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From: Oleg Nesterov <oleg@redhat.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Sargun Dhillon <sargun@sargun.me>,
	linux-kernel@vger.kernel.org,
	containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
	tycho@tycho.ws
Subject: Re: [RFC PATCH] ptrace: add PTRACE_GETFD request
Date: Fri, 6 Dec 2019 13:23:11 +0100	[thread overview]
Message-ID: <20191206122311.GA820@redhat.com> (raw)
In-Reply-To: <20191206082539.gmefytwu3ylixj5d@wittgenstein>

> On Thu, Dec 05, 2019 at 11:44:53PM +0000, Sargun Dhillon wrote:
>
> > +static int ptrace_getfd(struct task_struct *child, unsigned long fd)
> > +{
> > +	struct files_struct *files;
> > +	struct file *file;
> > +	int ret = 0;
> > +
> > +	files = get_files_struct(child);
> > +	if (!files)
> > +		return -ENOENT;
> > +
> > +	spin_lock(&files->file_lock);
> > +	file = fcheck_files(files, fd);
> > +	if (!file)
> > +		ret = -EBADF;
> > +	else
> > +		get_file(file);
> > +	spin_unlock(&files->file_lock);
> > +	put_files_struct(files);

may be someone can finally create a helper for this, it can have more users.
say,
	struct file *get_task_file(task, fd)
	{
		struct file *file = NULL;

		task_lock(task);
		rcu_read_lock();
		if (task->files) {
			file = fcheck_files(task->files, fd);
			if (file)
				get_file(file);
		}
		rcu_read_unlock();
		task_unlock(task);

		return file;
	}


no need to get/put files_struct, no need to take ->file_lock.

> > +
> > +	if (ret)
> > +		goto out;
> > +
> > +	ret = get_unused_fd_flags(0);
> > +	if (ret >= 0)
> > +		fd_install(ret, file);
> > +
> > +	fput(file);

this looks wrong or I am totally confused...

	if (ret >= 0)
		fd_install(file);
	else
		fput(file);

?

> > @@ -1265,7 +1299,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
> >  	}
> >  
> >  	ret = ptrace_check_attach(child, request == PTRACE_KILL ||
> > -				  request == PTRACE_INTERRUPT);
> > +				  request == PTRACE_INTERRUPT ||
> > +				  request == PTRACE_GETFD);

Hmm. not sure why do you want this... But OK, we do not need to stop the tracee.

Oleg.


  reply	other threads:[~2019-12-06 12:23 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05 23:44 Sargun Dhillon
2019-12-06  2:38 ` Jann Horn
2019-12-06  6:16   ` Sargun Dhillon
2019-12-06  6:52     ` Aleksa Sarai
2019-12-06  8:25 ` Christian Brauner
2019-12-06 12:23   ` Oleg Nesterov [this message]
2019-12-06 14:10 ` Tycho Andersen
2019-12-06 19:03   ` Sargun Dhillon
2019-12-06 19:05     ` Jann Horn
2019-12-06 19:05       ` Jann Horn
2019-12-06 20:45 ` Andy Lutomirski

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