slirp: Factorizing tcpiphdr structure with an union

This patch factorizes the tcpiphdr structure to put the IPv4 fields in
an union, for addition of version 6 in further patch.
Using some macros, retrocompatibility of the existing code is assured.

This patch also fixes the SLIRP_MSIZE and margin computation in various
functions, and makes them compatible with the new tcpiphdr structure,
whose size will be bigger than sizeof(struct tcphdr) + sizeof(struct ip)

Signed-off-by: Guillaume Subiron <maethor@subiron.org>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>

8 files changed, 106 insertions, 45 deletions

diff --git a/slirp/if.h b/slirp/if.h
index 3327023..c7a5c57 100644
--- a/slirp/if.h
+++ b/slirp/if.h
@@ -17,7 +17,7 @@
 #define IF_MRU 1500
 #define	IF_COMP IF_AUTOCOMP	/* Flags for compression */
 
-/* 2 for alignment, 14 for ethernet, 40 for TCP/IP */
-#define IF_MAXLINKHDR (2 + 14 + 40)
+/* 2 for alignment, 14 for ethernet */
+#define IF_MAXLINKHDR (2 + ETH_HLEN)
 
 #endif
diff --git a/slirp/mbuf.c b/slirp/mbuf.c
index c959758..d688dd4 100644
--- a/slirp/mbuf.c
+++ b/slirp/mbuf.c
@@ -22,9 +22,9 @@
 
 /*
  * Find a nice value for msize
- * XXX if_maxlinkhdr already in mtu
  */
-#define SLIRP_MSIZE (IF_MTU + IF_MAXLINKHDR + offsetof(struct mbuf, m_dat) + 6)
+#define SLIRP_MSIZE\
+    (offsetof(struct mbuf, m_dat) + IF_MAXLINKHDR + TCPIPHDR_DELTA + IF_MTU)
 
 void
 m_init(Slirp *slirp)
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 049c2cf..dd4f6d2 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -766,15 +766,16 @@ void slirp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
         m = m_get(slirp);
         if (!m)
             return;
-        /* Note: we add to align the IP header */
-        if (M_FREEROOM(m) < pkt_len + 2) {
-            m_inc(m, pkt_len + 2);
+        /* Note: we add 2 to align the IP header on 4 bytes,
+         * and add the margin for the tcpiphdr overhead  */
+        if (M_FREEROOM(m) < pkt_len + TCPIPHDR_DELTA + 2) {
+            m_inc(m, pkt_len + TCPIPHDR_DELTA + 2);
         }
-        m->m_len = pkt_len + 2;
-        memcpy(m->m_data + 2, pkt, pkt_len);
+        m->m_len = pkt_len + TCPIPHDR_DELTA + 2;
+        memcpy(m->m_data + TCPIPHDR_DELTA + 2, pkt, pkt_len);
 
-        m->m_data += 2 + ETH_HLEN;
-        m->m_len -= 2 + ETH_HLEN;
+        m->m_data += TCPIPHDR_DELTA + 2 + ETH_HLEN;
+        m->m_len -= TCPIPHDR_DELTA + 2 + ETH_HLEN;
 
         if (proto == ETH_P_IP) {
             ip_input(m);
diff --git a/slirp/socket.c b/slirp/socket.c
index 55150f5..8df9252 100644
--- a/slirp/socket.c
+++ b/slirp/socket.c
@@ -483,7 +483,18 @@ sorecvfrom(struct socket *so)
 	  if (!m) {
 	      return;
 	  }
-	  m->m_data += IF_MAXLINKHDR;
+	  switch (so->so_ffamily) {
+	  case AF_INET:
+	      m->m_data += IF_MAXLINKHDR + sizeof(struct udpiphdr);
+	      break;
+	  case AF_INET6:
+	      m->m_data += IF_MAXLINKHDR + sizeof(struct ip6)
+	                                 + sizeof(struct udphdr);
+	      break;
+	  default:
+	      g_assert_not_reached();
+	      break;
+	  }
 
 	  /*
 	   * XXX Shouldn't FIONREAD packets destined for port 53,
diff --git a/slirp/tcp_input.c b/slirp/tcp_input.c
index 117a66e..640dd79 100644
--- a/slirp/tcp_input.c
+++ b/slirp/tcp_input.c
@@ -256,11 +256,6 @@ tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
 	}
 	slirp = m->slirp;
 
