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tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG

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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: 2f487712b8 ("tipc: guarantee that group broadcast doesn't bypass group unicast")
Cc: stable@vger.kernel.org
Signed-off-by: Oleh Konko <security@1seal.org>
Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/41a4833f368641218e444fdcff822039.security@1seal.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Oleh Konko
2026-04-02 09:48:57 +00:00
committed by Jakub Kicinski
parent 7b735ef812
commit 48a5fe3877
1 changed files with 5 additions and 1 deletions
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6
net/tipc/group.c
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@@ -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);