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[34.86.148.56]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6b5033f8a0esm17154246d6.134.2024.06.20.00.36.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jun 2024 00:36:47 -0700 (PDT) Date: Thu, 20 Jun 2024 03:36:46 -0400 From: Willem de Bruijn To: Chengen Du , Willem de Bruijn Cc: Jiri Pirko , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, kaber@trash.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Message-ID: <6673dc0ee45dd_2a03042941e@willemb.c.googlers.com.notmuch> In-Reply-To: References: <20240617054514.127961-1-chengen.du@canonical.com> <6670898e1ca78_21d16f2946f@willemb.c.googlers.com.notmuch> <66715247c147c_23a4e7294a7@willemb.c.googlers.com.notmuch> Subject: Re: [PATCH v8] af_packet: Handle outgoing VLAN packets without hardware offloading Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Chengen Du wrote: > On Tue, Jun 18, 2024 at 5:24=E2=80=AFPM Willem de Bruijn > wrote: > > > > Jiri Pirko wrote: > > > Mon, Jun 17, 2024 at 09:07:58PM CEST, willemdebruijn.kernel@gmail.c= om wrote: > > > >Jiri Pirko wrote: > > > >> Mon, Jun 17, 2024 at 07:45:14AM CEST, chengen.du@canonical.com w= rote: > > > >> >The issue initially stems from libpcap. The ethertype will be o= verwritten > > > >> >as the VLAN TPID if the network interface lacks hardware VLAN o= ffloading. > > > >> >In the outbound packet path, if hardware VLAN offloading is una= vailable, > > > >> >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 ch= ecking 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() functi= on 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 determin= ing the > > > >> >correct TCI-TPID value. Additionally, the protocol in SLL is in= correct, > > > >> >which means the packet capturing tool cannot parse the L3 heade= r correctly. > > > >> > > > > >> >Link: https://github.com/the-tcpdump-group/libpcap/issues/1105 > > > >> >Link: https://lore.kernel.org/netdev/20240520070348.26725-1-che= ngen.du@canonical.com/T/#u > > > >> >Fixes: 393e52e33c6c ("packet: deliver VLAN TCI to userspace") > > > >> >Cc: stable@vger.kernel.org > > > >> >Signed-off-by: Chengen Du > > > >> >--- > > > >> > 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 p= acket_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 =3D skb->data; > > > >> >+ int skb_orig_len =3D 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 =3D=3D dev->hard_header_len) > > > >> >+ header_len =3D dev->hard_header_len; > > > >> >+ else if (is_vlan_dev(dev)) > > > >> >+ header_len =3D dev->min_header_len; > > > >> >+ else > > > >> >+ return 0; > > > >> >+ > > > >> >+ skb_push(skb, skb->data - skb_mac_header(skb)); > > > >> >+ vh =3D skb_header_pointer(skb, header_len, sizeof(vhdr), &vhd= r); > > > >> >+ if (skb_orig_data !=3D skb->data) { > > > >> >+ skb->data =3D skb_orig_data; > > > >> >+ skb->len =3D 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 =3D skb->protocol; > > > >> >+ > > > >> >+ if (unlikely(eth_type_vlan(proto))) { > > > >> >+ u8 *skb_orig_data =3D skb->data; > > > >> >+ int skb_orig_len =3D skb->len; > > > >> >+ > > > >> >+ skb_push(skb, skb->data - skb_mac_header(skb)); > > > >> >+ proto =3D __vlan_get_protocol(skb, proto, NULL); > > > >> >+ if (skb_orig_data !