[PATCH net] inet: RAW sockets using IPPROTO_RAW MUST drop incoming ICMP

[Eric Dumazet <edumazet@google.com>]

Yizhou Zhao reported that simply having one RAW socket on protocol
IPPROTO_RAW (255) was dangerous.

  socket(AF_INET, SOCK_RAW, 255);

A malicious incoming ICMP packet can set the protocol field to 255
and match this socket, leading to FNHE cache changes.

inner = IP(src="192.168.2.1", dst="8.8.8.8", proto=255)/Raw("TEST")
pkt = IP(src="192.168.1.1", dst="192.168.2.1")/ICMP(type=3, code=4, nexthopmtu=576)/inner

"man 7 raw" states:

  A protocol of IPPROTO_RAW implies enabled IP_HDRINCL and is able
  to send any IP protocol that is specified in the passed header.
  Receiving of all IP protocols via IPPROTO_RAW is not possible
  using raw sockets.

Make sure we drop these malicious packets.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Link: https://lore.kernel.org/netdev/20251109134600.292125-1-zhaoyz24@mails.tsinghua.edu.cn/
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
Cc: Ido Schimmel <idosch@nvidia.com>
Cc: David Ahern <dsahern@kernel.org>
---
 net/ipv4/icmp.c | 14 ++++++++++----
 net/ipv6/icmp.c |  6 ++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 4abbec2f47ef58242b686f411109494e40c8d752..4acbbc703e79807ba847a53954952f85dc325499 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -1031,16 +1031,22 @@ static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
 	/* Checkin full IP header plus 8 bytes of protocol to
 	 * avoid additional coding at protocol handlers.
 	 */
-	if (!pskb_may_pull(skb, iph->ihl * 4 + 8)) {
-		__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
-		return;
-	}
+	if (!pskb_may_pull(skb, iph->ihl * 4 + 8))
+		goto out;
+
+	/* IPPROTO_RAW sockets are not supposed to receive anything. */
+	if (protocol == IPPROTO_RAW)
+		goto out;
 
 	raw_icmp_error(skb, protocol, info);
 
 	ipprot = rcu_dereference(inet_protos[protocol]);
 	if (ipprot && ipprot->err_handler)
 		ipprot->err_handler(skb, info);
+	return;
+
+out:
+	__ICMP_INC_STATS(dev_net_rcu(skb->dev), ICMP_MIB_INERRORS);
 }
 
 static bool icmp_tag_validation(int proto)
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 9d37e7711bc2b8f12c5c2e24b76378c4f3bf401b..a77f3113ef23b6e42743600e7dab5b2e088cd5dd 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -1066,6 +1066,12 @@ enum skb_drop_reason icmpv6_notify(struct sk_buff *skb, u8 type,
 	if (reason != SKB_NOT_DROPPED_YET)
 		goto out;
 
+	if (nexthdr == IPPROTO_RAW) {
+		/* Add a more specific reason later ? */
+		reason = SKB_DROP_REASON_NOT_SPECIFIED;
+		goto out;
+	}
+
 	/* BUGGG_FUTURE: we should try to parse exthdrs in this packet.
 	   Without this we will not able f.e. to make source routed
 	   pmtu discovery.
-- 
2.53.0.rc2.204.g2597b5adb4-goog