-	/*
-	 * Get IP and TCP header together in first mbuf.
-	 * Note: IP leaves IP header in first mbuf.
-	 */
-	ti = mtod(m, struct tcpiphdr *);
 	if (iphlen > sizeof(struct ip )) {
 	  ip_stripoptions(m, (struct mbuf *)0);
 	  iphlen=sizeof(struct ip );
@@ -277,14 +272,28 @@ tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
 	save_ip.ip_len+= iphlen;
 
 	/*
+	 * Get IP and TCP header together in first mbuf.
+	 * Note: IP leaves IP header in first mbuf.
+	 */
+	m->m_data -= sizeof(struct tcpiphdr) - sizeof(struct ip)
+	                                     - sizeof(struct tcphdr);
+	m->m_len += sizeof(struct tcpiphdr) - sizeof(struct ip)
+	                                    - sizeof(struct tcphdr);
+	ti = mtod(m, struct tcpiphdr *);
+
+	/*
 	 * Checksum extended TCP header and data.
 	 */
-	tlen = ((struct ip *)ti)->ip_len;
-        tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
-        memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
-	ti->ti_x1 = 0;
+	tlen = ip->ip_len;
+	tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
+	memset(&ti->ih_mbuf, 0 , sizeof(struct mbuf_ptr));
+	memset(&ti->ti, 0, sizeof(ti->ti));
+	ti->ti_x0 = 0;
+	ti->ti_src = save_ip.ip_src;
+	ti->ti_dst = save_ip.ip_dst;
+	ti->ti_pr = save_ip.ip_p;
 	ti->ti_len = htons((uint16_t)tlen);
-	len = sizeof(struct ip ) + tlen;
+	len = ((sizeof(struct tcpiphdr) - sizeof(struct tcphdr)) + tlen);
 	if(cksum(m, len)) {
 	  goto drop;
 	}
@@ -603,6 +612,10 @@ findso:
 	      HTONS(ti->ti_urp);
 	      m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 	      m->m_len  += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
+	      m->m_data += sizeof(struct tcpiphdr) - sizeof(struct ip)
+						   - sizeof(struct tcphdr);
+	      m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct ip)
+						   - sizeof(struct tcphdr);
 	      *ip=save_ip;
 	      icmp_send_error(m, ICMP_UNREACH, code, 0, strerror(errno));
 	    }
@@ -1471,7 +1484,7 @@ tcp_mss(struct tcpcb *tp, u_int offer)
 	DEBUG_ARG("tp = %p", tp);
 	DEBUG_ARG("offer = %d", offer);
 
-	mss = min(IF_MTU, IF_MRU) - sizeof(struct tcpiphdr);
+	mss = min(IF_MTU, IF_MRU) - sizeof(struct tcphdr) + sizeof(struct ip);
 	if (offer)
 		mss = min(mss, offer);
 	mss = max(mss, 32);
diff --git a/slirp/tcp_output.c b/slirp/tcp_output.c
index 34e4d2e..7fc6a87 100644
--- a/slirp/tcp_output.c
+++ b/slirp/tcp_output.c
@@ -448,15 +448,23 @@ send:
 	 */
 	m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
 
-    {
+	struct tcpiphdr tcpiph_save = *(mtod(m, struct tcpiphdr *));
+	m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
+	                                     - sizeof(struct ip);
+	m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
+	                                     - sizeof(struct ip);
+	struct ip *ip = mtod(m, struct ip *);
 
-	((struct ip *)ti)->ip_len = m->m_len;
+	ip->ip_len = m->m_len;
+	ip->ip_dst = tcpiph_save.ti_dst;
+	ip->ip_src = tcpiph_save.ti_src;
+	ip->ip_p = tcpiph_save.ti_pr;
 
-	((struct ip *)ti)->ip_ttl = IPDEFTTL;
-	((struct ip *)ti)->ip_tos = so->so_iptos;
+	ip->ip_ttl = IPDEFTTL;
+	ip->ip_tos = so->so_iptos;
 
 	error = ip_output(so, m);
-    }
+
 	if (error) {
 out:
 		return (error);
diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
index b1aa1f2..cd021df 100644
--- a/slirp/tcp_subr.c
+++ b/slirp/tcp_subr.c
@@ -76,9 +76,10 @@ tcp_template(struct tcpcb *tp)
 	register struct tcpiphdr *n = &tp->t_template;
 
 	n->ti_mbuf = NULL;
-	n->ti_x1 = 0;
+	memset(&n->ti, 0, sizeof(n->ti));
+	n->ti_x0 = 0;
 	n->ti_pr = IPPROTO_TCP;
-	n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
+	n->ti_len = htons(sizeof(struct tcphdr));
 	n->ti_src = so->so_faddr;
 	n->ti_dst = so->so_laddr;
 	n->ti_sport = so->so_fport;
@@ -131,6 +132,7 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
 		m->m_data += IF_MAXLINKHDR;
 		*mtod(m, struct tcpiphdr *) = *ti;
 		ti = mtod(m, struct tcpiphdr *);
+		memset(&ti->ti, 0, sizeof(ti->ti));
 		flags = TH_ACK;
 	} else {
 		/*
@@ -150,8 +152,8 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
 	tlen += sizeof (struct tcpiphdr);
 	m->m_len = tlen;
 
