On Wed, Feb 8, 2017 at 8:58 AM, Sowmini Varadhan <sowmini.varad...@oracle.com> wrote: > On (02/08/17 08:37), Willem de Bruijn wrote: >> Date: Wed, 8 Feb 2017 08:37:19 -0800 >> From: Willem de Bruijn <willemdebruijn.ker...@gmail.com> >> To: Sowmini Varadhan <sowmini.varad...@oracle.com> >> Cc: Network Development <netdev@vger.kernel.org>, David Miller >> <da...@davemloft.net>, Eric Dumazet <eric.duma...@gmail.com>, Dmitry >> Vyukov <dvyu...@google.com>, Willem de Bruijn <will...@google.com> >> Subject: Re: [PATCH net 2/2] packet: round up linear to header len >> >> On Wed, Feb 8, 2017 at 7:34 AM, Sowmini Varadhan >> <sowmini.varad...@oracle.com> wrote: >> > On (02/07/17 15:57), Willem de Bruijn wrote: >> >> @@ -2816,8 +2816,9 @@ static int packet_snd(struct socket *sock, struct >> >> msghdr *msg, size_t len) >> >> err = -ENOBUFS; >> >> hlen = LL_RESERVED_SPACE(dev); >> >> tlen = dev->needed_tailroom; >> >> - skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, >> >> - __virtio16_to_cpu(vio_le(), >> >> vnet_hdr.hdr_len), >> >> + linear = __virtio16_to_cpu(vio_le(), vnet_hdr.hdr_len); >> >> + linear = max(linear, min_t(int, len, dev->hard_header_len)); >> >> + skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, linear, >> >> msg->msg_flags & MSG_DONTWAIT, &err); >> > > : >> Do you mean the difference that it unconditionally pulls >> hard_header_len, optionally with zero padding, whereas this new >> path can check against new min_header_len and thus allows >> packets shorter than hard_header_len? > > yes, maybe it doesnt matter, becaues hard_header_len >= min_header_len > at all times
The code is not subject to this bug, so I'd rather not touch it in this fix for stable. But you raise a good point. This logic is subtle and fragile. It will be good to deduplicate across packet_snd and tpacket_snd in a follow-up to net-next.
