linux-kernel - Re: [PATCH v2] pipe: limit the per-user amount of pages allocated in pipes

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Message-Id: <201601120119.JHB51017.JFOFtSOLOMHVFQ@I-love.SAKURA.ne.jp>
Date:	Tue, 12 Jan 2016 01:19:00 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	w@....eu, viro@...iv.linux.org.uk
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, socketpair@...il.com
Subject: Re: [PATCH v2] pipe: limit the per-user amount of pages allocated in pipes

Willy Tarreau wrote:
> @@ -1066,7 +1094,8 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
>  		if (!nr_pages)
>  			goto out;
>  
> -		if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
> +		if (!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN) &&
> +		    (size > pipe_max_size || too_many_pipe_buffers(pipe->user))) {
>  			ret = -EPERM;
>  			goto out;
>  		}

I think we should not check capable(CAP_SYS_ADMIN) for size > pipe_max_size
case, for checking capable(CAP_SYS_ADMIN) needlessly generates audit logs and
also loosens permission required for setting size > pipe_max_size.

Also, I think we should not check capable(CAP_SYS_ADMIN) unless
too_many_pipe_buffers(pipe->user) is true, for checking capable(CAP_SYS_ADMIN)
needlessly generates audit logs.

Since too_many_unix_fds() requires capable(CAP_SYS_ADMIN) || capable(CAP_SYS_ADMIN),
I think what we want is something like below?

  if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
  	ret = -EPERM;
  	goto out;
  } else if (too_many_pipe_buffers(pipe->user) &&
  	     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
  	ret = -EPERM;
  	goto out;
  }