-        ti->ti_mbuf = NULL;
-	ti->ti_x1 = 0;
+	ti->ti_mbuf = NULL;
+	ti->ti_x0 = 0;
 	ti->ti_seq = htonl(seq);
 	ti->ti_ack = htonl(ack);
 	ti->ti_x2 = 0;
@@ -164,12 +166,23 @@ tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
 	ti->ti_urp = 0;
 	ti->ti_sum = 0;
 	ti->ti_sum = cksum(m, tlen);
-	((struct ip *)ti)->ip_len = tlen;
 
-	if(flags & TH_RST)
-	  ((struct ip *)ti)->ip_ttl = MAXTTL;
-	else
-	  ((struct ip *)ti)->ip_ttl = IPDEFTTL;
+	struct tcpiphdr tcpiph_save = *(mtod(m, struct tcpiphdr *));
+	m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
+	                                     - sizeof(struct ip);
+	m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
+	                                     - sizeof(struct ip);
+	struct ip *ip = mtod(m, struct ip *);
+	ip->ip_len = tlen;
+	ip->ip_dst = tcpiph_save.ti_dst;
+	ip->ip_src = tcpiph_save.ti_src;
+	ip->ip_p = tcpiph_save.ti_pr;
+
+	if (flags & TH_RST) {
+		ip->ip_ttl = MAXTTL;
+	} else {
+		ip->ip_ttl = IPDEFTTL;
+	}
 
 	(void) ip_output((struct socket *)0, m);
 }
diff --git a/slirp/tcpip.h b/slirp/tcpip.h
index 7974ce3..3c5d127 100644
--- a/slirp/tcpip.h
+++ b/slirp/tcpip.h
@@ -37,15 +37,23 @@
  * Tcp+ip header, after ip options removed.
  */
 struct tcpiphdr {
-	struct 	ipovly ti_i;		/* overlaid ip structure */
-	struct	tcphdr ti_t;		/* tcp header */
+    struct mbuf_ptr ih_mbuf;	/* backpointer to mbuf */
+    union {
+        struct {
+            struct  in_addr ih_src; /* source internet address */
+            struct  in_addr ih_dst; /* destination internet address */
+            uint8_t ih_x1;          /* (unused) */
+            uint8_t ih_pr;          /* protocol */
+        } ti_i4;
+    } ti;
+    uint16_t    ti_x0;
+    uint16_t    ti_len;             /* protocol length */
+    struct      tcphdr ti_t;        /* tcp header */
 };
-#define	ti_mbuf		ti_i.ih_mbuf.mptr
-#define	ti_x1		ti_i.ih_x1
-#define	ti_pr		ti_i.ih_pr
-#define	ti_len		ti_i.ih_len
-#define	ti_src		ti_i.ih_src
-#define	ti_dst		ti_i.ih_dst
+#define	ti_mbuf		ih_mbuf.mptr
+#define	ti_pr		ti.ti_i4.ih_pr
+#define	ti_src		ti.ti_i4.ih_src
+#define	ti_dst		ti.ti_i4.ih_dst
 #define	ti_sport	ti_t.th_sport
 #define	ti_dport	ti_t.th_dport
 #define	ti_seq		ti_t.th_seq
@@ -65,6 +73,13 @@ struct tcpiphdr {
 #define tcpfrag_list_end(F, T) (tcpiphdr2qlink(F) == (struct qlink*)(T))
 #define tcpfrag_list_empty(T) ((T)->seg_next == (struct tcpiphdr*)(T))
 
+/* This is the difference between the size of a tcpiphdr structure, and the
+ * size of actual ip+tcp headers, rounded up since we need to align data.  */
+#define TCPIPHDR_DELTA\
+    (max(0,\
+         (sizeof(struct tcpiphdr)\
+          - sizeof(struct ip) - sizeof(struct tcphdr) + 3) & ~3))
+
 /*
  * Just a clean way to get to the first byte
  * of the packet