xdpgeneric, XDP_PASS, and bpf_xdp_adjust_head decapsulation dropping packets

I am having an issue with xdpgeneric specifically when using XDP_PASS after bpf_xdp_adjust_head to pop some headers off. My test environment is qemu using virtio_net specifically, but it also happens with e1000 in qemu/physical devices.

On a real NIC (ixgbe), the same program is successfully passing decapsulated traffic, but fails in the same way when forcing xdpgeneric mode.

Here is the packet outside of my VM, with the IP+UDP+tun header.

# sudo tcpdump -ni ens5-outside -e udp -vvvXc1
tcpdump: listening on ens5-outside, link-type EN10MB (Ethernet), capture size 262144 bytes
15:54:14.263306 06:54:00:00:00:01 > 06:54:01:00:00:01, ethertype IPv4 (0x0800), length 127: (tos 0x0, ttl 255, id 0, offset 0, flags [DF], proto UDP (17), length 113)
    172.64.0.108.39999 > 172.64.0.101.7803: [no cksum] UDP, length 85
	0x0000:  4500 0071 0000 4000 ff11 222a ac40 006c  E..q..@..."*[email protected]
	0x0010:  ac40 0065 9c3f 1e7b 005d 0000 0145 0000  [email protected].?.{.]...E..
	0x0020:  54e3 6b40 003f 01d5 e8c0 a800 02c0 a801  T.k@.?..........
	0x0030:  0208 002c b1b0 5eb8 f196 ca40 5d00 0000  ...,..^....@]...
	0x0040:  00c8 0304 0000 0000 0010 1112 1314 1516  ................
	0x0050:  1718 191a 1b1c 1d1e 1f20 2122 2324 2526  ..........!"#$%&
	0x0060:  2728 292a 2b2c 2d2e 2f30 3132 3334 3536  '()*+,-./0123456
	0x0070:  37                                       7

My XDP program copies the original ethhdr to the new offset and adjusts the head forward, and I can see the resulting ICMP packet is valid with tcpdump inside the VM:

# tcpdump -niens5 icmp -c1 -vXe
tcpdump: listening on ens5, link-type EN10MB (Ethernet), capture size 262144 bytes
15:53:25.602109 06:54:00:00:00:01 > 06:54:01:00:00:01, ethertype IPv4 (0x0800), length 98: (tos 0x0, ttl 63, id 35986, offset 0, flags [DF], proto ICMP (1), length 84)
    192.168.0.2 > 192.168.1.2: ICMP echo request, id 45150, seq 43683, length 64
	0x0000:  4500 0054 8c92 4000 3f01 2cc2 c0a8 0002  E..T..@.?.,.....
	0x0010:  c0a8 0102 0800 ed79 b05e aaa3 6dca 405d  .......y.^..m.@]
	0x0020:  0000 0000 3589 0d00 0000 0000 1011 1213  ....5...........
	0x0030:  1415 1617 1819 1a1b 1c1d 1e1f 2021 2223  .............!"#
	0x0040:  2425 2627 2829 2a2b 2c2d 2e2f 3031 3233  $%&'()*+,-./0123
	0x0050:  3435 3637                                4567

Unfortunately, at this point, the packet is dropped in ip_rcv_core. I added a perf probe on the specific drop line that I'm hitting, and printing the skb->len and len (from ntohs(iph->tot_len)) variables. You can see the obviously wrong len value below, while a packet capture in the VM does show the correct value for tot_len in the IP header.

# perf probe -L ip_rcv_core:64+4 | cat
<ip_rcv_core@/usr/src/debug/kernel-debug-5.2.2-1.2.x86_64/linux-5.2/linux-obj/../net/ipv4/ip_input.c:64>
     64  	if (pskb_trim_rcsum(skb, len)) {
     65  		__IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
     66  		goto drop;
         	}

# perf probe -a 'ip_rcv_core:66 skb=skb->len:u32 len=len:u32'
	swapper     0 [001] 84794.954487: probe:ip_rcv_core: (ffffffffbcbd5a7d) skb=84 len=4294931717
	swapper     0 [001] 84794.965473: probe:ip_rcv_core: (ffffffffbcbd5a7d) skb=84 len=4294936833

