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.
