Date:   Mon, 9 Jan 2017 20:08:44 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Vaishali Thakkar <vaishali.thakkar@...cle.com>
cc:     Julia Lawall <julia.lawall@...6.fr>,
        Kees Cook <keescook@...omium.org>,
        Pengfei Wang <wpengfeinudt@...il.com>,
        Vaishali Thakkar <vthakkar1994@...il.com>,
        linux-kernel@...r.kernel.org, Michal Marek <mmarek@...e.com>,
        cocci@...teme.lip6.fr
Subject: Re: [Cocci] [PATCH] coccicheck: add a test for repeat
 copy_from_user



On Mon, 9 Jan 2017, Vaishali Thakkar wrote:

> On Tuesday 27 December 2016 11:51 PM, Julia Lawall wrote:
> > I totally dropped the ball on this.  Many thanks to Vaishali for
> > resurrecting it.
> >
> > Some changes are suggested below.
> >
> > On Tue, 26 Apr 2016, Kees Cook wrote:
> >
> > > This is usually a sign of a resized request. This adds a check for
> > > potential races or confusions. The check isn't 100% accurate, so it
> > > needs some manual review.
> > >
> > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > ---
> > >  scripts/coccinelle/tests/reusercopy.cocci | 36
> > > +++++++++++++++++++++++++++++++
> > >  1 file changed, 36 insertions(+)
> > >  create mode 100644 scripts/coccinelle/tests/reusercopy.cocci
> > >
> > > diff --git a/scripts/coccinelle/tests/reusercopy.cocci
> > > b/scripts/coccinelle/tests/reusercopy.cocci
> > > new file mode 100644
> > > index 000000000000..53645de8ae95
> > > --- /dev/null
> > > +++ b/scripts/coccinelle/tests/reusercopy.cocci
> > > @@ -0,0 +1,36 @@
> > > +/// Recopying from the same user buffer frequently indicates a pattern of
> > > +/// Reading a size header, allocating, and then re-reading an entire
> > > +/// structure. If the structure's size is not re-validated, this can lead
> > > +/// to structure or data size confusions.
> > > +///
> > > +// Confidence: Moderate
> > > +// Copyright: (C) 2016 Kees Cook, Google. License: GPLv2.
> > > +// URL: http://coccinelle.lip6.fr/
> > > +// Comments:
> > > +// Options: -no_includes -include_headers
> >
> > The options could be: --no-include --include-headers
> >
> > Actually, Coccinelle supports both, but it only officially supports the
> > -- versions.
> >
> > > +
> > > +virtual report
> > > +virtual org
> >
> > Add, the following for the *s:
> >
> > virtual context
> >
> > Then add the following rule:
> >
> > @ok@
> > position p;
> > expression src,dest;
> > @@
> >
> > copy_from_user@p(&dest, src, sizeof(dest))
> >
> > > +
> > > +@..._twice@
> > > +position p;
> >
> > Change this to:
> >
> > position p != ok.p;
> >
> > > +identifier src;
> > > +expression dest1, dest2, size1, size2, offset;
> > > +@@
> > > +
> > > +*copy_from_user(dest1, src, size1)
> > > + ... when != src = offset
> > > +     when != src += offset
>
> Here, may be we should add few more lines from Pengfei's
> script to avoid th potential FPs.

Which lines (I don't have it handy)?

julia

>
> > Add the following lines:
> >
> >      when != if (size2 > e1 || ...) { ... return ...; }
> >      when != if (size2 > e1 || ...) { ... size2 = e2 ... }
> >
> > These changes drop cases where the last argument to copy_from_usr is the
> > size of the first argument, which seems safe enough, and where there is a
> > test on the size value that can either update it or abort the function.
> > These changes only eliminate false positives, as far as I could tell.
> >
> > If it would be more convenient, I could just send the complete revised
> > patch, or whatever seems convenient.
>
> I was also thinking that probably we should also add other user space memory
> API functions. May be get_user and strncpy_from_user. Although I'm not sure
> how common it is to find such patterns for both of these functions.
>
> > thanks,
> > julia
> >
> > > +*copy_from_user@p(dest2, src, size2)
> > > +
> > > +@...ipt:python depends on org@
> > > +p << cfu_twice.p;
> > > +@@
> > > +
> > > +cocci.print_main("potentially dangerous second copy_from_user()",p)
> > > +
> > > +@...ipt:python depends on report@
> > > +p << cfu_twice.p;
> > > +@@
> > > +
> > > +coccilib.report.print_report(p[0],"potentially dangerous second
> > > copy_from_user()")
> > > --
> > > 2.6.3
> > >
> > >
> > > --
> > > Kees Cook
> > > Chrome OS & Brillo Security
> > >
> > _______________________________________________
> > Cocci mailing list
> > Cocci@...teme.lip6.fr
> > https://systeme.lip6.fr/mailman/listinfo/cocci
> >
>
>

Powered by blists - more mailing lists