Re: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up

From	Miklos Szeredi <miklos@szeredi.hu>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up
Date	2017-02-20 16:20 +0100
Message-ID	<tcXUR-6k9-15@gated-at.bofh.it> (permalink)
References	<tbTqh-6zb-3@gated-at.bofh.it> <tcvOV-5zi-1@gated-at.bofh.it>
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On Sun, Feb 19, 2017 at 10:14 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:

> This is one hell of a DoS vector - it's really easy to eat tons of struct
> file that way.  Preparatory parts of that series make sense on their own,
> but your "let's allocate a struct file, call ->open() and schedule that
> struct file for closing upon the exit to userland on each kernel_read()"
> is not.

Found a couple of instances of this pattern (haven't looked very hard,
possibly there's more):

nfsd_read()
cachefiles_write_page()

How come this hasn't been a problem for them?

Would flush_delayed_fput() work here?  I couldn't really find what the
locking issues with synchronous fputs were.

Thanks,
Miklos

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[PATCH 0/9] overlay: fix inconsistency of ro file after copy-up Miklos Szeredi <mszeredi@redhat.com> - 2017-02-17 17:20 +0100
  [PATCH 9/9] vfs: intercept fsync on overlay files Miklos Szeredi <mszeredi@redhat.com> - 2017-02-17 17:20 +0100
  [PATCH 8/9] vfs: use helper for calling f_op->fsync() Miklos Szeredi <mszeredi@redhat.com> - 2017-02-17 17:20 +0100
  [PATCH 4/9] vfs: intercept reads to overlay files Miklos Szeredi <mszeredi@redhat.com> - 2017-02-17 17:20 +0100
    Re: [PATCH 4/9] vfs: intercept reads to overlay files Al Viro <viro@ZenIV.linux.org.uk> - 2017-02-19 10:10 +0100
      Re: [PATCH 4/9] vfs: intercept reads to overlay files Miklos Szeredi <mszeredi@redhat.com> - 2017-02-19 10:30 +0100
    Re: [PATCH 4/9] vfs: intercept reads to overlay files "zhangyi (F)" <yi.zhang@huawei.com> - 2017-02-20 09:10 +0100
      Re: [PATCH 4/9] vfs: intercept reads to overlay files Miklos Szeredi <miklos@szeredi.hu> - 2017-02-20 10:00 +0100
  Re: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up Al Viro <viro@ZenIV.linux.org.uk> - 2017-02-19 10:20 +0100
    Re: [PATCH 0/9] overlay: fix inconsistency of ro file after copy-up Miklos Szeredi <miklos@szeredi.hu> - 2017-02-20 16:20 +0100

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