From: aoates@google.com
Date: Sat, 28 Jul 2018 21:54:26 -0400
Message-Id: <20180729015426.67133-1-aoates@google.com>
Subject: [Qemu-devel] [PATCH v2] slirp: fix ICMP handling on macOS hosts
To: qemu-devel@nongnu.org, samuel.thibault@ens-lyon.org, jan.kiszka@siemens.com
Cc: Andrew Oates <aoates@google.com>

From: Andrew Oates <aoates@google.com>

On Linux, SOCK_DGRAM+IPPROTO_ICMP sockets give only the ICMP packet when
read from.  On macOS, however, the socket acts like a SOCK_RAW socket
and includes the IP header as well.

This change strips the extra IP header from the received packet on macOS
before sending it to the guest.

Signed-off-by: Andrew Oates <aoates@google.com>
---
v2: check validity of inner_hlen and update len appropriately

 slirp/ip_icmp.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/slirp/ip_icmp.c b/slirp/ip_icmp.c
index 0b667a429a..76c6d54b11 100644
--- a/slirp/ip_icmp.c
+++ b/slirp/ip_icmp.c
@@ -420,7 +420,21 @@ void icmp_receive(struct socket *so)
     icp = mtod(m, struct icmp *);
 
     id = icp->icmp_id;
-    len = qemu_recv(so->s, icp, m->m_len, 0);
+    len = qemu_recv(so->s, icp, M_ROOM(m), 0);
+#ifdef CONFIG_DARWIN
+    if (len > 0) {
+        /* Skip the IP header that OS X (unlike Linux) includes. */
+        struct ip *inner_ip = mtod(m, struct ip *);
+        int inner_hlen = inner_ip->ip_hl << 2;
+        if (inner_hlen > len) {
+            len = -1;
+            errno = -EINVAL;
+        } else {
+            len -= inner_hlen;
+            memmove(icp, (unsigned char *)icp + inner_hlen, len);
+        }
+    }
+#endif
     icp->icmp_id = id;
 
     m->m_data -= hlen;
-- 
2.17.0