batman-adv: tp_meter: avoid divide-by-zero for dec_cwnd

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63836
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 12:16:57 UTC
Updated2026-07-19 12:16:57 UTC
DescriptionIn 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.

Risk And Classification

EPSS: 0.001650000 probability, percentile 0.060800000 (date 2026-07-20)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e 35264c4d46067d6312871488c810cef387f8c1f6 git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e 1381b021bf886b793fa5ffb895a8efae7ba0318f git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e d08b69da40a101df1e28bfe1e8fa7a09ffa41107 git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e cd74176cf1685f35a2e5f212d15748bbfecb53b6 git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e 7d2a44bc6bbe39aed03c68864aa0e54e04a50278 git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e 585616dab0aa9c45bc11b2c8082ca78533bc00e9 git Not specified
CNA Linux Linux affected 33a3bb4a3345bb511f9c69c913da95d4693e2a4e 33ccd52f3cc9ed46ce395199f89aa3234dc83314 git Not specified
CNA Linux Linux affected 4.8 Not specified
CNA Linux Linux unaffected 4.8 semver Not specified
CNA Linux Linux unaffected 5.10.260 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.211 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.177 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.144 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.95 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.38 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.3 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d08b69da40a101df1e28bfe1e8fa7a09ffa41107 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/33ccd52f3cc9ed46ce395199f89aa3234dc83314 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cd74176cf1685f35a2e5f212d15748bbfecb53b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/35264c4d46067d6312871488c810cef387f8c1f6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/585616dab0aa9c45bc11b2c8082ca78533bc00e9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7d2a44bc6bbe39aed03c68864aa0e54e04a50278 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1381b021bf886b793fa5ffb895a8efae7ba0318f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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