From: Willem de Bruijn
> Sent: 10 March 2022 22:43
>
> On Thu, Mar 10, 2022 at 5:30 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
> >
> > On Thu, 10 Mar 2022 14:13:28 -0800 Tadeusz Struk wrote:
> > > diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> > > index 4788f6b37053..6d45112322a0 100644
> > > --- a/net/ipv6/ip6_output.c
> > > +++ b/net/ipv6/ip6_output.c
> > > @@ -1649,6 +1649,16 @@ static int __ip6_append_data(struct sock *sk,
> > > skb->protocol = htons(ETH_P_IPV6);
> > > skb->ip_summed = csummode;
> > > skb->csum = 0;
> > > +
> > > + /*
> > > + * Check if there is still room for payload
> > > + */
> >
> > TBH I think the check is self-explanatory. Not worth a banner comment,
> > for sure.
> >
> > > + if (fragheaderlen >= mtu) {
> > > + err = -EMSGSIZE;
> > > + kfree_skb(skb);
> > > + goto error;
> > > + }
> >
> > Not sure if Willem prefers this placement, but seems like we can lift
> > this check out of the loop, as soon as fragheaderlen and mtu are known.
> >
> > > /* reserve for fragmentation and ipsec header */
> > > skb_reserve(skb, hh_len + sizeof(struct frag_hdr) +
> > > dst_exthdrlen);
>
> Just updating this boundary check will do?
>
> if (mtu < fragheaderlen ||
> ((mtu - fragheaderlen) & ~7) + fragheaderlen <
> sizeof(struct frag_hdr))
> goto emsgsize;
Both those < should be <=
But I think I'd check:
if (fragheaderlen >= 1280 - sizeof (struct frag_hdr))
goto emsgsize;
first (or only!)
David
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