In contrast, here's what it looks like in XDP native mode (different line number but looking):

# perf probe -a 'ip_rcv_core:57 skb=skb->len:u32 len=len:u32'
	swapper     0 [000]   353.187439: probe:ip_rcv_core: (ffffffffac9dcca7) skb=84 len=84
	swapper     0 [003]   353.187577: probe:ip_rcv_core: (ffffffffac9dcca7) skb=84 len=84

Here's the relevant portion of my program where I decapsulate:

static __always_inline int handle_peer_data_ipv4(struct xdp_md *ctx)

{
	void *data, *data_end;
	struct ethhdr *eth, *orig_eth;
	__u32 csum = 0;

	data = (void *)(unsigned long)ctx->data;
	data_end = (void *)(unsigned long)ctx->data_end;

	if (data + sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct tunnel_header) > data_end) {
		return XDP_DROP;
	}

	orig_eth = data;
	eth = data + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct tunnel_header);
	memcpy(&eth->h_source, &orig_eth->h_source, ETH_ALEN);
	memcpy(&eth->h_dest, &orig_eth->h_dest, ETH_ALEN);
	eth->h_proto = __constant_htons(ETH_P_IP);

	/* Decapsulate by removing IP + UDP + tunnel headers */
	if (bpf_xdp_adjust_head(ctx, (int)(sizeof(struct iphdr) + sizeof(struct udphdr) +
					   sizeof(struct tunnel_header)))) {
		return XDP_DROP;
	}

	return XDP_PASS;
}

struct tunnel_header {
	__u8 flags;
};

Kernel is 5.2.2-1-debug, OS is openSUSE Tumbleweed 20190724. For qemu I run with these arguments for the NICs:

# qemu (...) -netdev tap,br=vm-bridge,id=hostnet1,ifname=ens5-outside,queues=4,vhost=on \
-device virtio-net-pci,mq=on,vectors=9,guest_tso4=off,guest_tso6=off,netdev=hostnet1,id=net1,mac=06:54:01:00:00:01

First of all, thank you for this VERY excellent bug-report! My comments inlined below.

Cc. Stephen as this might be related to:
commit 458bf2f224f0 ("net: core: support XDP generic on stacked devices.") (Author: Stephen Hemminger).

Are you sure you are using "xdpgeneric" mode?
As virtio_net do have "native" XDP mode.

                      ^^^^

iph->tot_len

$ echo $((0x71))
113

$ echo $((0x71+14))
127

                                                 ^^ ^^

Encapsulated packet starts at a funny offset, making it harder to follow.

^^ ^^
Encapsulated iph->tot_len and ipproto=ICMP

^^ ^^
iph->tot_len and ipproto=ICMP

$ echo $((0x54))
84

$ echo $((0x54+14))
98

The len from ntohs(iph->tot_len) is obviously wrong (len=4294931717), but given it comes the packet data, it can easily be a mistake in your adjustment of headers. But from above packet dump, the iph->tot_len is correct. Thus, this indicate that how we find the IP-header offset is likely broken...

Looking at the code, I think the packet will be dropped earlier than the pskb_trim_rcsum() call, in the check if (skb->len < len).

	iph = ip_hdr(skb);
	[...]

	len = ntohs(iph->tot_len);
	if (skb->len < len) {
		__IP_INC_STATS(net, IPSTATS_MIB_INTRUNCATEDPKTS);
		goto drop;
	} else if (len < (iph->ihl*4))
		goto inhdr_error;

	/* Our transport medium may have padded the buffer out. Now we know it
	 * is IP we can trim to the true length of the frame.
	 * Note this now means skb->len holds ntohs(iph->tot_len).
	 */
	if (pskb_trim_rcsum(skb, len)) {
		__IP_INC_STATS(net, IPSTATS_MIB_INDISCARDS);
		goto drop;
	}

The bug might hide in iph=ip_hdr(skb) which is found via skb->network_header (via helper ip_hdr => skb_network_header(skb)).

You only support IPv4 encapsulated packets?

Do you handle ARP requests separately?

