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tcp: Consolidate paths where we initiate reset on tap interface

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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 <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-09-08 11:49:52 +10:00 committed by Stefano Brivio
parent f984003fdf
commit b3f2210b05
1 changed files with 25 additions and 22 deletions
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47
tcp.c
View file

@ -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;
}
/**