ptrace: PTRACE_LISTEN forgets to unlock ->siglock

If PTRACE_LISTEN fails after lock_task_sighand() it doesn't drop ->siglock.

Reported-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 13 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 9de3ecfd20f9..a70d2a5d8c7b 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -744,20 +744,17 @@ int ptrace_request(struct task_struct *child, long request,
                         break;
 
                 si = child->last_siginfo;
-                if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP))
-                        break;
-
-                child->jobctl |= JOBCTL_LISTENING;
-
-                /*
-                 * If NOTIFY is set, it means event happened between start
-                 * of this trap and now.  Trigger re-trap immediately.
-                 */
-                if (child->jobctl & JOBCTL_TRAP_NOTIFY)
-                        signal_wake_up(child, true);
-
+                if (likely(si && (si->si_code >> 8) == PTRACE_EVENT_STOP)) {
+                        child->jobctl |= JOBCTL_LISTENING;
+                        /*
+                         * If NOTIFY is set, it means event happened between
+                         * start of this trap and now.  Trigger re-trap.
+                         */
+                        if (child->jobctl & JOBCTL_TRAP_NOTIFY)
+                                signal_wake_up(child, true);
+                        ret = 0;
+                }
                 unlock_task_sighand(child, &flags);
-                ret = 0;
                 break;
 
         case PTRACE_DETACH:      /* detach a process that was attached. */