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    Subject[PATCH net-next v3 7/9] net: tcp: add skb drop reasons to tcp tw code path
    Date
    From: Menglong Dong <imagedong@tencent.com>

    In order to get the reasons of skb drops, add a function argument of
    type 'enum skb_drop_reason *reason' to tcp_timewait_state_process().

    In the origin code, all packets to time-wait socket are treated as
    dropping with kfree_skb(), which can make users confused. Therefore,
    we use consume_skb() for the skbs that are 'good'. We can check the
    value of 'reason' to decide use kfree_skb() or consume_skb().

    The new reason 'TIMEWAIT' is added for the case that the skb is dropped
    as the socket in time-wait state.

    Reviewed-by: Jiang Biao <benbjiang@tencent.com>
    Reviewed-by: Hao Peng <flyingpeng@tencent.com>
    Signed-off-by: Menglong Dong <imagedong@tencent.com>
    Reported-by: Eric Dumazet <edumazet@google.com>
    ---
    v2:
    - skb is not freed on TCP_TW_ACK and 'ret' is not initizalized, fix
    it (Eric Dumazet)
    ---
    include/net/dropreason.h | 6 ++++++
    include/net/tcp.h | 7 ++++---
    net/ipv4/tcp_ipv4.c | 9 ++++++++-
    net/ipv4/tcp_minisocks.c | 24 ++++++++++++++++++++----
    net/ipv6/tcp_ipv6.c | 8 +++++++-
    5 files changed, 45 insertions(+), 9 deletions(-)

    diff --git a/include/net/dropreason.h b/include/net/dropreason.h
    index 86e89d3022b5..3c6f8e0f7f16 100644
    --- a/include/net/dropreason.h
    +++ b/include/net/dropreason.h
    @@ -258,6 +258,12 @@ enum skb_drop_reason {
    * socket is full, corresponding to LINUX_MIB_TCPREQQFULLDROP
    */
    SKB_DROP_REASON_TCP_REQQFULLDROP,
    + /**
    + * @SKB_DROP_REASON_TIMEWAIT: socket is in time-wait state and all
    + * packet that received will be treated as 'drop', except a good
    + * 'SYN' packet
    + */
    + SKB_DROP_REASON_TIMEWAIT,
    /**
    * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
    * used as a real 'reason'
    diff --git a/include/net/tcp.h b/include/net/tcp.h
    index 082dd0627e2e..88217b8d95ac 100644
    --- a/include/net/tcp.h
    +++ b/include/net/tcp.h
    @@ -380,9 +380,10 @@ enum tcp_tw_status {
    };


    -enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
    - struct sk_buff *skb,
    - const struct tcphdr *th);
    +enum tcp_tw_status
    +tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    + const struct tcphdr *th,
    + enum skb_drop_reason *reason);
    struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
    struct request_sock *req, bool fastopen,
    bool *lost_race);
    diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
    index 804fc5e0203e..e7bd2f410a4a 100644
    --- a/net/ipv4/tcp_ipv4.c
    +++ b/net/ipv4/tcp_ipv4.c
    @@ -2134,7 +2134,8 @@ int tcp_v4_rcv(struct sk_buff *skb)
    inet_twsk_put(inet_twsk(sk));
    goto csum_error;
    }
    - switch (tcp_timewait_state_process(inet_twsk(sk), skb, th)) {
    + switch (tcp_timewait_state_process(inet_twsk(sk), skb, th,
    + &drop_reason)) {
    case TCP_TW_SYN: {
    struct sock *sk2 = inet_lookup_listener(dev_net(skb->dev),
    &tcp_hashinfo, skb,
    @@ -2150,11 +2151,17 @@ int tcp_v4_rcv(struct sk_buff *skb)
    refcounted = false;
    goto process;
    }
    + /* TCP_FLAGS or NO_SOCKET? */
    + SKB_DR_SET(drop_reason, TCP_FLAGS);
    }
    /* to ACK */
    fallthrough;
    case TCP_TW_ACK:
    tcp_v4_timewait_ack(sk, skb);
    + if (!drop_reason) {
    + consume_skb(skb);
    + return 0;
    + }
    break;
    case TCP_TW_RST:
    tcp_v4_send_reset(sk, skb);
    diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
    index 1a21018f6f64..329724118b7f 100644
    --- a/net/ipv4/tcp_minisocks.c
    +++ b/net/ipv4/tcp_minisocks.c
    @@ -83,13 +83,15 @@ tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw,
    */
    enum tcp_tw_status
    tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    - const struct tcphdr *th)
    + const struct tcphdr *th,
    + enum skb_drop_reason *reason)
    {
    struct tcp_options_received tmp_opt;
    struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
    bool paws_reject = false;

