uglify kill_pid_info() to fix kill() vs exec() race (d36174bc) · Commits · 戴 / test

kill_pid_info()->pid_task() could be the old leader of the execing process. In that case it is possible that the leader will be released before we take siglock. This means that kill_pid_info() (and thus sys_kill()) can return a false -ESRCH. Change the code to retry when lock_task_sighand() fails. The endless loop is not possible, __exit_signal() both clears ->sighand and does detach_pid(). Signed-off-by:

Oleg Nesterov <oleg@tv-sign.ru> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Davide Libenzi <davidel@xmailserver.org> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Roland McGrath <roland@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

+12 −3

Original line number	Original line	Diff line number	Diff line
	@@ -1050,17 +1050,26 @@ int kill_pgrp_info(int sig, struct siginfo info, struct pid pgrp)

	int kill_pid_info(int sig, struct siginfo info, struct pid pid)		int kill_pid_info(int sig, struct siginfo info, struct pid pid)
	{		{
	int error;		int error = -ESRCH;
	struct task_struct *p;		struct task_struct *p;

	rcu_read_lock();		rcu_read_lock();
	if (unlikely(sig_needs_tasklist(sig)))		if (unlikely(sig_needs_tasklist(sig)))
	read_lock(&tasklist_lock);		read_lock(&tasklist_lock);

			retry:
	p = pid_task(pid, PIDTYPE_PID);		p = pid_task(pid, PIDTYPE_PID);
	error = -ESRCH;		if (p) {
	if (p)
	error = group_send_sig_info(sig, info, p);		error = group_send_sig_info(sig, info, p);
			if (unlikely(error == -ESRCH))
			/*
			* The task was unhashed in between, try again.
			* If it is dead, pid_task() will return NULL,
			* if we race with de_thread() it will find the
			* new leader.
			*/
			goto retry;
			}

	if (unlikely(sig_needs_tasklist(sig)))		if (unlikely(sig_needs_tasklist(sig)))
	read_unlock(&tasklist_lock);		read_unlock(&tasklist_lock);

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