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Date: Tue, 10 Aug 2021 11:33:04 +0200 From: Guillaume Nault <gnault@...hat.com> To: Jakub Kicinski <kuba@...nel.org> Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org, Martin Varghese <martin.varghese@...ia.com>, Willem de Bruijn <willemb@...gle.com> Subject: Re: [PATCH net] bareudp: Fix invalid read beyond skb's linear data On Mon, Aug 09, 2021 at 09:19:18AM -0700, Jakub Kicinski wrote: > On Sun, 8 Aug 2021 18:16:25 +0200 Guillaume Nault wrote: > > On Fri, Aug 06, 2021 at 04:22:34PM -0700, Jakub Kicinski wrote: > > > On Fri, 6 Aug 2021 17:52:06 +0200 Guillaume Nault wrote: > > > > Data beyond the UDP header might not be part of the skb's linear data. > > > > Use skb_copy_bits() instead of direct access to skb->data+X, so that > > > > we read the correct bytes even on a fragmented skb. > > > > > > > > Fixes: 4b5f67232d95 ("net: Special handling for IP & MPLS.") > > > > Signed-off-by: Guillaume Nault <gnault@...hat.com> > > > > --- > > > > drivers/net/bareudp.c | 16 +++++++++++----- > > > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c > > > > index a7ee0af1af90..54e321a695ce 100644 > > > > --- a/drivers/net/bareudp.c > > > > +++ b/drivers/net/bareudp.c > > > > @@ -71,12 +71,18 @@ static int bareudp_udp_encap_recv(struct sock *sk, struct sk_buff *skb) > > > > family = AF_INET6; > > > > > > > > if (bareudp->ethertype == htons(ETH_P_IP)) { > > > > - struct iphdr *iphdr; > > > > + __u8 ipversion; > > > > > > > > - iphdr = (struct iphdr *)(skb->data + BAREUDP_BASE_HLEN); > > > > - if (iphdr->version == 4) { > > > > - proto = bareudp->ethertype; > > > > - } else if (bareudp->multi_proto_mode && (iphdr->version == 6)) { > > > > + if (skb_copy_bits(skb, BAREUDP_BASE_HLEN, &ipversion, > > > > + sizeof(ipversion))) { > > > > > > No preference just curious - could skb_header_pointer() be better suited? > > > > I have no preference either. I just used skb_copy_bits() because it > > didn't seem useful to get a pointer to the buffer (just to read one > > byte of data). > > Right, the advantage would be in the "fast" case of skb_header_pointer() > being inlined. Yes indeed. The problem was found because of some automated functionnal tests, not because of any practical use cases. So I didn't consider the possible performance differences. I see that you've applied the patch as is already. I can switch to skb_header_pointer() in the future, if anyone sees any practical benefit for it. Thanks for the review.
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