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