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Commit dcace06c authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

ptrace: mv send-SIGSTOP from do_fork() to ptrace_init_task() 



If the new child is traced, do_fork() adds the pending SIGSTOP.
It assumes that either it is traced because of auto-attach or the
tracer attached later, in both cases sigaddset/set_thread_flag is
correct even if SIGSTOP is already pending.

Now that we have PTRACE_SEIZE this is no longer right in the latter
case. If the tracer does PTRACE_SEIZE after copy_process() makes the
child visible the queued SIGSTOP is wrong.

We could check PT_SEIZED bit and change ptrace_attach() to set both
PT_PTRACED and PT_SEIZED bits simultaneously but see the next patch,
we need to know whether this child was auto-attached or not anyway.

So this patch simply moves this code to ptrace_init_task(), this
way we can never race with ptrace_attach().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarTejun Heo <tj@kernel.org>
parent 6634ae10

include/linux/ptrace.h

+3 −0
Original line number Diff line number Diff line
@@ -227,6 +227,9 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace) 
	if (unlikely(ptrace) && current->ptrace) {

		child->ptrace = current->ptrace;

		__ptrace_link(child, current->parent);



		sigaddset(&child->pending.signal, SIGSTOP);

		set_tsk_thread_flag(child, TIF_SIGPENDING);

	}

}

kernel/fork.c

+0 −12
Original line number Diff line number Diff line
@@ -37,7 +37,6 @@ 
#include <linux/swap.h>

#include <linux/syscalls.h>

#include <linux/jiffies.h>

#include <linux/tracehook.h>

#include <linux/futex.h>

#include <linux/compat.h>

#include <linux/kthread.h>
@@ -1521,17 +1520,6 @@ long do_fork(unsigned long clone_flags, 


		audit_finish_fork(p);



		/*

		 * Child is ready but hasn't started running yet.  Queue

		 * SIGSTOP if it's gonna be ptraced - it doesn't matter who

		 * attached/attaching to this task, the pending SIGSTOP is

		 * right in any case.

		 */

		if (unlikely(p->ptrace)) {

			sigaddset(&p->pending.signal, SIGSTOP);

			set_tsk_thread_flag(p, TIF_SIGPENDING);

		}



		/*

		 * We set PF_STARTING at creation in case tracing wants to

		 * use this to distinguish a fully live task from one that