CVE-2026-63836

01/Description

In the Linux kernel, the following vulnerability has been resolved: batman-adv: tp_meter: avoid divide-by-zero for dec_cwnd The cwnd is always MSS <= cwnd <= 0x20000000. But the calculation in batadv_tp_update_cwnd() assumes unsigned 32 bit arithmetics. ((mss * 8) ** 2) / (cwnd * 8) In case cwnd is actually 0x20000000, it will be shifted by 3 bit to the left end up at 0x100000000 or U32_MAX + 1. It will therefore wrap around and be 0 - resulting in: ((mss * 8) ** 2) / 0 This is of course invalid and cannot be calculated. The calculation should must be simplified to avoid this overflow: (mss ** 2) * 8 / cwnd It will keep the precision enhancement from the scaling (by 8) but avoid the overflow in the divisor. In theory, there could still be an overflow in the dividend. It is at the moment fixed to BATADV_TP_PLEN in batadv_tp_recv_ack() - so it is not an imminent problem. But allowing it to use the whole u32 bit range, would mean that it can still use up to 67 bits. To keep this calculation safe for 32 bit arithmetic, mss must never use more than floor((32 - 3) / 2) bits - or in other words: must never be larger than 16383.

02/Affected products

linux: linux kernel

03/References8

• git.kernel.org/stable/c/1381b021bf886b793fa5ffb895a8efae7ba0318f Patch
• git.kernel.org/stable/c/33ccd52f3cc9ed46ce395199f89aa3234dc83314 Patch
• git.kernel.org/stable/c/35264c4d46067d6312871488c810cef387f8c1f6 Patch
• git.kernel.org/stable/c/585616dab0aa9c45bc11b2c8082ca78533bc00e9 Patch
• git.kernel.org/stable/c/7d2a44bc6bbe39aed03c68864aa0e54e04a50278 Patch
• git.kernel.org/stable/c/ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f Patch
• git.kernel.org/stable/c/cd74176cf1685f35a2e5f212d15748bbfecb53b6 Patch
• git.kernel.org/stable/c/d08b69da40a101df1e28bfe1e8fa7a09ffa41107 Patch