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. > >Aside from this conversation whether we need to support this >unstripped case at all, code LGTM.
