Subject: CVE-2021-47309: net: validate lwtstate->data before returning from skb_tunnel_info()

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

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

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

net: validate lwtstate->data before returning from skb_tunnel_info()

skb_tunnel_info() returns pointer of lwtstate->data as ip_tunnel_info
type without validation. lwtstate->data can have various types such as
mpls_iptunnel_encap, etc and these are not compatible.
So skb_tunnel_info() should validate before returning that pointer.

Splat looks like:
BUG: KASAN: slab-out-of-bounds in vxlan_get_route+0x418/0x4b0 [vxlan]
Read of size 2 at addr ffff888106ec2698 by task ping/811

CPU: 1 PID: 811 Comm: ping Not tainted 5.13.0+ #1195
Call Trace:
 dump_stack_lvl+0x56/0x7b
 print_address_description.constprop.8.cold.13+0x13/0x2ee
 ? vxlan_get_route+0x418/0x4b0 [vxlan]
 ? vxlan_get_route+0x418/0x4b0 [vxlan]
 kasan_report.cold.14+0x83/0xdf
 ? vxlan_get_route+0x418/0x4b0 [vxlan]
 vxlan_get_route+0x418/0x4b0 [vxlan]
 [ ... ]
 vxlan_xmit_one+0x148b/0x32b0 [vxlan]
 [ ... ]
 vxlan_xmit+0x25c5/0x4780 [vxlan]
 [ ... ]
 dev_hard_start_xmit+0x1ae/0x6e0
 __dev_queue_xmit+0x1f39/0x31a0
 [ ... ]
 neigh_xmit+0x2f9/0x940
 mpls_xmit+0x911/0x1600 [mpls_iptunnel]
 lwtunnel_xmit+0x18f/0x450
 ip_finish_output2+0x867/0x2040
 [ ... ]

The Linux kernel CVE team has assigned CVE-2021-47309 to this issue.

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

	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 4.4.277 with commit e7f3c9df4051
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 4.9.277 with commit b61d327cd3cc
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 4.14.241 with commit 83bdcfbd968b
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 4.19.199 with commit 8bb1589c89e6
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 5.4.135 with commit 8aa13a86964c
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 5.10.53 with commit 2179d96ec702
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 5.13.5 with commit a915379594f1
	Issue introduced in 4.3 with commit 61adedf3e3f1 and fixed in 5.14 with commit 67a9c9431740

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-2021-47309
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:
	include/net/dst_metadata.h

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/e7f3c9df40515a6c6b46f36c4c94cf48a043f887
	https://git.kernel.org/stable/c/b61d327cd3cc5ea591f3bf751dd11e034f388bb5
	https://git.kernel.org/stable/c/83bdcfbd968bcc91a0632b7b625e4a9b0cba5e0d
	https://git.kernel.org/stable/c/8bb1589c89e61e3b182dd546f1021928ebb5c2a6
	https://git.kernel.org/stable/c/8aa13a86964cdec4fd969ef677c6614ff068641a
	https://git.kernel.org/stable/c/2179d96ec702cc33ead02a9ce40ece599b8538c5
	https://git.kernel.org/stable/c/a915379594f1e045421635c6316d8f3ffa018c58
	https://git.kernel.org/stable/c/67a9c94317402b826fc3db32afc8f39336803d97