CVE-2026-97965: vxlan: initialize _md in vxlan_xmit_one()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

vxlan: initialize _md in vxlan_xmit_one()

If a VXLAN device is configured with both VXLAN_F_COLLECT_METADATA and
VXLAN_F_GBP, and a packet is transmitted through it using an external
ip_tunnel_info that lacks the IP_TUNNEL_VXLAN_OPT_BIT flag, md is left
pointing to the uninitialized _md stack variable:

                if (test_bit(IP_TUNNEL_VXLAN_OPT_BIT, info->key.tun_flags)) {
                        if (info->options_len < sizeof(*md))
                                goto drop;
                        md = ip_tunnel_info_opts(info);
                }

Because IP_TUNNEL_VXLAN_OPT_BIT is not set, md is not updated and remains
pointing to _md. Later, vxlan_build_skb() is called with md, which
eventually calls vxlan_build_gbp_hdr():

        if (vxflags & VXLAN_F_GBP)
                vxlan_build_gbp_hdr(vxh, md);

Inside vxlan_build_gbp_hdr(), md->gbp is read:

        if (!md->gbp)
                return;
        gbp = (struct vxlanhdr_gbp *)vxh;
        ...
        if (md->gbp & VXLAN_GBP_DONT_LEARN)
                gbp->dont_learn = 1;

If the stack contains garbage, this causes:
1) VXLAN_HF_GBP flag to be spuriously set in the VXLAN header.
2) gbp->dont_learn and gbp->policy_applied to be set from stack bits.
3) gbp->policy_id to receive 16 bits of uninitialized kernel stack data,
   leaking it onto the wire.

Fix this by zero-initializing _md. If IP_TUNNEL_VXLAN_OPT_BIT is not
present, md->gbp remains 0, and vxlan_build_gbp_hdr() returns early
without modifying the VXLAN header.

The Linux kernel CVE team has assigned CVE-2026-97965 to this issue.


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

	Issue introduced in 4.3 with commit ee122c79d4227f6ec642157834b6a90fcffa4382 and fixed in 6.12.111 with commit 0d13b5a413bffc8718b3821b78537ccc6596c233
	Issue introduced in 4.3 with commit ee122c79d4227f6ec642157834b6a90fcffa4382 and fixed in 6.18.53 with commit bfb74c48ac2d31476d5e09cf9658844508d2608a
	Issue introduced in 4.3 with commit ee122c79d4227f6ec642157834b6a90fcffa4382 and fixed in 7.2.7 with commit 081f22177d9d12b1e381b787f203cd5f47508187
	Issue introduced in 4.3 with commit ee122c79d4227f6ec642157834b6a90fcffa4382 and fixed in 7.3-rc3 with commit be83178bfc44588f6e3adb827ed874c683193466

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-2026-97965
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:
	drivers/net/vxlan/vxlan_core.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/0d13b5a413bffc8718b3821b78537ccc6596c233
	https://git.kernel.org/stable/c/bfb74c48ac2d31476d5e09cf9658844508d2608a
	https://git.kernel.org/stable/c/081f22177d9d12b1e381b787f203cd5f47508187
	https://git.kernel.org/stable/c/be83178bfc44588f6e3adb827ed874c683193466