The GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements bc_ackers on every inbound group ACK, even when the same member has already acknowledged the current broadcast round. Because bc_ackers is a u16, a duplicate ACK received after the last legitimate ACK wraps the counter to 65535. Once wrapped, tipc_group_bc_cong() keeps reporting congestion and later group broadcasts on the affected socket stay blocked until the group is recreated. Fix this by ignoring duplicate or stale ACKs before touching bc_acked or bc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and prevents the underflow path. Fixes: 2f487712b893 ("tipc: guarantee that group broadcast doesn't bypass group unicast") Cc: stable@vger.kernel.org Signed-off-by: Oleh Konko --- v3: - correct the Fixes tag to the commit that introduced GRP_ACK_MSG and bc_ackers v2: - make duplicate or stale GRP_ACK_MSG a full no-op via early return - place acked in reverse xmas tree style net/tipc/group.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/tipc/group.c b/net/tipc/group.c index e0e6227b433..14e6732624e 100644 --- a/net/tipc/group.c +++ b/net/tipc/group.c @@ -746,6 +746,7 @@ void tipc_group_proto_rcv(struct tipc_group *grp, bool *usr_wakeup, u32 port = msg_origport(hdr); struct tipc_member *m, *pm; u16 remitted, in_flight; + u16 acked; if (!grp) return; @@ -798,7 +799,10 @@ void tipc_group_proto_rcv(struct tipc_group *grp, bool *usr_wakeup, case GRP_ACK_MSG: if (!m) return; - m->bc_acked = msg_grp_bc_acked(hdr); + acked = msg_grp_bc_acked(hdr); + if (less_eq(acked, m->bc_acked)) + return; + m->bc_acked = acked; if (--grp->bc_ackers) return; list_del_init(&m->small_win); -- 2.50.0