CVE-2026-80839

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CVE-2026-80839

Summary: batman-adv: reject unrepresentable multicast TVLV offsets

Details: In the Linux kernel, the following vulnerability has been resolved: batman-adv: reject unrepresentable multicast TVLV offsets The network and transport header fields in struct sk_buff are 16-bit offsets from skb->head, and U16_MAX is reserved as the unset transport header value. batadv_tvlv_call_handler() sets both fields from a received multicast TVLV without checking whether the TVLV end is representable. If the end offset exceeds the field's range, skb_set_transport_header() truncates it so that the transport header precedes the network header. The negative difference is then returned by skb_network_header_len() as a large u32. batadv_mcast_forw_packet() consequently accepts an oversized multicast tracker and accesses memory beyond the skb data. Add skb_set_transport_header_careful(), an offset-aware counterpart to skb_reset_transport_header_careful(), which validates the final head-relative offset before assigning it. Use the new helper in batadv_tvlv_call_handler() and reject unrepresentable TVLVs before setting the network header.

References: https://git.kernel.org/stable/c/1b466746fe109127fd983100a228cdd1f1f6ece2, https://git.kernel.org/stable/c/2b46baa591d0a7c16b62f150917187e70d053be6, https://git.kernel.org/stable/c/916ec741e65af072b98e475feaad98c063da1b7c, https://git.kernel.org/stable/c/da1f5aa7ec93f2cc17f5cd30efc54f62af433cf2, https://git.kernel.org/stable/c/f12c2de4f542e3220e17e0606f492110064f04cb, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80839.json, https://nvd.nist.gov/vuln/detail/CVE-2026-80839, https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git