[PATCH v3 10/11] icmp: Validate packets received on ping sockets

[David Gibson <david@gibson.dropbear.id.au>]

We access fields of packets received from ping sockets assuming they're
echo replies, without actually checking that.  Of course, we don't expect
anything else from the kernel, but it's probably best to verify.

While we're at it, also check for short packets, or a receive address of
the wrong family.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 icmp.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/icmp.c b/icmp.c
index 79f6c8c..a9dc436 100644
--- a/icmp.c
+++ b/icmp.c
@@ -86,16 +86,25 @@ void icmp_sock_handler(const struct ctx *c, int af, union epoll_ref ref)
 		     pname, strerror(errno));
 		return;
 	}
+	if (sr.sa.sa_family != af)
+		goto unexpected;
 
 	if (af == AF_INET) {
 		struct icmphdr *ih4 = (struct icmphdr *)buf;
 
+		if ((size_t)n < sizeof(*ih4) || ih4->type != ICMP_ECHOREPLY)
+			goto unexpected;
+
 		/* Adjust packet back to guest-side ID */
 		ih4->un.echo.id = htons(ref.icmp.id);
 		seq = ntohs(ih4->un.echo.sequence);
 	} else if (af == AF_INET6) {
 		struct icmp6hdr *ih6 = (struct icmp6hdr *)buf;
 
+		if ((size_t)n < sizeof(*ih6) ||
+		    ih6->icmp6_type != ICMPV6_ECHO_REPLY)
+			goto unexpected;
+
 		/* Adjust packet back to guest-side ID */
 		ih6->icmp6_identifier = htons(ref.icmp.id);
 		seq = ntohs(ih6->icmp6_sequence);
@@ -118,6 +127,10 @@ void icmp_sock_handler(const struct ctx *c, int af, union epoll_ref ref)
 	else if (af == AF_INET6)
 		tap_icmp6_send(c, &sr.sa6.sin6_addr,
 			       tap_ip6_daddr(c, &sr.sa6.sin6_addr), buf, n);
+	return;
+
+unexpected:
+	warn("%s: Unexpected packet on ping socket", pname);
 }
 
 /**
-- 
@@ -86,16 +86,25 @@ void icmp_sock_handler(const struct ctx *c, int af, union epoll_ref ref)
 		     pname, strerror(errno));
 		return;
 	}
+	if (sr.sa.sa_family != af)
+		goto unexpected;
 
 	if (af == AF_INET) {
 		struct icmphdr *ih4 = (struct icmphdr *)buf;
 
+		if ((size_t)n < sizeof(*ih4) || ih4->type != ICMP_ECHOREPLY)
+			goto unexpected;
+
 		/* Adjust packet back to guest-side ID */
 		ih4->un.echo.id = htons(ref.icmp.id);
 		seq = ntohs(ih4->un.echo.sequence);
 	} else if (af == AF_INET6) {
 		struct icmp6hdr *ih6 = (struct icmp6hdr *)buf;
 
+		if ((size_t)n < sizeof(*ih6) ||
+		    ih6->icmp6_type != ICMPV6_ECHO_REPLY)
+			goto unexpected;
+
 		/* Adjust packet back to guest-side ID */
 		ih6->icmp6_identifier = htons(ref.icmp.id);
 		seq = ntohs(ih6->icmp6_sequence);
@@ -118,6 +127,10 @@ void icmp_sock_handler(const struct ctx *c, int af, union epoll_ref ref)
 	else if (af == AF_INET6)
 		tap_icmp6_send(c, &sr.sa6.sin6_addr,
 			       tap_ip6_daddr(c, &sr.sa6.sin6_addr), buf, n);
+	return;
+
+unexpected:
+	warn("%s: Unexpected packet on ping socket", pname);
 }
 
 /**
-- 
2.43.0