| Message ID | 20230322233823.1806736-10-vladimir.oltean@nxp.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Remove skb_mac_header() dependency in DSA xmit path | expand |
On Thu, Mar 23, 2023 at 01:38:23AM +0200, Vladimir Oltean wrote: > 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 > $ # needed to work around an apparent DSA RX filtering bug > $ ip link set $eth promisc on > > 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 <vladimir.oltean@nxp.com> Reviewed-by: Simon Horman <simon.horman@corigine.com>
On 3/22/23 16:38, Vladimir Oltean wrote: > 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 > $ # needed to work around an apparent DSA RX filtering bug > $ ip link set $eth promisc on > > 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 <vladimir.oltean@nxp.com> Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h index 3698f2b391cd..4d54814143a8 100644 --- a/include/linux/if_vlan.h +++ b/include/linux/if_vlan.h @@ -685,6 +685,26 @@ 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 + * + * 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 diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 050a875d09c5..0a7c058d4849 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5939,7 +5939,6 @@ EXPORT_SYMBOL(skb_ensure_writable); */ int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci) { - struct vlan_hdr *vhdr; int offset = skb->data - skb_mac_header(skb); int err; @@ -5955,13 +5954,8 @@ int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci) skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN); - 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); - __skb_pull(skb, VLAN_HLEN); + vlan_remove_tag(skb, vlan_tci); - vlan_set_encap_proto(skb, vhdr); skb->mac_header += VLAN_HLEN; if (skb_network_offset(skb) < ETH_HLEN) diff --git a/net/dsa/tag_ocelot.c b/net/dsa/tag_ocelot.c index 73ee09de1a3a..20bf7074d5a6 100644 --- a/net/dsa/tag_ocelot.c +++ b/net/dsa/tag_ocelot.c @@ -30,7 +30,7 @@ static void ocelot_xmit_get_vlan_info(struct sk_buff *skb, struct dsa_port *dp, br_vlan_get_proto(br, &proto); if (ntohs(hdr->h_vlan_proto) == proto) { - __skb_vlan_pop(skb, &tci); + vlan_remove_tag(skb, &tci); *vlan_tci = tci; } else { rcu_read_lock();
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 $ # needed to work around an apparent DSA RX filtering bug $ ip link set $eth promisc on 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 <vladimir.oltean@nxp.com> --- include/linux/if_vlan.h | 20 ++++++++++++++++++++ net/core/skbuff.c | 8 +------- net/dsa/tag_ocelot.c | 2 +- 3 files changed, 22 insertions(+), 8 deletions(-)