Can you test an earlier kernel, specifically before: commit 458bf2f224f0 ("net: core: support XDP generic on stacked devices.") (Author: Stephen Hemminger)

$ git describe --contains  458bf2f224f04
v5.2-rc3~26^2~11^2

I fear that this commit, which moved generic-XDP to a later call point, might cause this. Because it could be that the SKB network_header update, is now done before calling XDP program (... still looking at code details).

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

On Thu, 1 Aug 2019 10:18:49 +0200
Jesper Dangaard Brouer <[email protected]> wrote:

[...]

[...]

I now have a reproducer myself, and I can confirm that this commit 458bf2f224f0 ("net: core: support XDP generic on stacked devices.") is the issue... reverting it fixes the problem. (I don't have a fix yet)

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

I do have a fix now... It was a matter of calling skb_reset_network_header() which will fix the issue with ip_hdr(skb) as I suspect was wrong (as explained earlier).

I wonder if we also need to call skb_reset_transport_header(skb) ?

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Thank you very much for your prompt and detailed review of my report! Some of these answers may be moot now that you have found the specific commit that caused the issue.

The program is loaded with XDP_FLAGS_SKB_MODE in this case. I'm having a separate issue with "native" XDP on virtio_net that I'm working on but it is more likely an issue with my code.

Sorry about that. I should have made it easier.

I had the same suspicion but a probe in the corresponding drop showed no results, and furthermore, the InTruncatedPkts SNMP counter was not increasing.

Sorry, I wanted a minimal example so this is stripped down.

You have already confirmed this but I can also confirm that a kernel before commit 458bf2f224f0 works with no changes to my program.

True.

No problem.

Strange.

I figured, that you already handled that.

Thanks for also confirming. I've just send a patchset with fixes:
https://patchwork.ozlabs.org/project/netdev/list/?series=122796&state=%2a

I can recommend that you look at the selftest script test_xdp_vlan.sh:
https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/test_xdp_vlan.sh

Which uses veth and network namespaces for testing. If you get the hint, then you can actually create these small scripts, that can function as unit and regression tests for XDP code snippets.

Our XDP-tutorial also uses veth as a development environment:
https://github.com/xdp-project/xdp-tutorial/tree/master/testenv

Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

[...]

Thank you for this; I tested this against my environment and it works as expected again.

Great hint, I will definitely use these going forward!

Thanks to Brandon Cazander, who wrote a very detailed bug report that even used perf probe's on xdp-newbies mailing list, we discovered that generic-XDP contains some regressions when using bpf_xdp_adjust_head().

First issue were that my selftests script, that use bpf_xdp_adjust_head(), by mistake didn't use generic-XDP any-longer. That selftest should have caught the real regression introduced in commit 458bf2f224f0 ("net: core:
support XDP generic on stacked devices.").

To verify this patchset fix the regressions, you can invoked manually via:

cd tools/testing/selftests/bpf/
sudo ./test_xdp_vlan_mode_generic.sh
sudo ./test_xdp_vlan_mode_native.sh

Reported by: Brandon Cazander <[email protected]>

---

Jesper Dangaard Brouer (4):
bpf: fix XDP vlan selftests test_xdp_vlan.sh selftests/bpf: add wrapper scripts for test_xdp_vlan.sh selftests/bpf: reduce time to execute test_xdp_vlan.sh
net: fix bpf_xdp_adjust_head regression for generic-XDP

 net/core/dev.c                                     |   15 ++++-
 tools/testing/selftests/bpf/Makefile               |    3 +
 tools/testing/selftests/bpf/test_xdp_vlan.sh       |   57 ++++++++++++++++----
 .../selftests/bpf/test_xdp_vlan_mode_generic.sh    |    9 +++
 .../selftests/bpf/test_xdp_vlan_mode_native.sh     |    9 +++
 5 files changed, 75 insertions(+), 18 deletions(-)
 create mode 100755 tools/testing/selftests/bpf/test_xdp_vlan_mode_generic.sh
 create mode 100755 tools/testing/selftests/bpf/test_xdp_vlan_mode_native.sh

--

Change BPF selftest test_xdp_vlan.sh to (default) use generic XDP.

This selftest was created together with a fix for generic XDP, in commit 297249569932 ("net: fix generic XDP to handle if eth header was mangled"). And was suppose to catch if generic XDP was broken again.

