CVE-2026-64132

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

ipv6: ioam: refresh hdr pointer before ioam6_event()

Reported by Sashiko:

In ipv6_hop_ioam(), the hdr pointer is initialized to point into the skbs linear data buffer. Later, the code calls skb_ensure_writable(), which might reallocate the buffer:

if (skb_ensure_writable(skb, optoff + 2 + hdr->opt_len))
	goto drop;

/* Trace pointer may have changed */
trace = (struct ioam6_trace_hdr *)(skb_network_header(skb)
				   + optoff + sizeof(*hdr));

ioam6_fill_trace_data(skb, ns, trace, true);

ioam6_event(IOAM6_EVENT_TRACE, dev_net(skb->dev),
	    GFP_ATOMIC, (void *)trace, hdr->opt_len - 2);

If the skb is cloned or lacks sufficient linear headroom, skb_ensure_writable() will invoke pskb_expand_head(), which reallocates the skbs data buffer and frees the old one, invalidating pointers to it. While the code recalculates the trace pointer immediately after the call to skb_ensure_writable(), it fails to recalculate the hdr pointer.

This patch fixes the above by recalculating the hdr pointer before passing hdr->opt_len to ioam6_event(), so that we avoid any UaF.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/24de676da63c1122d2c13b0d546238b66d1b4e62
• https://git.kernel.org/stable/c/5af905aa8e91ff8d94572a1e089558f21dcf24ed
• https://git.kernel.org/stable/c/769723124b7c3b2bfea4cf68ad292698b87c8d01
• https://git.kernel.org/stable/c/e46e6bc97fb1f339730ff1ba74267fbf48e7a422