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tipc: prevent snt_unacked underflow on CONN_ACK

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tipc_sk_conn_proto_rcv() subtracts the peer-supplied connection ack count
from the unsigned 16-bit send counter snt_unacked without checking that it
does not exceed the number of messages actually outstanding:

	tsk->snt_unacked -= msg_conn_ack(hdr);

msg_conn_ack() is read straight from a received CONN_MANAGER/CONN_ACK
message. If the ack count is larger than snt_unacked, the subtraction
wraps to a near-maximum value, leaving tsk_conn_cong() permanently true
and starving the connection of further transmits.

Validate the ACK count at the start of the CONN_ACK block and drop the
message if it acknowledges more messages than are outstanding. A peer (or,
for a local connection, the connected peer socket) can otherwise wedge a
TIPC connection's send side by sending an oversized connection ack.

Fixes: 10724cc7bb ("tipc: redesign connection-level flow control")
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
Link: https://patch.msgid.link/20260610124003.3831170-3-michael.bommarito@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Michael Bommarito 2026-06-10 08:40:02 -04:00 committed by Jakub Kicinski
parent 86b0c540e2
commit ab3e10b44b
1 changed files with 3 additions and 0 deletions
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3
net/tipc/socket.c
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@ -1362,6 +1362,9 @@ static void tipc_sk_conn_proto_rcv(struct tipc_sock *tsk, struct sk_buff *skb,
__skb_queue_tail(xmitq, skb);
return;
} else if (mtyp == CONN_ACK) {
if (tsk->snt_unacked < msg_conn_ack(hdr))
goto exit;
was_cong = tsk_conn_cong(tsk);
tipc_sk_push_backlog(tsk, msg_nagle_ack(hdr));
tsk->snt_unacked -= msg_conn_ack(hdr);