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
---
tcp.c | 47 +++++++++++++++++++++++++----------------------
1 file changed, 25 insertions(+), 22 deletions(-)
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;
}
/**
--
2.41.0