batman-adv: reject unrepresentable multicast TVLV offsets

Overview

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.

Affected

• Linux >= 07afe1ba288c04280622fa002ed385f1ac0b6fe6 < da1f5aa7ec93f2cc17f5cd30efc54f62af433cf2
• Linux >= 07afe1ba288c04280622fa002ed385f1ac0b6fe6 < 916ec741e65af072b98e475feaad98c063da1b7c
• Linux >= 07afe1ba288c04280622fa002ed385f1ac0b6fe6 < 1b466746fe109127fd983100a228cdd1f1f6ece2
• Linux >= 07afe1ba288c04280622fa002ed385f1ac0b6fe6 < 2b46baa591d0a7c16b62f150917187e70d053be6
• Linux >= 07afe1ba288c04280622fa002ed385f1ac0b6fe6 < f12c2de4f542e3220e17e0606f492110064f04cb
• Linux 6.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.