    tmp_opt.saw_tstamp = 0;
    + *reason = SKB_DROP_REASON_NOT_SPECIFIED;
    if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) {
    tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL);

    @@ -113,11 +115,16 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    return tcp_timewait_check_oow_rate_limit(
    tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2);

    - if (th->rst)
    + if (th->rst) {
    + SKB_DR_SET(*reason, TCP_RESET);
    goto kill;
    + }

    - if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt))
    + if (th->syn && !before(TCP_SKB_CB(skb)->seq,
    + tcptw->tw_rcv_nxt)) {
    + SKB_DR_SET(*reason, TCP_FLAGS);
    return TCP_TW_RST;
    + }

    /* Dup ACK? */
    if (!th->ack ||
    @@ -143,6 +150,9 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    }

    inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);
    +
    + /* skb should be free normally on this case. */
    + *reason = SKB_NOT_DROPPED_YET;
    return TCP_TW_ACK;
    }

    @@ -174,6 +184,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    * protocol bug yet.
    */
    if (twsk_net(tw)->ipv4.sysctl_tcp_rfc1337 == 0) {
    + SKB_DR_SET(*reason, TCP_RESET);
    kill:
    inet_twsk_deschedule_put(tw);
    return TCP_TW_SUCCESS;
    @@ -216,11 +227,14 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    if (isn == 0)
    isn++;
    TCP_SKB_CB(skb)->tcp_tw_isn = isn;
    + *reason = SKB_NOT_DROPPED_YET;
    return TCP_TW_SYN;
    }

    - if (paws_reject)
    + if (paws_reject) {
    + SKB_DR_SET(*reason, TCP_RFC7323_PAWS);
    __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED);
    + }

    if (!th->rst) {
    /* In this case we must reset the TIMEWAIT timer.
    @@ -232,9 +246,11 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
    if (paws_reject || th->ack)
    inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN);

    + SKB_DR_OR(*reason, TIMEWAIT);
    return tcp_timewait_check_oow_rate_limit(
    tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
    }
    + SKB_DR_SET(*reason, TCP_RESET);
    inet_twsk_put(tw);
    return TCP_TW_SUCCESS;
    }
    diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
    index 0d2ba9d90529..41551a3b679b 100644
    --- a/net/ipv6/tcp_ipv6.c
    +++ b/net/ipv6/tcp_ipv6.c
    @@ -1795,7 +1795,8 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
    goto csum_error;
    }

    - switch (tcp_timewait_state_process(inet_twsk(sk), skb, th)) {
    + switch (tcp_timewait_state_process(inet_twsk(sk), skb, th,
    + &drop_reason)) {
    case TCP_TW_SYN:
    {
    struct sock *sk2;
    @@ -1815,11 +1816,16 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
    refcounted = false;
    goto process;
    }
    + SKB_DR_SET(drop_reason, TCP_FLAGS);
    }
    /* to ACK */
    fallthrough;
    case TCP_TW_ACK:
    tcp_v6_timewait_ack(sk, skb);
    + if (!drop_reason) {
    + consume_skb(skb);
    + return 0;
    + }
    break;
    case TCP_TW_RST:
    tcp_v6_send_reset(sk, skb);
    --
    2.36.1
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