From b3f2210b05bc3c5057a6f2a197500df92eb7d71f Mon Sep 17 00:00:00 2001 From: David Gibson Date: Fri, 8 Sep 2023 11:49:52 +1000 Subject: tcp: Consolidate paths where we initiate reset on tap interface There are a number of conditions where we will issue a TCP RST in response to something unexpected we received from the tap interface. These occur in both tcp_data_from_tap() and tcp_tap_handler(). In tcp_tap_handler() use a 'goto out of line' technique to consolidate all these paths into one place. For the tcp_data_from_tap() cases use a negative return code and direct that to the same path in tcp_tap_handler(), its caller. In this case we want to discard all remaining packets in the batch we have received: even if they're otherwise good, they'll be invalidated when the guest receives the RST we're sending. This is subtly different from the case where we *receive* an RST, where we could in theory get a new SYN immediately afterwards. Clarify that with a common on the now common reset path. Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- tcp.c | 47 +++++++++++++++++++++++++---------------------- 1 file changed, 25 insertions(+), 22 deletions(-) (limited to 'tcp.c') diff --git a/tcp.c b/tcp.c index a1b5a72..c76df73 100644 --- a/tcp.c +++ b/tcp.c @@ -2323,17 +2323,13 @@ static int tcp_data_from_tap(struct ctx *c, struct tcp_tap_conn *conn, size_t off; th = packet_get(p, i, 0, sizeof(*th), &len); - if (!th) { - tcp_rst(c, conn); - return p->count - idx; - } + if (!th) + return -1; len += sizeof(*th); off = th->doff * 4UL; - if (off < sizeof(*th) || off > len) { - tcp_rst(c, conn); - return p->count - idx; - } + if (off < sizeof(*th) || off > len) + return -1; if (th->rst) { conn_event(c, conn, CLOSED); @@ -2449,9 +2445,9 @@ eintr: if (errno == EAGAIN || errno == EWOULDBLOCK) { tcp_send_flag(c, conn, ACK_IF_NEEDED); return p->count - idx; + } - tcp_rst(c, conn); - return p->count - idx; + return -1; } if (n < (int)(seq_from_tap - conn->seq_from_tap)) { @@ -2580,20 +2576,18 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, /* Establishing connection from socket */ if (conn->events & SOCK_ACCEPTED) { - if (th->syn && th->ack && !th->fin) + if (th->syn && th->ack && !th->fin) { tcp_conn_from_sock_finish(c, conn, th, opts, optlen); - else - tcp_rst(c, conn); + return 1; + } - return 1; + goto reset; } /* Establishing connection from tap */ if (conn->events & TAP_SYN_RCVD) { - if (!(conn->events & TAP_SYN_ACK_SENT)) { - tcp_rst(c, conn); - return p->count - idx; - } + if (!(conn->events & TAP_SYN_ACK_SENT)) + goto reset; conn_event(c, conn, ESTABLISHED); @@ -2607,10 +2601,8 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, return p->count - idx; } - if (!th->ack) { - tcp_rst(c, conn); - return p->count - idx; - } + if (!th->ack) + goto reset; tcp_clamp_window(c, conn, ntohs(th->window)); @@ -2633,6 +2625,9 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, /* Established connections accepting data from tap */ count = tcp_data_from_tap(c, conn, p, idx); + if (count == -1) + goto reset; + if (conn->seq_ack_to_tap != conn->seq_from_tap) ack_due = 1; @@ -2647,6 +2642,14 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr, conn_flag(c, conn, ACK_TO_TAP_DUE); return count; + +reset: + /* Something's gone wrong, so reset the connection. We discard + * remaining packets in the batch, since they'd be invalidated when our + * RST is received, even if otherwise good. + */ + tcp_rst(c, conn); + return p->count - idx; } /** -- cgit v1.2.3