siglock and signal delivery may continue
afterwards. SIGNAL_NOTIFY_CONT can be set inbetween and should be
checked after returning from the function.

* Restart from the top if ptrace_signal() returns 0.

* Factor out CLD_CONTINUED check code into notify_parent_cont() and
check before returning from get_signal_to_deliver() too.

With the latter, the former isn't strictly necessary but it's still
better to do it to document what's going on if for nothing else.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
---
kernel/signal.c | 38 +++++++++++++++++++++++++++-----------
1 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 7b6f972..5eddda6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2019,6 +2019,19 @@ static int ptrace_signal(int signr, siginfo_t *info,
return signr;
}

+static inline void notify_parent_cont(void)
+{
+ /*
+ * Every stopped thread should go through this function after
+ * waking up. Check to see if we should notify the parent.
+ */
+ if (unlikely(current->signal->flags & SIGNAL_NOTIFY_CONT)) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current->group_leader, CLD_CONTINUED);
+ read_unlock(&tasklist_lock);
+ }
+}
+
int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
struct pt_regs *regs, void *cookie)
{
@@ -2035,15 +2048,7 @@ relock:
*/
try_to_freeze();

- /*
- * Every stopped thread should go through this function after
- * waking up. Check to see if we should notify the parent.
- */
- if (unlikely(current->signal->flags & SIGNAL_NOTIFY_CONT)) {
- read_lock(&tasklist_lock);
- do_notify_parent_cldstop(current, CLD_CONTINUED);
- read_unlock(&tasklist_lock);
- }
+ notify_parent_cont();

spin_lock_irq(&sighand->siglock);

@@ -2073,8 +2078,11 @@ relock:
if (signr != SIGKILL) {
signr = ptrace_signal(signr, info,
regs, cookie);
- if (!signr)
- continue;
+ if (!signr) {
+ /* siglock was released, restart */
+ spin_unlock_irq(&sighand->siglock);
+ goto relock;
+ }
}

ka = &sighand->action[signr-1];
@@ -2177,6 +2185,14 @@ relock:
/* NOTREACHED */
}
spin_unlock_irq(&sighand->siglock);
+
+ /*
+ * If ptrace_signal() returned a non-zero signal, control can reach
+ * here without other pending signals or going through relocking
+ * and a CONT notification may be left pending. Check it.
+ */
+ notify_parent_cont();
+
return signr;
}

--
1.7.1


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