Re: [PATCH net v5 8/8] net/mlx5e: psp: tso: replace only the length in checksum seed

[sashiko-bot@kernel.org]

> for psp tcp with tso,
> 
>  - __tcp_transmit_skb() -> tcp_v6_send_check() or tcp_v4_send_check()
>    computes the checksum seed using the addresses on the socket and the
>    total length, then
> 
>  - mlx5e_psp_handle_tx_skb() recomputes the checksum seed using
>    addresses from the packet's l3 header, and the length of one segment
> 
> the length difference is expected by the device. however, the difference
> in addresses is incorrect in cases where the l3 header daddr is an
> intermediate hop, for example,
> 
>  - ipv4 source route option (IP_OPTIONS with lsrr or ssrr)
>  - ipv6 IPV6_RTHDR header (conceptually ; ipv6 extension headers are not
>    properly supported on this path yet)
> 
> in these cases every segment of the tso packet to go out with a bad tcp
> checksum
> 
> the fix is to replace only the length in the seed which tcp had already
> computed. this is also what tcp_gso_segment() does.
> 
> tested on connectx-7, with a psp tcp socket whose ipv4 loose source
> route's first hop isn't the final destination, and the peer checking
> tcp checksums in software.
> 
> Fixes: e5a1861a298e ("net/mlx5e: Implement PSP Tx data path")
> Acked-by: Daniel Zahka <daniel.zahka@gmail.com>
> Signed-off-by: Todd Freed <toddfreed@meta.com>

Sashiko has reviewed this patch and found no issues.

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