netdev - Re: [PATCH v7 3/9] net/scm: Regularize compat handling of scm_detach

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Message-ID: <202008071516.83432C389@keescook>
Date:   Fri, 7 Aug 2020 15:18:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Laight <David.Laight@...lab.com>,
        Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>,
        Matt Denton <mpdenton@...gle.com>,
        Jann Horn <jannh@...gle.com>, Chris Palmer <palmer@...gle.com>,
        Robert Sesek <rsesek@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        containers@...ts.linux-foundation.org, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Amit Pundir <amit.pundir@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH v7 3/9] net/scm: Regularize compat handling of
 scm_detach_fds()

On Fri, Aug 07, 2020 at 01:29:24PM -0700, John Stultz wrote:
> On Thu, Jul 9, 2020 at 11:28 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > Duplicate the cleanups from commit 2618d530dd8b ("net/scm: cleanup
> > scm_detach_fds") into the compat code.
> >
> > Replace open-coded __receive_sock() with a call to the helper.
> >
> > Move the check added in commit 1f466e1f15cf ("net: cleanly handle kernel
> > vs user buffers for ->msg_control") to before the compat call, even
> > though it should be impossible for an in-kernel call to also be compat.
> >
> > Correct the int "flags" argument to unsigned int to match fd_install()
> > and similar APIs.
> >
> > Regularize any remaining differences, including a whitespace issue,
> > a checkpatch warning, and add the check from commit 6900317f5eff ("net,
> > scm: fix PaX detected msg_controllen overflow in scm_detach_fds") which
> > fixed an overflow unique to 64-bit. To avoid confusion when comparing
> > the compat handler to the native handler, just include the same check
> > in the compat handler.
> >
> > Acked-by: Christian Brauner <christian.brauner@...ntu.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> 
> Hey Kees,
>   So during the merge window (while chasing a few other regressions),
> I noticed occasionally my Dragonboard 845c running AOSP having trouble
> with the web browser crashing or other apps hanging, and I've bisected
> the issue down to this change.
> 
> Unfortunately it doesn't revert cleanly so I can't validate reverting
> it sorts things against linus/HEAD.  Anyway, I wanted to check and see
> if you had any other reports of similar or any ideas what might be
> going wrong?

Hi; Yes, sorry for the trouble. I had a typo in a refactor of
SCM_RIGHTS. I suspect it'll be fixed by this:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1fa2c0a0c814fbae0eb3e79a510765225570d043

Can you verify Linus's latest tree works for you? If not, there might be
something else hiding in the corners...

Thanks!

-- 
Kees Cook