[PATCH net 2/2] ipmr, ip6mr: validate packets injected into the register vif on xmit

[Ido Schimmel <idosch@nvidia.com>]

reg_vif_xmit() passes the packet to ipmr_cache_report() which copies its
IP header into the IGMPMSG_WHOLEPKT report that is queued to the mroute
socket. Nothing guarantees that the packet contains a full IP header, so
when a short packet is injected on the register device (e.g., using
AF_PACKET), the copy reads past the end of the packet and a recvmsg() on
the mroute socket leaks the uninitialized bytes to user space [1].

IPv6 has the same problem [2]. Its reg_vif_xmit() does call
pskb_inet_may_pull(), but the helper keys off skb->protocol and does not
pull anything when the protocol is neither IPv4 nor IPv6.

Fix by dropping packets whose protocol does not match the address family
of the register device or that do not contain a full network header.

[1]
BUG: KMSAN: kernel-infoleak in _copy_to_iter
 raw_recvmsg

Uninit was stored to memory at:
 ipmr_cache_report
 reg_vif_xmit
 packet_sendmsg

Uninit was created at:
 __alloc_skb
 sock_alloc_send_pskb
 packet_sendmsg

Bytes 1-3 of 21 are uninitialized

[2]
BUG: KMSAN: kernel-infoleak in _copy_to_iter
 rawv6_recvmsg

Uninit was stored to memory at:
 ip6mr_cache_report
 reg_vif_xmit
 packet_sendmsg

Uninit was created at:
 __alloc_skb
 sock_alloc_send_pskb
 packet_sendmsg

Bytes 8-23 of 41 are uninitialized

Fixes: 14fb64e1f449 ("[IPV6] MROUTE: Support PIM-SM (SSM).")
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <netdev-bot+sashiko@kernel.org>
Closes: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/0545f0c83f5ee2f6696210f87268e811ef655715.1792476357.git.zhilinz%40nebusec.ai
Assisted-by: LLM
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
 net/ipv4/ipmr.c  | 6 ++++++
 net/ipv6/ip6mr.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index eac23f251bfd..d6691c917af4 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -539,6 +539,12 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb, struct net_device *dev)
 	};
 	int err;
 
+	if (skb->protocol != htons(ETH_P_IP) || !pskb_inet_may_pull(skb)) {
+		DEV_STATS_INC(dev, tx_errors);
+		kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+
 	rcu_read_lock();
 	err = ipmr_fib_lookup(net, &fl4, &mrt);
 	if (err < 0) {
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 3a551be30f15..a628acf50b0d 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -642,7 +642,7 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb,
 		.flowi6_mark	= skb->mark,
 	};
 
-	if (!pskb_inet_may_pull(skb))
+	if (skb->protocol != htons(ETH_P_IPV6) || !pskb_inet_may_pull(skb))
 		goto tx_err;
 
 	rcu_read_lock();
-- 
2.56.0