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 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.
