[PATCH] netfilter: fix regression in looped (broad|multi)cast's MAC handing

In 5648b5e1169f, the test for non-empty MAC header introduced in
2c38de4c1f8da7 has been replaced with a test for a set MAC header,
which breaks the case when the MAC header has been reset (using
skb_reset_mac_header), as is the case with looped-back multicast
packets.

This patch adds a test for a non-empty MAC header in addition to the
test for a set MAC header.  The same two tests are also implemented in
nfnetlink_log.c, where the initial code of 2c38de4c1f8da7 has not been
touched, but where supposedly the same situation may happen.

Signed-off-by: Ignacy Gawędzki <redacted>
---
 net/netfilter/nfnetlink_log.c   | 3 ++-
 net/netfilter/nfnetlink_queue.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index 691ef4cffdd9..7f83f9697fc1 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c

@@ -556,7 +556,8 @@ __build_packet_message(struct nfnl_log_net *log,
 		goto nla_put_failure;
 
 	if (indev && skb->dev &&
-	    skb->mac_header != skb->network_header) {
+	    skb_mac_header_was_set(skb) &&
+	    skb_mac_header_len(skb) != 0) {
 		struct nfulnl_msg_packet_hw phw;
 		int len;
 

diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 4acc4b8e9fe5..959527708e38 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c

@@ -560,7 +560,8 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
 		goto nla_put_failure;
 
 	if (indev && entskb->dev &&
-	    skb_mac_header_was_set(entskb)) {
+	    skb_mac_header_was_set(entskb) &&
+	    skb_mac_header_len(entskb) != 0) {
 		struct nfqnl_msg_packet_hw phw;
 		int len;
 

-- 
2.32.0

12/10/21 3:26 PM, Ignacy Gawędzki пишет:

In 5648b5e1169f, the test for non-empty MAC header introduced in
2c38de4c1f8da7 has been replaced with a test for a set MAC header,
which breaks the case when the MAC header has been reset (using
skb_reset_mac_header), as is the case with looped-back multicast
packets.

This patch adds a test for a non-empty MAC header in addition to the
test for a set MAC header.  The same two tests are also implemented in
nfnetlink_log.c, where the initial code of 2c38de4c1f8da7 has not been
touched, but where supposedly the same situation may happen.

Fixes: 2c38de4c1f8da7 ("netfilter: fix looped (broad|multi)cast's MAC handling")