Tested-by: Chester A. Unal <chester.a.unal@xxxxxxxxxxxxxxxx>
Thanks a ton!
Chester A.
On Mon, Feb 24, 2025 at 6:19 PM Matthieu Baerts (NGI0)
<matttbe@xxxxxxxxxx> wrote:
>
> Before this patch, if the checksum was not used, the subflow was only
> reset if map_data_len was != 0. If there were no MPTCP options or an
> invalid mapping, map_data_len was not set to the data len, and then the
> subflow was not reset as it should have been, leaving the MPTCP
> connection in a wrong fallback mode.
>
> This map_data_len condition has been introduced to handle the reception
> of the infinite mapping. Instead, a new dedicated mapping error could
> have been returned and treated as a special case. However, the commit
> 31bf11de146c ("mptcp: introduce MAPPING_BAD_CSUM") has been introduced
> by Paolo Abeni soon after, and backported later on to stable. It better
> handle the csum case, and it means the exception for valid_csum_seen in
> subflow_can_fallback(), plus this one for the infinite mapping in
> subflow_check_data_avail(), are no longer needed.
>
> In other words, the code can be simplified there: a fallback should only
> be done if msk->allow_infinite_fallback is set. This boolean is set to
> false once MPTCP-specific operations acting on the whole MPTCP
> connection vs the initial path have been done, e.g. a second path has
> been created, or an MPTCP re-injection -- yes, possible even with a
> single subflow. The subflow_can_fallback() helper can then be dropped,
> and replaced by this single condition.
>
> This also makes the code clearer: a fallback should only be done if it
> is possible to do so.
>
> While at it, no need to set map_data_len to 0 in get_mapping_status()
> for the infinite mapping case: it will be set to skb->len just after, at
> the end of subflow_check_data_avail(), and not read in between.
>
> Fixes: f8d4bcacff3b ("mptcp: infinite mapping receiving")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Chester A. Unal <chester.a.unal@xxxxxxxxxxxxxxxx>
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/544
> Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
> ---
> net/mptcp/subflow.c | 15 +--------------
> 1 file changed, 1 insertion(+), 14 deletions(-)
>
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index dfcbef9c46246983d21c827d9551d4eb2c95430e..9f18217dddc865bc467a2c5c34aa4bf23bf3ac75 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -1142,7 +1142,6 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
> if (data_len == 0) {
> pr_debug("infinite mapping received\n");
> MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
> - subflow->map_data_len = 0;
> return MAPPING_INVALID;
> }
>
> @@ -1286,18 +1285,6 @@ static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ss
> mptcp_schedule_work(sk);
> }
>
> -static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)
> -{
> - struct mptcp_sock *msk = mptcp_sk(subflow->conn);
> -
> - if (subflow->mp_join)
> - return false;
> - else if (READ_ONCE(msk->csum_enabled))
> - return !subflow->valid_csum_seen;
> - else
> - return READ_ONCE(msk->allow_infinite_fallback);
> -}
> -
> static void mptcp_subflow_fail(struct mptcp_sock *msk, struct sock *ssk)
> {
> struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
> @@ -1393,7 +1380,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
> return true;
> }
>
> - if (!subflow_can_fallback(subflow) && subflow->map_data_len) {
> + if (!READ_ONCE(msk->allow_infinite_fallback)) {
> /* fatal protocol error, close the socket.
> * subflow_error_report() will introduce the appropriate barriers
> */
>
> --
> 2.47.1
>
