proc: restrict access to /proc/PID/io

/proc/PID/io may be used for gathering private information.  E.g.  for
openssh and vsftpd daemons wchars/rchars may be used to learn the
precise password length.  Restrict it to processes being able to ptrace
the target process.

ptrace_may_access() is needed to prevent keeping open file descriptor of
"io" file, executing setuid binary and gathering io information of the
setuid'ed process.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
	unsigned int nr;
	struct task_struct *reaper;
	struct tgid_iter iter;
	struct pid_namespace *ns;

	if (filp->f_pos >= PID_MAX_LIMIT + TGID_OFFSET)
		goto out_no_task;
	nr = filp->f_pos - FIRST_PROCESS_ENTRY;

	reaper = get_proc_task(filp->f_path.dentry->d_inode);
	if (!reaper)
		goto out_no_task;

	for (; nr < ARRAY_SIZE(proc_base_stuff); filp->f_pos++, nr++) {
		const struct pid_entry *p = &proc_base_stuff[nr];
		if (proc_base_fill_cache(filp, dirent, filldir, reaper, p) < 0)
			goto out;
	}

	ns = filp->f_dentry->d_sb->s_fs_info;
	iter.task = NULL;
	iter.tgid = filp->f_pos - TGID_OFFSET;
	for (iter = next_tgid(ns, iter);
	     iter.task;
	     iter.tgid += 1, iter = next_tgid(ns, iter)) {
		filp->f_pos = iter.tgid + TGID_OFFSET;
		if (proc_pid_fill_cache(filp, dirent, filldir, iter) < 0) {
			put_task_struct(iter.task);
			goto out;
		}
	}
	filp->f_pos = PID_MAX_LIMIT + TGID_OFFSET;
out:
	put_task_struct(reaper);
out_no_task:
	return 0;
}

int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
	unsigned int nr;
	struct task_struct *reaper;
	struct tgid_iter iter;
	struct pid_namespace *ns;

	if (filp->f_pos >= PID_MAX_LIMIT + TGID_OFFSET)
		goto out_no_task;
	nr = filp->f_pos - FIRST_PROCESS_ENTRY;

	reaper = get_proc_task(filp->f_path.dentry->d_inode);
	if (!reaper)
		goto out_no_task;

	for (; nr < ARRAY_SIZE(proc_base_stuff); filp->f_pos++, nr++) {
		const struct pid_entry *p = &proc_base_stuff[nr];
		if (proc_base_fill_cache(filp, dirent, filldir, reaper, p) < 0)
			goto out;
	}

	ns = filp->f_dentry->d_sb->s_fs_info;
	iter.task = NULL;
	iter.tgid = filp->f_pos - TGID_OFFSET;
	for (iter = next_tgid(ns, iter);
	     iter.task;
	     iter.tgid += 1, iter = next_tgid(ns, iter)) {
		filp->f_pos = iter.tgid + TGID_OFFSET;
		if (proc_pid_fill_cache(filp, dirent, filldir, iter) < 0) {
			put_task_struct(iter.task);
			goto out;
		}
	}
	filp->f_pos = PID_MAX_LIMIT + TGID_OFFSET;
out:
	put_task_struct(reaper);
out_no_task:
	return 0;
}