The tests are using veth and assumed that veth driver didn't support native driver XDP, thus it used the (ip link set) 'xdp' attach that fell back to generic-XDP. But veth gained native-XDP support in 948d4f214fde ("veth: Add driver XDP"), which caused this test script to use native-XDP.

---
 tools/testing/selftests/bpf/test_xdp_vlan.sh |   42 ++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 6 deletions(-)

index 51a3a31d1aac..c8aed63b0ffe 100755
@@ -1,7 +1,12 @@
 #!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Author: Jesper Dangaard Brouer <[email protected]>
 
 TESTNAME=xdp_vlan
 
+# Default XDP mode
+XDP_MODE=xdpgeneric
+
 usage() {
   echo "Testing XDP + TC eBPF VLAN manipulations: $TESTNAME"
   echo ""

@@ -9,9 +14,23 @@ usage() {
   echo "  -v | --verbose : Verbose"
   echo "  --flush        : Flush before starting (e.g. after --interactive)"
   echo "  --interactive  : Keep netns setup running after test-run"
+  echo "  --mode=XXX     : Choose XDP mode (xdp | xdpgeneric | xdpdrv)"
   echo ""
 }
 
+valid_xdp_mode()
+{
+	local mode=$1
+
+	case "$mode" in
+		xdpgeneric | xdpdrv | xdp)
+			return 0
+			;;
+		*)
+			return 1
+	esac
+}
+
 cleanup()
 {
 	local status=$?

@@ -37,7 +56,7 @@ cleanup()
 
 # Using external program "getopt" to get --long-options
 OPTIONS=$(getopt -o hvfi: \
-    --long verbose,flush,help,interactive,debug -- "$@")
+    --long verbose,flush,help,interactive,debug,mode: -- "$@")
 if (( $? != 0 )); then
     usage
     echo "selftests: $TESTNAME [FAILED] Error calling getopt, unknown option?"

@@ -60,6 +79,11 @@ while true; do
 		cleanup
 		shift
 		;;
+	    --mode )
+		shift
+		XDP_MODE=$1
+		shift
+		;;
 	    -- )
 		shift
 		break

@@ -81,8 +105,14 @@ if [ "$EUID" -ne 0 ]; then
 	exit 1
 fi
 
-ip link set dev lo xdp off 2>/dev/null > /dev/null
-if [ $? -ne 0 ];then
+valid_xdp_mode $XDP_MODE
+if [ $? -ne 0 ]; then
+	echo "selftests: $TESTNAME [FAILED] unknown XDP mode ($XDP_MODE)"
+	exit 1
+fi
+
+ip link set dev lo xdpgeneric off 2>/dev/null > /dev/null
+if [ $? -ne 0 ]; then
 	echo "selftests: $TESTNAME [SKIP] need ip xdp support"
 	exit 0
 fi

@@ -166,7 +196,7 @@ export FILE=test_xdp_vlan.o
 
 # First test: Remove VLAN by setting VLAN ID 0, using "xdp_vlan_change"
 export XDP_PROG=xdp_vlan_change
-ip netns exec ns1 ip link set $DEVNS1 xdp object $FILE section $XDP_PROG
+ip netns exec ns1 ip link set $DEVNS1 $XDP_MODE object $FILE section $XDP_PROG
 
 # In ns1: egress use TC to add back VLAN tag 4011
 #  (del cmd)

@@ -187,8 +217,8 @@ ip netns exec ns1 ping -W 2 -c 3 $IPADDR2
 # ETH_P_8021Q indication, and this cause overwriting of our changes.
 #
 export XDP_PROG=xdp_vlan_remove_outer2
-ip netns exec ns1 ip link set $DEVNS1 xdp off
-ip netns exec ns1 ip link set $DEVNS1 xdp object $FILE section $XDP_PROG
+ip netns exec ns1 ip link set $DEVNS1 $XDP_MODE off
+ip netns exec ns1 ip link set $DEVNS1 $XDP_MODE object $FILE section $XDP_PROG
 
 # Now the namespaces should still be able reach each-other, test with ping:
 ip netns exec ns2 ping -W 2 -c 3 $IPADDR1

In-order to test both native-XDP (xdpdrv) and generic-XDP (xdpgeneric) create two wrapper test scripts, that start the test_xdp_vlan.sh script with these modes.

