Re: [dpdk-dev] [RFC 3/5] bpf: fix validation of eal_divmod

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 7 Nov 2018 12:54:54 +0000
"Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:

> > -----Original Message-----
> > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen Hemminger
> > Sent: Tuesday, November 6, 2018 9:49 PM
> > To: dev@dpdk.org
> > Cc: Stephen Hemminger <stephen@networkplumber.org>
> > Subject: [dpdk-dev] [RFC 3/5] bpf: fix validation of eal_divmod
> > 
> > Coverity spotted self assignment in BPF eval_divmod.  
> 
> Yep, there is one.
> As I remember I have to add it because one of old versions 
> of compiler (clang???) complained about 'variable being used uninitialized'.
> 
> > This looks like a bug where the incoming source register
> > should have been used instead.  
> 
> Nope, that's a wrong guess.
> We shouldn't do it here.
> Konstantin
> 
> > 
> > Coverity issue: 302850
> > Fixes: 8021917293d0 ("bpf: add extra validation for input BPF program")
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> >  lib/librte_bpf/bpf_validate.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/librte_bpf/bpf_validate.c b/lib/librte_bpf/bpf_validate.c
> > index 83983efc4e5c..b768f72c4c02 100644
> > --- a/lib/librte_bpf/bpf_validate.c
> > +++ b/lib/librte_bpf/bpf_validate.c
> > @@ -512,7 +512,7 @@ eval_divmod(uint32_t op, struct bpf_reg_val *rd, struct bpf_reg_val *rs,
> >  		if (op == BPF_MOD)
> >  			rd->u.max = RTE_MIN(rd->u.max, rs->u.max - 1);
> >  		else
> > -			rd->u.max = rd->u.max;
> > +			rd->u.max = rs->u.max;
> >  		rd->u.min = 0;
> >  	}
> > 
> > --
> > 2.17.1  
> 

Well it was being used unintialized, your trick of self assignment fooled clang
but did not fool Coverity.  What does the other BPF validator do?