CVE-2026-64566: xfrm: iptfs: propagate SKBFL_SHARED_FRAG in iptfs_skb_add_frags()

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

xfrm: iptfs: propagate SKBFL_SHARED_FRAG in iptfs_skb_add_frags()

When iptfs_skb_add_frags() copies frag references from the source
frag walk into a new SKB, it increments the page reference count via
__skb_frag_ref() but does not propagate SKBFL_SHARED_FRAG to the
destination SKB's skb_shinfo->flags.

If the source SKB carries shared frags (e.g. from a page-pool backed
receive path), the new inner SKB will appear to ESP as having privately
owned frags.  A subsequent esp_input() call for a nested transport-mode
SA then takes the no-COW fast path and decrypts in place, writing over
pages that are still referenced by the outer IPTFS SKB.  This causes
kernel-visible memory corruption and can trigger a panic.

All other frag-transfer helpers in the kernel (skb_try_coalesce,
skb_gro_receive, __pskb_copy_fclone, skb_shift, skb_segment) correctly
propagate SKBFL_SHARED_FRAG; align iptfs_skb_add_frags() with this
convention by setting the flag inside the loop immediately after
__skb_frag_ref() and nr_frags++, so every exit path that attaches a frag
unconditionally propagates SKBFL_SHARED_FRAG.

The Linux kernel CVE team has assigned CVE-2026-64566 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.14 with commit 5f2b6a9095743a6bf1f34c43c4fe78fa8bdf5ad7 and fixed in 6.18.42 with commit d8aaf06b29f5a0b6186cf68d21c7d63678ee3891
	Issue introduced in 6.14 with commit 5f2b6a9095743a6bf1f34c43c4fe78fa8bdf5ad7 and fixed in 7.1.6 with commit ffd64e0717efd83fbf3396ab4e5ac6d795dac4d0
	Issue introduced in 6.14 with commit 5f2b6a9095743a6bf1f34c43c4fe78fa8bdf5ad7 and fixed in 7.2-rc4 with commit 430ea57d6daf765e88f90046afbfd1e071cb7200

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64566
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/xfrm/xfrm_iptfs.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/d8aaf06b29f5a0b6186cf68d21c7d63678ee3891
	https://git.kernel.org/stable/c/ffd64e0717efd83fbf3396ab4e5ac6d795dac4d0
	https://git.kernel.org/stable/c/430ea57d6daf765e88f90046afbfd1e071cb7200