Re: [PATCH net 1/2] ioam6: fix write to cloned skb in ipv6_hop_ioam()

[Justin Iurman]

On 2/19/24 10:05, Paolo Abeni wrote:
> On Sat, 2024-02-17 at 00:43 +0100, Justin Iurman wrote:
> > ioam6_fill_trace_data() writes inside the skb payload without ensuring
> > it's writeable (e.g., not cloned). This function is called both from the
> > input and output path. The output path (ioam6_iptunnel) already does the
> > check. This commit provides a fix for the input path, inside
> > ipv6_hop_ioam().
> >
> > Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace ")
> > Reported-by: Paolo Abeni <pabeni@xxxxxxxxxx>
> > Signed-off-by: Justin Iurman <justin.iurman@xxxxxxxxx>
> > ---
> >   net/ipv6/exthdrs.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> > index 4952ae792450..f68e5faab3aa 100644
> > --- a/net/ipv6/exthdrs.c
> > +++ b/net/ipv6/exthdrs.c
> > @@ -943,6 +943,14 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
> >   		if (!skb_valid_dst(skb))
> >   			ip6_route_input(skb);
> >   
> > +		if (skb_cloned(skb)) {
> > +			if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
> > +				goto drop;
>
> My personal preference would be for using skb_ensure_writable() here,
> with write_len == optoff + hdr->opt_len.

OK, will do!

> > +
> > +			hdr = (struct ioam6_hdr *)(skb_network_header(skb) + optoff);
> > +			trace = (struct ioam6_trace_hdr *)((u8 *)hdr + sizeof(*hdr));
>
> Note that this can potentially change the network header ptr and the
> caller - ip6_parse_tlv() - has cached such value in 'nh'. You also need
> to update ip6_parse_tlv() to reload such pointer.

+1, I completely missed it, thanks!

> Side note: a bunch of self-tests are apparently stuck after this
> series. I think it's an unrelated problem. I'll try to have a better
> look.

Can you share the config to observe such behavior? I'll try to 
investigate too.

> Cheers,
>
> Paolo