On Tue, Jun 18, 2024 at 5:24 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > Jiri Pirko wrote: > > Mon, Jun 17, 2024 at 09:07:58PM CEST, willemdebruijn.kernel@xxxxxxxxx wrote: > > >Jiri Pirko wrote: > > >> Mon, Jun 17, 2024 at 07:45:14AM CEST, chengen.du@xxxxxxxxxxxxx wrote: > > >> >The issue initially stems from libpcap. The ethertype will be overwritten > > >> >as the VLAN TPID if the network interface lacks hardware VLAN offloading. > > >> >In the outbound packet path, if hardware VLAN offloading is unavailable, > > >> >the VLAN tag is inserted into the payload but then cleared from the sk_buff > > >> >struct. Consequently, this can lead to a false negative when checking for > > >> >the presence of a VLAN tag, causing the packet sniffing outcome to lack > > >> >VLAN tag information (i.e., TCI-TPID). As a result, the packet capturing > > >> >tool may be unable to parse packets as expected. > > >> > > > >> >The TCI-TPID is missing because the prb_fill_vlan_info() function does not > > >> >modify the tp_vlan_tci/tp_vlan_tpid values, as the information is in the > > >> >payload and not in the sk_buff struct. The skb_vlan_tag_present() function > > >> >only checks vlan_all in the sk_buff struct. In cooked mode, the L2 header > > >> >is stripped, preventing the packet capturing tool from determining the > > >> >correct TCI-TPID value. Additionally, the protocol in SLL is incorrect, > > >> >which means the packet capturing tool cannot parse the L3 header correctly. > > >> > > > >> >Link: https://github.com/the-tcpdump-group/libpcap/issues/1105 > > >> >Link: https://lore.kernel.org/netdev/20240520070348.26725-1-chengen.du@xxxxxxxxxxxxx/T/#u > > >> >Fixes: 393e52e33c6c ("packet: deliver VLAN TCI to userspace") > > >> >Cc: stable@xxxxxxxxxxxxxxx > > >> >Signed-off-by: Chengen Du <chengen.du@xxxxxxxxxxxxx> > > >> >--- > > >> > net/packet/af_packet.c | 86 +++++++++++++++++++++++++++++++++++++++++- > > >> > 1 file changed, 84 insertions(+), 2 deletions(-) > > >> > > > >> >diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > > >> >index ea3ebc160e25..84e8884a77e3 100644 > > >> >--- a/net/packet/af_packet.c > > >> >+++ b/net/packet/af_packet.c > > >> >@@ -538,6 +538,61 @@ static void *packet_current_frame(struct packet_sock *po, > > >> > return packet_lookup_frame(po, rb, rb->head, status); > > >> > } > > >> > > > >> >+static u16 vlan_get_tci(struct sk_buff *skb, struct net_device *dev) > > >> >+{ > > >> >+ struct vlan_hdr vhdr, *vh; > > >> >+ u8 *skb_orig_data = skb->data; > > >> >+ int skb_orig_len = skb->len; > > >> >+ unsigned int header_len; > > >> >+ > > >> >+ if (!dev) > > >> >+ return 0; > > >> >+ > > >> >+ /* In the SOCK_DGRAM scenario, skb data starts at the network > > >> >+ * protocol, which is after the VLAN headers. The outer VLAN > > >> >+ * header is at the hard_header_len offset in non-variable > > >> >+ * length link layer headers. If it's a VLAN device, the > > >> >+ * min_header_len should be used to exclude the VLAN header > > >> >+ * size. > > >> >+ */ > > >> >+ if (dev->min_header_len == dev->hard_header_len) > > >> >+ header_len = dev->hard_header_len; > > >> >+ else if (is_vlan_dev(dev)) > > >> >+ header_len = dev->min_header_len; > > >> >+ else > > >> >+ return 0; > > >> >+ > > >> >+ skb_push(skb, skb->data - skb_mac_header(skb)); > > >> >+ vh = skb_header_pointer(skb, header_len, sizeof(vhdr), &vhdr); > > >> >+ if (skb_orig_data != skb->data) { > > >> >+ skb->data = skb_orig_data; > > >> >+ skb->len = skb_orig_len; > > >> >+ } > > >> >+ if (unlikely(!vh)) > > >> >+ return 0; > > >> >+ > > >> >+ return ntohs(vh->h_vlan_TCI); > > >> >+} > > >> >+ > > >> >+static __be16 vlan_get_protocol_dgram(struct sk_buff *skb) > > >> >+{ > > >> >+ __be16 proto = skb->protocol; > > >> >+ > > >> >+ if (unlikely(eth_type_vlan(proto))) { > > >> >+ u8 *skb_orig_data = skb->data; > > >> >+ int skb_orig_len = skb->len; > > >> >+ > > >> >+ skb_push(skb, skb->data - skb_mac_header(skb)); > > >> >+ proto = __vlan_get_protocol(skb, proto, NULL); > > >> >+ if (skb_orig_data != skb->data) { > > >> >+ skb->data = skb_orig_data; > > >> >+ skb->len = skb_orig_len; > > >> >+ } > > >> >+ } > > >> >+ > > >> >+ return proto; > > >> >+} > > >> >+ > > >> > static void prb_del_retire_blk_timer(struct tpacket_kbdq_core *pkc) > > >> > { > > >> > del_timer_sync(&pkc->retire_blk_timer); > > >> >@@ -1007,10 +1062,16 @@ static void prb_clear_rxhash(struct tpacket_kbdq_core *pkc, > > >> > static void prb_fill_vlan_info(struct tpacket_kbdq_core *pkc, > > >> > struct tpacket3_hdr *ppd) > > >> > { > > >> >+ struct packet_sock *po = container_of(pkc, struct packet_sock, rx_ring.prb_bdqc); > > >> >+ > > >> > if (skb_vlan_tag_present(pkc->skb)) { > > >> > ppd->hv1.tp_vlan_tci = skb_vlan_tag_get(pkc->skb); > > >> > ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->vlan_proto); > > >> > ppd->tp_status = TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > > >> >+ } else if (unlikely(po->sk.sk_type == SOCK_DGRAM && eth_type_vlan(pkc->skb->protocol))) { > > >> >+ ppd->hv1.tp_vlan_tci = vlan_get_tci(pkc->skb, pkc->skb->dev); > > >> >+ ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->protocol); > > >> >+ ppd->tp_status = TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > > >> > } else { > > >> > ppd->hv1.tp_vlan_tci = 0; > > >> > ppd->hv1.tp_vlan_tpid = 0; > > >> >@@ -2428,6 +2489,10 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, > > >> > h.h2->tp_vlan_tci = skb_vlan_tag_get(skb); > > >> > h.h2->tp_vlan_tpid = ntohs(skb->vlan_proto); > > >> > status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > > >> >+ } else if (unlikely(sk->sk_type == SOCK_DGRAM && eth_type_vlan(skb->protocol))) { > > >> >+ h.h2->tp_vlan_tci = vlan_get_tci(skb, skb->dev); > > >> >+ h.h2->tp_vlan_tpid = ntohs(skb->protocol); > > >> >+ status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > > >> > } else { > > >> > h.h2->tp_vlan_tci = 0; > > >> > h.h2->tp_vlan_tpid = 0; > > >> >@@ -2457,7 +2522,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, > > >> > sll->sll_halen = dev_parse_header(skb, sll->sll_addr); > > >> > sll->sll_family = AF_PACKET; > > >> > sll->sll_hatype = dev->type; > > >> >- sll->sll_protocol = skb->protocol; > > >> >+ sll->sll_protocol = (sk->sk_type == SOCK_DGRAM) ? > > >> >+ vlan_get_protocol_dgram(skb) : skb->protocol; > > >> > sll->sll_pkttype = skb->pkt_type; > > >> > if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV))) > > >> > sll->sll_ifindex = orig_dev->ifindex; > > >> >@@ -3482,7 +3548,8 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, > > >> > /* Original length was stored in sockaddr_ll fields */ > > >> > origlen = PACKET_SKB_CB(skb)->sa.origlen; > > >> > sll->sll_family = AF_PACKET; > > >> >- sll->sll_protocol = skb->protocol; > > >> >+ sll->sll_protocol = (sock->type == SOCK_DGRAM) ? > > >> >+ vlan_get_protocol_dgram(skb) : skb->protocol; > > >> > } > > >> > > > >> > sock_recv_cmsgs(msg, sk, skb); > > >> >@@ -3539,6 +3606,21 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, > > >> > aux.tp_vlan_tci = skb_vlan_tag_get(skb); > > >> > aux.tp_vlan_tpid = ntohs(skb->vlan_proto); > > >> > aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID; > > >> >+ } else if (unlikely(sock->type == SOCK_DGRAM && eth_type_vlan(skb->protocol))) { > > >> > > >> I don't understand why this would be needed here. We spent quite a bit > > >> of efford in the past to make sure vlan header is always stripped. > > >> Could you fix that in tx path to fulfill the expectation? > > > > > >Doesn't that require NETIF_F_HW_VLAN_CTAG_TX? > > > > > >I also wondered whether we should just convert the skb for this case > > >with skb_vlan_untag, to avoid needing new PF_PACKET logic to handle > > >unstripped tags in the packet socket code. But it seems equally > > >complex. > > > > Correct. skb_vlan_untag() as a preparation of skb before this function > > is called is exactly what I was suggesting. > > It's not necessarily simpler, as that function expects skb->data to > point to the (outer) VLAN header. > > It will pull that one, but not any subsequent ones. > > SOCK_DGRAM expects skb->data to point to the network layer header. > And we only want to make this change for SOCK_DGRAM and if auxdata is > requested. > > Not sure that it will be simpler. But worth a look at least. Thank you for your suggestion. I have analyzed the code and considered a feasible approach. We could call skb_vlan_untag() in packet_rcv before pushing skb into sk->sk_receive_queue. We would also need to determine if auxdata is required to maintain performance, which might cause the logic of judging PACKET_SOCK_AUXDATA to be spread across both the packet_rcv() and packet_recvmsg() functions. The skb_vlan_untag() function handles VLANs in a more comprehensive way, but it seems to have a greater performance impact compared to our current approach. As I am not an expert in this domain, I might have overlooked some important aspects. I would appreciate it if you could share your thoughts on this decision.
