linux-kernel - [PATCH] ptrace: clear TIF_SYSCALL

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Date:   Thu,  1 Sep 2016 15:54:36 +0200
From:   Ales Novak <alnovak@...e.cz>
To:     linux-kernel@...r.kernel.org
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ales Novak <alnovak@...e.cz>, Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH] ptrace: clear TIF_SYSCALL_TRACE on ptrace detach

On ptrace_detach(), 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.

Signed-off-by: Ales Novak <alnovak@...e.cz>
Cc: Jiri Kosina <jkosina@...e.cz>
---
 kernel/ptrace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 1d3b766..634740f 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -85,6 +85,7 @@ void __ptrace_unlink(struct task_struct *child)
 	task_clear_jobctl_pending(child, JOBCTL_TRAP_MASK);
 	task_clear_jobctl_trapping(child);
 
+	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 	/*
 	 * Reinstate JOBCTL_STOP_PENDING if group stop is in effect and
 	 * @child isn't dead.
-- 
2.7.0