=3D skb->data) { > > > >> >+ skb->data =3D skb_orig_data; > > > >> >+ skb->len =3D 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 tpa= cket_kbdq_core *pkc, > > > >> > static void prb_fill_vlan_info(struct tpacket_kbdq_core *pkc, > > > >> > struct tpacket3_hdr *ppd) > > > >> > { > > > >> >+ struct packet_sock *po =3D container_of(pkc, struct packet_so= ck, rx_ring.prb_bdqc); > > > >> >+ > > > >> > if (skb_vlan_tag_present(pkc->skb)) { > > > >> > ppd->hv1.tp_vlan_tci =3D skb_vlan_tag_get(pkc->skb); > > > >> > ppd->hv1.tp_vlan_tpid =3D ntohs(pkc->skb->vlan_proto)= ; > > > >> > ppd->tp_status =3D TP_STATUS_VLAN_VALID | TP_STATUS_V= LAN_TPID_VALID; > > > >> >+ } else if (unlikely(po->sk.sk_type =3D=3D SOCK_DGRAM && eth_t= ype_vlan(pkc->skb->protocol))) { > > > >> >+ ppd->hv1.tp_vlan_tci =3D vlan_get_tci(pkc->skb, pkc->= skb->dev); > > > >> >+ ppd->hv1.tp_vlan_tpid =3D ntohs(pkc->skb->protocol); > > > >> >+ ppd->tp_status =3D TP_STATUS_VLAN_VALID | TP_STATUS_V= LAN_TPID_VALID; > > > >> > } else { > > > >> > ppd->hv1.tp_vlan_tci =3D 0; > > > >> > ppd->hv1.tp_vlan_tpid =3D 0; > > > >> >@@ -2428,6 +2489,10 @@ static int tpacket_rcv(struct sk_buff *s= kb, struct net_device *dev, > > > >> > h.h2->tp_vlan_tci =3D skb_vlan_tag_get(skb); > > > >> > h.h2->tp_vlan_tpid =3D ntohs(skb->vlan_proto)= ; > > > >> > status |=3D TP_STATUS_VLAN_VALID | TP_STATUS_= VLAN_TPID_VALID; > > > >> >+ } else if (unlikely(sk->sk_type =3D=3D SOCK_DGRAM && = eth_type_vlan(skb->protocol))) { > > > >> >+ h.h2->tp_vlan_tci =3D vlan_get_tci(skb, skb->= dev); > > > >> >+ h.h2->tp_vlan_tpid =3D ntohs(skb->protocol); > > > >> >+ status |=3D TP_STATUS_VLAN_VALID | TP_STATUS_= VLAN_TPID_VALID; > > > >> > } else { > > > >> > h.h2->tp_vlan_tci =3D 0; > > > >> > h.h2->tp_vlan_tpid =3D 0; > > > >> >@@ -2457,7 +2522,8 @@ static int tpacket_rcv(struct sk_buff *sk= b, struct net_device *dev, > > > >> > sll->sll_halen =3D dev_parse_header(skb, sll->sll_addr); > > > >> > sll->sll_family =3D AF_PACKET; > > > >> > sll->sll_hatype =3D dev->type; > > > >> >- sll->sll_protocol =3D skb->protocol; > > > >> >+ sll->sll_protocol =3D (sk->sk_type =3D=3D SOCK_DGRAM) ? > > > >> >+ vlan_get_protocol_dgram(skb) : skb->protocol; > > > >> > sll->sll_pkttype =3D skb->pkt_type; > > > >> > if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV))) > > > >> > sll->sll_ifindex =3D 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 =3D PACKET_SKB_CB(skb)->sa.origlen; > > > >> > sll->sll_family =3D AF_PACKET; > > > >> >- sll->sll_protocol =3D skb->protocol; > > > >> >+ sll->sll_protocol =3D (sock->type =3D=3D 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 =3D skb_vlan_tag_get(skb); > > > >> > aux.tp_vlan_tpid =3D ntohs(skb->vlan_proto); > > > >> > aux.tp_status |=3D TP_STATUS_VLAN_VALID | TP_= STATUS_VLAN_TPID_VALID; > > > >> >+ } else if (unlikely(sock->type =3D=3D SOCK_DGRAM && e= th_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 strippe= d. > > > >> 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 ca= se > > > >with skb_vlan_untag, to avoid needing new PF_PACKET logic to handl= e > > > >unstripped tags in the packet socket code. But it seems equally > > > >complex. > > > > > > Correct. skb_vlan_untag() as a preparation of skb before this funct= ion > > > 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. = Only for SOCK_DGRAM. And there is some user risk, as they will see different packets on the same devices as before. A robust program should work for both vlan stripped and unstripped, and the unstripped case is already broken wrt sll_protocol returned, so I suppose this is acceptable. > 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. You mean to only make the above change if SOCK_DGRAM and auxdata is requested? Btw, also tpacket_rcv, where auxdata is always returned. = > 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. I was afraid of that too. The skb_share_check is fine, as this also exists in packet_rcv, before we would call skb_vlan_untag. A bigger issue: this only pulls the outer tag. So we still need to handle the vlan stacking case correctly manually. > 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.