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From: Kees Cook <keescook@chromium.org>
To: glider@google.com
Cc: miklos@szeredi.hu, linux-unionfs@vger.kernel.org,
	linux-kernel@vger.kernel.org, royyang@google.com,
	stable@vger.kernel.org
Subject: Re: [PATCH] ovl: explicitly initialize error in ovl_copy_xattr()
Date: Wed, 3 Jun 2020 13:35:09 -0700
Message-ID: <202006031219.36197D0729@keescook> (raw)
In-Reply-To: <20200603174714.192027-1-glider@google.com>

On Wed, Jun 03, 2020 at 07:47:14PM +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.
> 
> Signed-off-by: Alexander Potapenko <glider@google.com>

Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405
Fixes: e4ad29fa0d22 ("ovl: use a minimal buffer in ovl_copy_xattr")
Cc: stable@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>

It seems the error isn't reported anywhere, so the value likely isn't
too important. -EINVAL seems sane to me.

Thought: should CONFIG_INIT_STACK_ALL=y disable uninitialized_var()?

$ git grep uninitialized_var | wc -l
300

We have evidence this is being used inappropriately and is masking bugs.
I would actually think it should should be removed globally, but it
seems especially important for CONFIG_INIT_STACK_ALL=y.

I've opened:
https://github.com/KSPP/linux/issues/81

-- 
Kees Cook

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-03 17:47 glider
2020-06-03 20:35 ` Kees Cook [this message]
2020-06-03 21:46 ` Vivek Goyal
2020-06-04  8:28   ` Alexander Potapenko
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

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