[ovs-dev] [PATCH] expr: Disallow < <= >= > comparisons against empty value set.

[Ben Pfaff]

Thanks, applied and backported.

On Thu, Oct 11, 2018 at 01:08:43PM -0700, Yifeng Sun wrote:
> Looks good to me, thanks.
> 
> Reviewed-by: Yifeng Sun <pkusunyifeng at gmail.com>
> 
> On Thu, Oct 11, 2018 at 12:44 PM Ben Pfaff <blp at ovn.org> wrote:
> 
> > OVN expression syntax does not allow a literal empty value set, like {}.
> > Rather, any literal value set has to have at least one value.  However,
> > value sets that originate from address sets or from port groups can be
> > empty.  In such a case, == and != comparisons are allowed but < <= >= >
> > should be errors.  The actual implementation failed to properly disallow
> > the latter and instead tried to access the first element of the value set,
> > a bad read.  This fixes the problem.
> >
> > Reported-at: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10731
> > Reported-at
> > <https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10731Reported-at>:
> > https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10767
> > Signed-off-by
> > <https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10767Signed-off-by>:
> > Ben Pfaff <blp at ovn.org>
> > ---
> >  ovn/lib/expr.c | 5 +++++
> >  tests/ovn.at   | 2 ++
> >  2 files changed, 7 insertions(+)
> >
> > diff --git a/ovn/lib/expr.c b/ovn/lib/expr.c
> > index 148ac869e861..16dd1776b543 100644
> > --- a/ovn/lib/expr.c
> > +++ b/ovn/lib/expr.c
> > @@ -578,6 +578,11 @@ make_cmp(struct expr_context *ctx,
> >                          f->symbol->name);
> >              goto exit;
> >          }
> > +        if (!cs->n_values) {
> > +            lexer_error(ctx->lexer, "Only == and != operators may be used
> > "
> > +                        "to compare a field against an empty value set.");
> > +            goto exit;
> > +        }
> >          if (cs->values[0].masked) {
> >              lexer_error(ctx->lexer, "Only == and != operators may be used
> > "
> >                          "with masked constants.  Consider using subfields
> > "
> > diff --git a/tests/ovn.at b/tests/ovn.at
> > index 44475175d20a..94676a9aa802 100644
> > --- a/tests/ovn.at
> > +++ b/tests/ovn.at
> > @@ -351,6 +351,8 @@ eth.dst[40] x => Syntax error at `x' expecting end of
> > input.
> >
> >  ip4.src == {1.2.3.4, $set1, $unknownset} => Syntax error at `$unknownset'
> > expecting address set name.
> >  eth.src == {$set3, badmac, 00:00:00:00:00:01} => Syntax error at `badmac'
> > expecting constant.
> > +
> > +ct_label > $set4 => Only == and != operators may be used to compare a
> > field against an empty value set.
> >  ]])
> >  sed 's/ =>.*//' test-cases.txt > input.txt
> >  sed 's/.* => //' test-cases.txt > expout
> > --
> > 2.16.1
> >
> > _______________________________________________
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> > dev at openvswitch.org
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> >