Subject: Re: [PATCH iproute2] lib/libnetlink: fix response seq check

From: Stephen Hemminger <[email-masked]>
Date: Wed, 3 Oct 2018 16:50:31 -0700

On Wed, 3 Oct 2018 16:01:40 -0700
Vlad Dumitrescu <[email-masked]> wrote:

> Hi,
> 
> On Fri, Sep 28, 2018 at 10:14 AM <[email-masked]> wrote:
> >
> > From: Vlad Dumitrescu <[email-masked]>
> >
> > Taking a one-iovec example, with rtnl->seq at 42. iovlen == 1, seq
> > becomes 43 on line 604, and a message is sent with nlmsg_seq == 43. If
> > a response with nlmsg_seq of 42 is received, the condition being fixed
> > in this patch would incorrectly accept it.
> >
> > Fixes: 72a2ff3916e5 ("lib/libnetlink: Add a new function rtnl_talk_iov")
> > Signed-off-by: Vlad Dumitrescu <[email-masked]>
> > ---
> >  lib/libnetlink.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/libnetlink.c b/lib/libnetlink.c
> > index f18dceac..4d2416bf 100644
> > --- a/lib/libnetlink.c
> > +++ b/lib/libnetlink.c
> > @@ -647,7 +647,7 @@ static int __rtnl_talk_iov(struct rtnl_handle *rtnl, struct iovec *iov,
> >
> >                         if (nladdr.nl_pid != 0 ||
> >                             h->nlmsg_pid != rtnl->local.nl_pid ||
> > -                           h->nlmsg_seq > seq || h->nlmsg_seq < seq - iovlen) {
> > +                           h->nlmsg_seq > seq || h->nlmsg_seq < seq - iovlen + 1) {
> >                                 /* Don't forget to skip that message. */
> >                                 status -= NLMSG_ALIGN(len);
> >                                 h = (struct nlmsghdr *)((char *)h + NLMSG_ALIGN(len));
> > --
> > 2.19.0.605.g01d371f741-goog  
> 
> Did anybody get a chance to review this? I'm not 100% sure I'm fixing
> the right thing.
> 
> Thanks,
> Vlad

Could you give an example where this failed.
Better yet one of the tests.