---
 tools/testing/selftests/bpf/Makefile               |    3 ++-
 tools/testing/selftests/bpf/test_xdp_vlan.sh       |    5 ++++-
 .../selftests/bpf/test_xdp_vlan_mode_generic.sh    |    9 +++++++++
 .../selftests/bpf/test_xdp_vlan_mode_native.sh     |    9 +++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/bpf/test_xdp_vlan_mode_generic.sh
 create mode 100755 tools/testing/selftests/bpf/test_xdp_vlan_mode_native.sh

index 3bd0f4a0336a..29001f944db7 100644
@@ -57,7 +57,8 @@ TEST_PROGS := test_kmod.sh \
 	test_lirc_mode2.sh \
 	test_skb_cgroup_id.sh \
 	test_flow_dissector.sh \
-	test_xdp_vlan.sh \
+	test_xdp_vlan_mode_generic.sh \
+	test_xdp_vlan_mode_native.sh \
 	test_lwt_ip_encap.sh \
 	test_tcp_check_syncookie.sh \
 	test_tc_tunnel.sh \

index c8aed63b0ffe..7348661be815 100755
@@ -2,7 +2,10 @@
 # SPDX-License-Identifier: GPL-2.0
 # Author: Jesper Dangaard Brouer <[email protected]>
 
-TESTNAME=xdp_vlan
+# Allow wrapper scripts to name test
+if [ -z "$TESTNAME" ]; then
+    TESTNAME=xdp_vlan
+fi
 
 # Default XDP mode
 XDP_MODE=xdpgeneric

new file mode 100755
index 000000000000..c515326d6d59
@@ -0,0 +1,9 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Exit on failure
+set -e
+
+# Wrapper script to test generic-XDP
+export TESTNAME=xdp_vlan_mode_generic
+./test_xdp_vlan.sh --mode=xdpgeneric

new file mode 100755
index 000000000000..5cf7ce1f16c1
@@ -0,0 +1,9 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Exit on failure
+set -e
+
+# Wrapper script to test native-XDP
+export TESTNAME=xdp_vlan_mode_native
+./test_xdp_vlan.sh --mode=xdpdrv

Given the increasing number of BPF selftests, it makes sense to reduce the time to execute these tests. The ping parameters are adjusted to reduce the time from measures 9 sec to approx 2.8 sec.

---
 tools/testing/selftests/bpf/test_xdp_vlan.sh |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

index 7348661be815..bb8b0da91686 100755
@@ -188,7 +188,7 @@ ip netns exec ns2 ip link set lo up
 # At this point, the hosts cannot reach each-other,
 # because ns2 are using VLAN tags on the packets.
 
-ip netns exec ns2 sh -c 'ping -W 1 -c 1 100.64.41.1 || echo "Okay ping fails"'
+ip netns exec ns2 sh -c 'ping -W 1 -c 1 100.64.41.1 || echo "Success: First ping must fail"'
 
 
 # Now we can use the test_xdp_vlan.c program to pop/push these VLAN tags

@@ -210,8 +210,8 @@ ip netns exec ns1 tc filter add dev $DEVNS1 egress \
   prio 1 handle 1 bpf da obj $FILE sec tc_vlan_push
 
 # Now the namespaces can reach each-other, test with ping:
-ip netns exec ns2 ping -W 2 -c 3 $IPADDR1
-ip netns exec ns1 ping -W 2 -c 3 $IPADDR2
+ip netns exec ns2 ping -i 0.2 -W 2 -c 2 $IPADDR1
+ip netns exec ns1 ping -i 0.2 -W 2 -c 2 $IPADDR2
 
 # Second test: Replace xdp prog, that fully remove vlan header
 #

@@ -224,5 +224,5 @@ ip netns exec ns1 ip link set $DEVNS1 $XDP_MODE off
 ip netns exec ns1 ip link set $DEVNS1 $XDP_MODE object $FILE section $XDP_PROG
 
 # Now the namespaces should still be able reach each-other, test with ping:
-ip netns exec ns2 ping -W 2 -c 3 $IPADDR1
-ip netns exec ns1 ping -W 2 -c 3 $IPADDR2
+ip netns exec ns2 ping -i 0.2 -W 2 -c 2 $IPADDR1
+ip netns exec ns1 ping -i 0.2 -W 2 -c 2 $IPADDR2

When generic-XDP was moved to a later processing step by commit 458bf2f224f0 ("net: core: support XDP generic on stacked devices.") a regression was introduced when using bpf_xdp_adjust_head.

