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Date: Mon, 17 Jun 2024 13:27:04 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Chengen Du <chengen.du@...onical.com>
Cc: willemdebruijn.kernel@...il.com, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
kaber@...sh.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v8] af_packet: Handle outgoing VLAN packets without
hardware offloading
Mon, Jun 17, 2024 at 07:45:14AM CEST, chengen.du@...onical.com 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@canonical.com/T/#u
>Fixes: 393e52e33c6c ("packet: deliver VLAN TCI to userspace")
>Cc: stable@...r.kernel.org
>Signed-off-by: Chengen Du <chengen.du@...onical.com>
>---
> 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?
>+ struct sockaddr_ll *sll = &PACKET_SKB_CB(skb)->sa.ll;
>+ struct net_device *dev;
>+
>+ rcu_read_lock();
>+ dev = dev_get_by_index_rcu(sock_net(sk), sll->sll_ifindex);
>+ if (dev) {
>+ aux.tp_vlan_tci = vlan_get_tci(skb, dev);
>+ aux.tp_vlan_tpid = ntohs(skb->protocol);
>+ aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
>+ } else {
>+ aux.tp_vlan_tci = 0;
>+ aux.tp_vlan_tpid = 0;
>+ }
>+ rcu_read_unlock();
> } else {
> aux.tp_vlan_tci = 0;
> aux.tp_vlan_tpid = 0;
>--
>2.43.0
>
>
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