Messages in this thread | | | From | Kees Cook <> | Date | Mon, 9 Jan 2017 12:56:02 -0800 | Subject | Re: [Cocci] [PATCH] coccicheck: add a test for repeat copy_from_user |
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On Mon, Jan 9, 2017 at 11:08 AM, Julia Lawall <julia.lawall@lip6.fr> wrote: > > > 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@chromium.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)) >> > >> > > + >> > > +@cfu_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)?
I'm going to compare https://github.com/wpengfei/double_fetch_cocci/blob/master/pattern_match_linux.cocci to my original one, add your improvements and see what I get...
-Kees
> > 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) >> > > + >> > > +@script:python depends on org@ >> > > +p << cfu_twice.p; >> > > +@@ >> > > + >> > > +cocci.print_main("potentially dangerous second copy_from_user()",p) >> > > + >> > > +@script: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@systeme.lip6.fr >> > https://systeme.lip6.fr/mailman/listinfo/cocci >> > >> >>
-- Kees Cook Nexus Security
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