linux-kernel - Re: [PATCH v18 07/15] fs/namespace: untag user pointers in copy_mount

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Message-ID: <CAAeHK+x2TL057Fr0K7FZBTYgeEPVU3cC6scEeiSYk-Jkb3xgfg@mail.gmail.com>
Date:   Mon, 15 Jul 2019 18:00:04 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-rdma@...r.kernel.org, linux-media@...r.kernel.org,
        kvm@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH v18 07/15] fs/namespace: untag user pointers in copy_mount_options

On Mon, Jun 24, 2019 at 7:50 PM Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Mon, Jun 24, 2019 at 04:32:52PM +0200, Andrey Konovalov wrote:
> > This patch is a part of a series that extends kernel ABI to allow to pass
> > tagged user pointers (with the top byte set to something else other than
> > 0x00) as syscall arguments.
> >
> > In copy_mount_options a user address is being subtracted from TASK_SIZE.
> > If the address is lower than TASK_SIZE, the size is calculated to not
> > allow the exact_copy_from_user() call to cross TASK_SIZE boundary.
> > However if the address is tagged, then the size will be calculated
> > incorrectly.
> >
> > Untag the address before subtracting.
> >
> > Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>
> > Reviewed-by: Vincenzo Frascino <vincenzo.frascino@....com>
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> > Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > ---
> >  fs/namespace.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/namespace.c b/fs/namespace.c
> > index 7660c2749c96..ec78f7223917 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -2994,7 +2994,7 @@ void *copy_mount_options(const void __user * data)
> >        * the remainder of the page.
> >        */
> >       /* copy_from_user cannot cross TASK_SIZE ! */
> > -     size = TASK_SIZE - (unsigned long)data;
> > +     size = TASK_SIZE - (unsigned long)untagged_addr(data);
> >       if (size > PAGE_SIZE)
> >               size = PAGE_SIZE;
>
> I think this patch needs an ack from Al Viro (cc'ed).
>
> --
> Catalin

Hi Al,

Could you take a look and give your acked-by?

Thanks!