CVE-2026-43186

In the Linux kernel, the following vulnerability has been resolved:

ipv6: ioam: fix heap buffer overflow in __ioam6_fill_trace_data()

On the receive path, __ioam6_fill_trace_data() uses trace->nodelen

to decide how much data to write for each node. It trusts this field

as-is from the incoming packet, with no consistency check against

trace->type (the 24-bit field that tells which data items are

present). A crafted packet can set nodelen=0 while setting type bits

0-21, causing the function to write ~100 bytes past the allocated

region (into skb_shared_info), which corrupts adjacent heap memory

and leads to a kernel panic.

Add a shared helper ioam6_trace_compute_nodelen() in ioam6.c to

derive the expected nodelen from the type field, and use it:

- in ioam6_iptunnel.c (send path, existing validation) to replace

the open-coded computation;

- in exthdrs.c (receive path, ipv6_hop_ioam) to drop packets whose

nodelen is inconsistent with the type field, before any data is

written.

Per RFC 9197, bits 12-21 are each short (4-octet) fields, so they

are included in IOAM6_MASK_SHORT_FIELDS (changed from 0xff100000 to

0xff1ffc00).