The issue is that after this commit the skb->network_header is now changed prior to calling generic XDP and not after. Thus, if the header is changed by XDP (via bpf_xdp_adjust_head), then skb->network_header also need to be updated again. Fix by calling skb_reset_network_header().

---
 net/core/dev.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

index fc676b2610e3..b5533795c3c1 100644
@@ -4374,12 +4374,17 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 
 	act = bpf_prog_run_xdp(xdp_prog, xdp);
 
+	/* check if bpf_xdp_adjust_head was used */
 	off = xdp->data - orig_data;
-	if (off > 0)
-		__skb_pull(skb, off);
-	else if (off < 0)
-		__skb_push(skb, -off);
-	skb->mac_header += off;
+	if (off) {
+		if (off > 0)
+			__skb_pull(skb, off);
+		else if (off < 0)
+			__skb_push(skb, -off);
+
+		skb->mac_header += off;
+		skb_reset_network_header(skb);
+	}
 
 	/* check if bpf_xdp_adjust_tail was used. it can only "shrink"
 	 * pckt.

Out of curiosity what was your conclusion regarding resetting the transport header as well?

Well, I don't know... I need some review, from e.g. Stephen that changed this... I've added code snippets below signature to helper reviewers (also helps understand below paragraph).

I think, we perhaps should call skb_reset_transport_header(), as we change skb->data (via either __skb_pull() or __skb_push()), *BUT* I'm not sure it is needed/required, as someone/something afterwards still need to call skb_set_transport_header(), which also calls skb_reset_transport_header() anyway.

I also want to ask reviewers, if we should move the call to skb_reset_mac_len() (which Stephen added) in __netif_receive_skb_core() into netif_receive_generic_xdp() (after the call to skb_reset_network_header()), (it would be more natural to keep them together)?

- -
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer

Code snippet

	/* check if bpf_xdp_adjust_head was used */
	off = xdp->data - orig_data;
	if (off) {
		if (off > 0)
			__skb_pull(skb, off);
		else if (off < 0)
			__skb_push(skb, -off);

		skb->mac_header += off;
		skb_reset_network_header(skb);
	}

static inline bool skb_transport_header_was_set(const struct sk_buff *skb)

{
	return skb->transport_header != (typeof(skb->transport_header))~0U;
}

static inline unsigned char *skb_transport_header(const struct sk_buff *skb)

{
	return skb->head + skb->transport_header;
}

static inline void skb_reset_transport_header(struct sk_buff *skb)

{
	skb->transport_header = skb->data - skb->head;
}

static inline void skb_set_transport_header(struct sk_buff *skb,
const int offset)

{
	skb_reset_transport_header(skb);
	skb->transport_header += offset;
}

Perhaps you've seen this, but just in case - this is the last commit that touched the transport header setting in __netif_receive_skb(), and it sounds like it matters mostly for qdisc accounting?

commit fda55eca5a33f33ffcd4192c6b2d75179714a52c

Author: Eric Dumazet <[email protected]>
Date:   Mon Jan 7 09:28:21 2013 +0000

net: introduce skb_transport_header_was_set()

We have skb_mac_header_was_set() helper to tell if mac_header was set on a skb. We would like the same for transport_header.

__netif_receive_skb() doesn't reset the transport header if already set by GRO layer.

Note that network stacks usually reset the transport header anyway, after pulling the network header, so this change only allows a followup patch to have more precise qdisc pkt_len computation for GSO packets at ingress side.

From: Jesper Dangaard Brouer <[email protected]>
Date: Thu, 01 Aug 2019 20:00:11 +0200

Series applied and queued up for -stable, thanks.