LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Miklos Szeredi <miklos@szeredi.hu>
To: Kees Cook <keescook@chromium.org>
Cc: Alexander Potapenko <glider@google.com>,
	Vivek Goyal <vgoyal@redhat.com>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-kernel@vger.kernel.org, royyang@google.com,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH] ovl: explicitly initialize error in ovl_copy_xattr()
Date: Fri, 5 Jun 2020 11:54:27 +0200
Message-ID: <CAJfpegsNL17k+Yv1-4bmogqjzq-rO9H1xT-+DM2m7qq7oH25MQ@mail.gmail.com> (raw)
In-Reply-To: <202006040844.C50B47699@keescook>

On Thu, Jun 4, 2020 at 5:57 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Jun 04, 2020 at 10:42:45AM +0200, glider@google.com wrote:
> > Under certain circumstances (we found this out running Docker on a
> > Clang-built kernel with CONFIG_INIT_STACK_ALL) ovl_copy_xattr() may
> > return uninitialized value of |error| from ovl_copy_xattr().
> > It is then returned by ovl_create() to lookup_open(), which casts it to
> > an invalid dentry pointer, that can be further read or written by the
> > lookup_open() callers.
> >
> > The uninitialized value is returned when all the xattr on the file
> > are ovl_is_private_xattr(), which is actually a successful case,
> > therefore we initialize |error| with 0.
> >
> > Signed-off-by: Alexander Potapenko <glider@google.com>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Roy Yang <royyang@google.com>
> > Cc: <stable@vger.kernel.org> # 4.1
>
> Please include a Fixes (more below) and Link tags for details to help
> guide backporting, then you don't need to bother with with "# 4.1",
> the -stable tools will figure it out with a "Fixes" tag.
>
> Thanks for the v2!
>
> Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
> > The bug seem to date back to at least v4.1 where the annotation has been
> > introduced (i.e. the compilers started noticing error could be used
> > before being initialized). I hovever didn't try to prove that the
> > problem is actually reproducible on such ancient kernels. We've seen it
> > on a real machine running v4.4 as well.
>
> It seems like it came from this, but that's v4.5:
>
> Fixes: e4ad29fa0d22 ("ovl: use a minimal buffer in ovl_copy_xattr")


I believe it's actually:

Fixes: 0956254a2d5b ("ovl: don't copy up opaqueness")

That patch added the ovl_is_private_xattr() check in ovl_copy_xattr(),
without which 'error' was always initilalized.

Thanks,
Miklos

  parent reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04  8:42 glider
2020-06-04  8:57 ` Miklos Szeredi
2020-06-04 16:00   ` Kees Cook
2020-06-04 15:57 ` Kees Cook
2020-06-05  9:46   ` Alexander Potapenko
2020-06-05  9:54   ` Miklos Szeredi [this message]
  -- strict thread matches above, loose matches on Subject: below --
2020-06-03 17:47 glider
2020-06-03 20:35 ` Kees Cook
2020-06-03 21:46 ` Vivek Goyal
2020-06-04  8:28   ` Alexander Potapenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAJfpegsNL17k+Yv1-4bmogqjzq-rO9H1xT-+DM2m7qq7oH25MQ@mail.gmail.com \
    --to=miklos@szeredi.hu \
    --cc=glider@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-unionfs@vger.kernel.org \
    --cc=royyang@google.com \
    --cc=stable@vger.kernel.org \
    --cc=vgoyal@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git