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, 105 insertions, 43 deletions

diff --git a/if.h b/if.h
index 6ee566d..44e4774 100644
--- a/if.h
+++ b/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/mbuf.c b/mbuf.c
index bdda609..cfaa92c 100644
--- a/mbuf.c
+++ b/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.c b/slirp.c
index c5037e3..65b4a22 100644
--- a/slirp.c
+++ b/slirp.c
@@ -760,15 +760,16 @@ 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/socket.c b/socket.c
index dcc2f05..48d8893 100644
--- a/socket.c
+++ b/socket.c
@@ -492,7 +492,18 @@ void 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/tcp_input.c b/tcp_input.c
index 4ad3f8b..3b02559 100644
--- a/tcp_input.c
+++ b/tcp_input.c
@@ -256,11 +256,6 @@ void 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 @@ void 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;
+    tlen = ip->ip_len;
     tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
-    memset(&ti->ti_i.ih_mbuf, 0, sizeof(struct mbuf_ptr));
-    ti->ti_x1 = 0;
+    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;
     }
@@ -602,6 +611,10 @@ findso:
                     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));
             }
@@ -1457,7 +1470,7 @@ int 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/tcp_output.c b/tcp_output.c
index cbe4fa6..808df35 100644
--- a/tcp_output.c
+++ b/tcp_output.c
@@ -444,14 +444,23 @@ send:
      */
     m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
 
-    {
-        ((struct ip *)ti)->ip_len = m->m_len;
+    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_ttl = IPDEFTTL;
-        ((struct ip *)ti)->ip_tos = so->so_iptos;
+    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;
+
+    ip->ip_ttl = IPDEFTTL;
+    ip->ip_tos = so->so_iptos;
+
+    error = ip_output(so, m);
 
-        error = ip_output(so, m);
-    }
     if (error) {
     out:
         return (error);
diff --git a/tcp_subr.c b/tcp_subr.c
index 5d1d3be..8a4a6e7 100644
--- a/tcp_subr.c
+++ b/tcp_subr.c
@@ -74,9 +74,10 @@ void 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;
@@ -128,6 +129,7 @@ void 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 {
         /*
@@ -154,7 +156,7 @@ void tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
     m->m_len = tlen;
 
     ti->ti_mbuf = NULL;
-    ti->ti_x1 = 0;
+    ti->ti_x0 = 0;
     ti->ti_seq = htonl(seq);
     ti->ti_ack = htonl(ack);
     ti->ti_x2 = 0;
@@ -167,12 +169,23 @@ void 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/tcpip.h b/tcpip.h
index 6c88289..edc4ed1 100644
--- a/tcpip.h
+++ b/tcpip.h
@@ -37,15 +37,23 @@
  * Tcp+ip header, after ip options removed.
  */
 struct tcpiphdr {
-    struct ipovly ti_i; /* overlaid ip structure */
+    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
@@ -67,6 +75,13 @@ 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