Re: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append_data

[Tadeusz Struk]

Hi David,
On 3/7/22 18:58, David Laight wrote:
> > diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> > index 4788f6b37053..622345af323e 100644
> > --- a/net/ipv6/ip6_output.c
> > +++ b/net/ipv6/ip6_output.c
> > @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
> >   				err = -EINVAL;
> >   				goto error;
> >   			}
> > +			if (unlikely(alloclen < fraglen)) {
> > +				if (printk_ratelimit())
> > +					pr_warn("%s: wrong alloclen: %d, fraglen: %d",
> > +						__func__, alloclen, fraglen);
> > +				alloclen = fraglen;
> > +			}
> > +
> Except that is a valid case, see a few lines higher:
>
> 				alloclen = min_t(int, fraglen, MAX_HEADER);
> 				pagedlen = fraglen - alloclen;
>
> You need to report the input values that cause the problem later on.

OK, but in this case it falls into the first if block:
https://elixir.bootlin.com/linux/v5.17-rc7/source/net/ipv6/ip6_output.c#L1606
where alloclen is assigned the value of mtu.
The values in this case are just before the alloc_skb() are:

alloclen = 1480
alloc_extra = 136
datalen = 64095
fragheaderlen = 1480
fraglen = 65575
transhdrlen = 0
mtu = 1480

--
Thanks,
Tadeusz