ptrace: mv send-SIGSTOP from do_fork() to ptrace_init_task() (dcace06c) · Commits · 戴 / test

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:

Oleg Nesterov <oleg@redhat.com> Acked-by:

Tejun Heo <tj@kernel.org>

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

Admin message