linux-kernel - Re: [PATCH v10 06/12] fs, arm64: untag user pointers in copy_mount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAeHK+wLm7zSUC8dJv3LgdyvpkBN8u_24ene6b91PgM570VWbQ@mail.gmail.com>
Date:   Tue, 26 Feb 2019 15:35:40 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.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>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v10 06/12] fs, arm64: untag user pointers in copy_mount_options

On Sat, Feb 23, 2019 at 12:03 AM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 2/22/19 4:53 AM, Andrey Konovalov wrote:
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -2730,7 +2730,7 @@ 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 would have thought that copy_from_user() *is* entirely capable of
> detecting and returning an error in the case that its arguments cross
> TASK_SIZE.  It will fail and return an error, but that's what it's
> supposed to do.
>
> I'd question why this code needs to be doing its own checking in the
> first place.  Is there something subtle going on?

The comment above exact_copy_from_user() states:

Some copy_from_user() implementations do not return the exact number of
bytes remaining to copy on a fault.  But copy_mount_options() requires that.
Note that this function differs from copy_from_user() in that it will oops
on bad values of `to', rather than returning a short copy.