On Fri, Apr 10, 2026 at 01:25:39PM +0530, Anshu Kumari wrote:
tcp_send_flag() can return error codes from tcp_prepare_flags() failing TCP_INFO, or from failure to collect buffers on the vhost-user path. These errors indicate the connection requires resetting.
Most callers of tcp_send_flag() were ignoring the error code and carrying on as if nothing was wrong. Check the return value at each call site and handle the error appropriately: - in tcp_data_from_tap(), return -1 so the caller resets - in tcp_tap_handler(), goto reset - in tcp_timer_handler()/tcp_sock_handler()/tcp_conn_from_sock_finish(), call tcp_rst() and return - in tcp_tap_conn_from_sock(), set CLOSING flag (flow not yet active) - in tcp_keepalive(), call tcp_rst() and continue the loop - in tcp_flow_migrate_target_ext(), goto fail
Thanks for this detailed summary, it really helps a reviewer follow the logic.
The call in tcp_rst_do() is left unchecked: we are already resetting, and tcp_sock_rst() still needs to run regardless.
Bug: https://bugs.passt.top/show_bug.cgi?id=194 Signed-off-by: Anshu Kumari
Reviewed-by: David Gibson
--- tcp.c | 59 ++++++++++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 44 insertions(+), 15 deletions(-)
diff --git a/tcp.c b/tcp.c index 8ea9be8..9ce671a 100644 --- a/tcp.c +++ b/tcp.c @@ -1917,7 +1917,9 @@ static int tcp_data_from_tap(const struct ctx *c, struct tcp_tap_conn *conn, "keep-alive sequence: %u, previous: %u", seq, conn->seq_from_tap);
- tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) + return -1; + tcp_timer_ctl(c, conn);
if (setsockopt(conn->sock, SOL_SOCKET, SO_KEEPALIVE, @@ -2043,14 +2045,16 @@ eintr: * Then swiftly looked away and left. */ conn->seq_from_tap = seq_from_tap; - tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) + return -1; }
if (errno == EINTR) goto eintr;
if (errno == EAGAIN || errno == EWOULDBLOCK) { - tcp_send_flag(c, conn, ACK | DUP_ACK); + if (tcp_send_flag(c, conn, ACK | DUP_ACK)) + return -1; return p->count - idx;
} @@ -2070,7 +2074,8 @@ out: */ if (conn->seq_dup_ack_approx != (conn->seq_from_tap & 0xff)) { conn->seq_dup_ack_approx = conn->seq_from_tap & 0xff; - tcp_send_flag(c, conn, ACK | DUP_ACK); + if (tcp_send_flag(c, conn, ACK | DUP_ACK)) + return -1; } return p->count - idx; } @@ -2084,7 +2089,8 @@ out:
conn_event(c, conn, TAP_FIN_RCVD); } else { - tcp_send_flag(c, conn, ACK_IF_NEEDED); + if (tcp_send_flag(c, conn, ACK_IF_NEEDED)) + return -1; }
return p->count - idx; @@ -2122,7 +2128,10 @@ static void tcp_conn_from_sock_finish(const struct ctx *c, return; }
- tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) { + tcp_rst(c, conn); + return; + }
/* The client might have sent data already, which we didn't * dequeue waiting for SYN,ACK from tap -- check now. @@ -2308,7 +2317,9 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, goto reset; }
- tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) + goto reset; + conn_event(c, conn, SOCK_FIN_SENT);
return 1; @@ -2388,7 +2399,9 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, }
conn_event(c, conn, SOCK_FIN_SENT); - tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) + goto reset; + ack_due = 0;
/* If we received a FIN, but the socket is in TCP_ESTABLISHED @@ -2478,7 +2491,11 @@ static void tcp_tap_conn_from_sock(const struct ctx *c, union flow *flow,
conn->wnd_from_tap = WINDOW_DEFAULT;
- tcp_send_flag(c, conn, SYN); + if (tcp_send_flag(c, conn, SYN)) { + conn_flag(c, conn, CLOSING); + return; + } + conn_flag(c, conn, ACK_FROM_TAP_DUE);
tcp_get_sndbuf(conn); @@ -2585,7 +2602,10 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref) return;
if (conn->flags & ACK_TO_TAP_DUE) { - tcp_send_flag(c, conn, ACK_IF_NEEDED); + if (tcp_send_flag(c, conn, ACK_IF_NEEDED)) { + tcp_rst(c, conn); + return; + } tcp_timer_ctl(c, conn); } else if (conn->flags & ACK_FROM_TAP_DUE) { if (!(conn->events & ESTABLISHED)) { @@ -2598,7 +2618,10 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref) tcp_rst(c, conn); } else { flow_trace(conn, "SYN timeout, retry"); - tcp_send_flag(c, conn, SYN); + if (tcp_send_flag(c, conn, SYN)) { + tcp_rst(c, conn); + return; + } conn->retries++; conn_flag(c, conn, SYN_RETRIED); tcp_timer_ctl(c, conn); @@ -2662,8 +2685,11 @@ void tcp_sock_handler(const struct ctx *c, union epoll_ref ref, tcp_data_from_sock(c, conn);
if (events & EPOLLOUT) { - if (tcp_update_seqack_wnd(c, conn, false, NULL)) - tcp_send_flag(c, conn, ACK); + if (tcp_update_seqack_wnd(c, conn, false, NULL) && + tcp_send_flag(c, conn, ACK)) { + tcp_rst(c, conn); + return; + } }
return; @@ -2903,7 +2929,8 @@ static void tcp_keepalive(struct ctx *c, const struct timespec *now) if (conn->tap_inactive) { flow_dbg(conn, "No tap activity for least %us, send keepalive", KEEPALIVE_INTERVAL); - tcp_send_flag(c, conn, KEEPALIVE); + if (tcp_send_flag(c, conn, KEEPALIVE)) + tcp_rst(c, conn); }
/* Ready to check fot next interval */ @@ -3926,7 +3953,9 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd if (tcp_set_peek_offset(conn, peek_offset)) goto fail;
- tcp_send_flag(c, conn, ACK); + if (tcp_send_flag(c, conn, ACK)) + goto fail; + tcp_data_from_sock(c, conn);
if ((rc = tcp_epoll_ctl(conn))) { -- 2.53.0
-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson