linux-kernel - Re: [PATCH] ovl: explicitly initialize error in ovl_copy

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Date:   Wed, 3 Jun 2020 13:35:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     glider@...gle.com
Cc:     miklos@...redi.hu, linux-unionfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, royyang@...gle.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] ovl: explicitly initialize error in ovl_copy_xattr()

On Wed, Jun 03, 2020 at 07:47:14PM +0200, glider@...gle.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@...gle.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@...r.kernel.org
Reviewed-by: Kees Cook <keescook@...omium.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