From 3a0a96500a5779c235faf1dc2332a4b2b3aa89e5 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Fri, 26 Jun 2026 18:11:02 +0200 Subject: [PATCH] batman-adv: tp_meter: avoid window underflow commit 765947b81fb54b6ebb0bc1cfe55c0fa399e002b8 upstream. In batadv_tp_avail(), win_left is calculated with 32-bit unsigned arithmetic: win_left = win_limit - tp_vars->last_sent; During Fast Recovery, cwnd is inflated and last_sent advances rapidly. When Fast Recovery ends, cwnd drops abruptly back to ss_threshold. If the newly shrunk win_limit is less than last_sent, the unsigned subtraction will underflow, wrapping to a massive positive value. Instead of returning that the window is full (unavailable), it returns that the sender can continue sending. To handle this situation, it must be checked whether the windows end sequence number (win_limit) has to be compared with the last sent sequence number. If it would be before the last sent sequence number, then more acks are needed before the transmission can be started again. Cc: stable@kernel.org Fixes: 33a3bb4a3345 ("batman-adv: throughput meter implementation") Signed-off-by: Sven Eckelmann Signed-off-by: Sasha Levin --- net/batman-adv/tp_meter.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/batman-adv/tp_meter.c b/net/batman-adv/tp_meter.c index f6ccb639744a..0fdcafca3aa0 100644 --- a/net/batman-adv/tp_meter.c +++ b/net/batman-adv/tp_meter.c @@ -817,10 +817,15 @@ out: static bool batadv_tp_avail(struct batadv_tp_vars *tp_vars, size_t payload_len) { + u32 last_sent = READ_ONCE(tp_vars->last_sent); u32 win_left, win_limit; win_limit = atomic_read(&tp_vars->last_acked) + tp_vars->cwnd; - win_left = win_limit - tp_vars->last_sent; + + if (batadv_seq_before(last_sent, win_limit)) + win_left = win_limit - last_sent; + else + win_left = 0; return win_left >= payload_len; }