netfilter: nfnetlink_queue: fix OOB when mac header was cleared

BugLink: https://bugs.launchpad.net/bugs/1953387
[ Upstream commit 5648b5e1169ff1d6d6a46c35c0b5fbebd2a5cbb2 ]

On 64bit platforms the MAC header is set to 0xffff on allocation and
also when a helper like skb_unset_mac_header() is called.

dev_parse_header may call skb_mac_header() which assumes valid mac offset:

 BUG: KASAN: use-after-free in eth_header_parse+0x75/0x90
 Read of size 6 at addr ffff8881075a5c05 by task nf-queue/1364
 Call Trace:
  memcpy+0x20/0x60
  eth_header_parse+0x75/0x90
  __nfqnl_enqueue_packet+0x1a61/0x3380
  __nf_queue+0x597/0x1300
  nf_queue+0xf/0x40
  nf_hook_slow+0xed/0x190
  nf_hook+0x184/0x440
  ip_output+0x1c0/0x2a0
  nf_reinject+0x26f/0x700
  nfqnl_recv_verdict+0xa16/0x18b0
  nfnetlink_rcv_msg+0x506/0xe70

The existing code only works if the skb has a mac header.

Fixes: 2c38de4c1f8da7 ("netfilter: fix looped (broad|multi)cast's MAC handling")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 6f0a2bad8ad5eecc4add1b56e08ae5b3b2b19a60..a8cb562da3feaf32218697344bbc09884ec8976e 100644 (file)
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -562,7 +562,7 @@ nfqnl_build_packet_message(struct net *net, struct nfqnl_instance *queue,
                goto nla_put_failure;
 
        if (indev && entskb->dev &&
-           entskb->mac_header != entskb->network_header) {
+           skb_mac_header_was_set(entskb)) {
                struct nfqnl_msg_packet_hw phw;
                int len;