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From: Ales Novak <>
To: Oleg Nesterov <>
	Andrew Morton <>,
	Jiri Kosina <>, Ales Novak <>
Subject: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach
Date: Thu,  1 Sep 2016 21:51:33 +0200
Message-ID: <> (raw)
In-Reply-To: <>

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

Signed-off-by: Ales Novak <>
Cc: Jiri Kosina <>
 kernel/ptrace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 1d3b766..2a99027 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -73,6 +73,8 @@ void __ptrace_unlink(struct task_struct *child)
+	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 	child->parent = child->real_parent;
@@ -489,7 +491,6 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
 	/* Architecture-specific hardware disable .. */
-	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);

  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-01 13:54 Ales Novak
2016-09-01 16:46 ` Oleg Nesterov
2016-09-01 19:50   ` Ales Novak
2016-09-01 19:51   ` Ales Novak [this message]
2016-09-02 12:25     ` Oleg Nesterov

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