ptrace: clear TIF_SYSCALL_TRACE on ptrace detach

On __ptrace_detach(), called from do_exit()->exit_notify()->
forget_original_parent()->exit_ptrace(), the TIF_SYSCALL_TRACE in
thread->flags of the tracee is not cleared up.  This results in the
tracehook_report_syscall_* being called (though there's no longer a tracer
listening to that) upon its further syscalls.

Example scenario - attach "strace" to a running process and kill it (the
strace) with SIGKILL.  You'll see that the syscall trace hooks are still
being called.

The clearing of this flag should be moved from ptrace_detach() to
__ptrace_detach().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ales Novak <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Cc: Jiri Kosina <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 1d3b7665d0be0223343530bcfc940bfa3e525c28..2a99027312a6af6773027e20029752efddc418e3 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -73,6 +73,8 @@ void __ptrace_unlink(struct task_struct *child)
 {
        BUG_ON(!child->ptrace);
 
+       clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+
        child->parent = child->real_parent;
        list_del_init(&child->ptrace_entry);
 
@@ -489,7 +491,6 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
 
        /* Architecture-specific hardware disable .. */
        ptrace_disable(child);
-       clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 
        write_lock_irq(&tasklist_lock);
        /*