On Fri, Mar 26, 2021 at 11:49 AM Kurt Kanzenbach <k...@linutronix.de> wrote:
>
> Reset MAC header in case of using packet_direct_xmit(), e.g. by specifying
> PACKET_QDISC_BYPASS. This is needed, because other code such as the HSR layer
> expects the MAC header to be correctly set.
>
> This has been observed using the following setup:
>
> |$ ip link add name hsr0 type hsr slave1 lan0 slave2 lan1 supervision 45
> version 1
> |$ ifconfig hsr0 up
> |$ ./test hsr0
>
> The test binary is using mmap'ed sockets and is specifying the
> PACKET_QDISC_BYPASS socket option.
>
> This patch resolves the following warning on a non-patched kernel:
>
> |[ 112.725394] ------------[ cut here ]------------
> |[ 112.731418] WARNING: CPU: 1 PID: 257 at net/hsr/hsr_forward.c:560
> hsr_forward_skb+0x484/0x568
> |[ 112.739962] net/hsr/hsr_forward.c:560: Malformed frame (port_src hsr0)
>
> The MAC header is also reset unconditionally in case of PACKET_QDISC_BYPASS is
> not used.
At the top of __dev_queue_xmit.
I think it is reasonable to expect the mac header to be set in
ndo_start_xmit. Not sure which other devices besides hsr truly
requires it.
> Signed-off-by: Kurt Kanzenbach <k...@linutronix.de>
If this fixes a bug, it should target net.
Fixes: d346a3fae3ff ("packet: introduce PACKET_QDISC_BYPASS socket option")
This change belongs in __dev_direct_xmit unless all callers except
packet_direct_xmit do correctly set the mac header. xsk_generic_xmit
appears to miss it, too, so would equally trigger this warning.
