From 0bcf2e4aca6c29a07555b713f2fb461dc38d5977 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Fri, 21 Apr 2023 01:56:01 +0300 Subject: net: dsa: tag_ocelot: call only the relevant portion of __skb_vlan_pop() on TX ocelot_xmit_get_vlan_info() calls __skb_vlan_pop() as the most appropriate helper I could find which strips away a VLAN header. That's all I need it to do, but __skb_vlan_pop() has more logic, which will become incompatible with the future revert of commit 6d1ccff62780 ("net: reset mac header in dev_start_xmit()"). Namely, it performs a sanity check on skb_mac_header(), which will stop being set after the above revert, so it will return an error instead of removing the VLAN tag. ocelot_xmit_get_vlan_info() gets called in 2 circumstances: (1) the port is under a VLAN-aware bridge and the bridge sends VLAN-tagged packets (2) the port is under a VLAN-aware bridge and somebody else (an 8021q upper) sends VLAN-tagged packets (using a VID that isn't in the bridge vlan tables) In case (1), there is actually no bug to defend against, because br_dev_xmit() calls skb_reset_mac_header() and things continue to work. However, in case (2), illustrated using the commands below, it can be seen that our intervention is needed, since __skb_vlan_pop() complains: $ ip link add br0 type bridge vlan_filtering 1 && ip link set br0 up $ ip link set $eth master br0 && ip link set $eth up $ ip link add link $eth name $eth.100 type vlan id 100 && ip link set $eth.100 up $ ip addr add 192.168.100.1/24 dev $eth.100 I could fend off the checks in __skb_vlan_pop() with some skb_mac_header_was_set() calls, but seeing how few callers of __skb_vlan_pop() there are from TX paths, that seems rather unproductive. As an alternative solution, extract the bare minimum logic to strip a VLAN header, and move it to a new helper named vlan_remove_tag(), close to the definition of vlan_insert_tag(). Document it appropriately and make ocelot_xmit_get_vlan_info() call this smaller helper instead. Seeing that it doesn't appear illegal to test skb->protocol in the TX path, I guess it would be a good for vlan_remove_tag() to also absorb the vlan_set_encap_proto() function call. Signed-off-by: Vladimir Oltean Reviewed-by: Simon Horman Reviewed-by: Florian Fainelli Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller --- include/linux/if_vlan.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'include') diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h index 3698f2b391cd..0f40f379d75c 100644 --- a/include/linux/if_vlan.h +++ b/include/linux/if_vlan.h @@ -685,6 +685,27 @@ static inline void vlan_set_encap_proto(struct sk_buff *skb, skb->protocol = htons(ETH_P_802_2); } +/** + * vlan_remove_tag - remove outer VLAN tag from payload + * @skb: skbuff to remove tag from + * @vlan_tci: buffer to store value + * + * Expects the skb to contain a VLAN tag in the payload, and to have skb->data + * pointing at the MAC header. + * + * Returns a new pointer to skb->data, or NULL on failure to pull. + */ +static inline void *vlan_remove_tag(struct sk_buff *skb, u16 *vlan_tci) +{ + struct vlan_hdr *vhdr = (struct vlan_hdr *)(skb->data + ETH_HLEN); + + *vlan_tci = ntohs(vhdr->h_vlan_TCI); + + memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN); + vlan_set_encap_proto(skb, vhdr); + return __skb_pull(skb, VLAN_HLEN); +} + /** * skb_vlan_tagged - check if skb is vlan tagged. * @skb: skbuff to query -- cgit v1.2.3-70-g09d2