Changeset 50013 in vbox

Timestamp:

Dec 31, 2013 2:49:40 AM (11 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

91460

Message:

NAT/ip_icmp.c:

1. ICMP error send in mbuf allocated from mbuf_zone (256b) that reduces maximum size to 214 bytes of payload, but doesn't require allocate additional buffer from cluster zones.
2. composing ICMP error datagram is grouped and commented, the calculation of size of the error ICMP payload delayed to the end of function.

File:

• trunk/src/VBox/Devices/Network/slirp/ip_icmp.c (modified) (4 diffs)

trunk/src/VBox/Devices/Network/slirp/ip_icmp.c

@@ -602 +602 @@
  * ICMP fragmentation is illegal.  All machines must accept 576 bytes in one
  * packet.  The maximum payload is 576-20(ip hdr)-8(icmp hdr)=548
+ * @note: implementation note: MSIZE is 256 bytes (minimal buffer), m_getjcl we allocate two mbufs on: clust_zone 
+ * and mbuf_zone. the maximum payload 256 - 14 (Ethernet header) - 20 (IPv4 hdr) - 8 (ICMPv4 header) = 214
  *
  * @note This function will free msrc!
  */
 
-#define ICMP_MAXDATALEN (IP_MSS-28)
+#define ICMP_MAXDATALEN (MSIZE - 28 - ETH_HLEN)
 void icmp_error(PNATState pData, struct mbuf *msrc, u_char type, u_char code, int minsize, const char *message)
 {
@@ -654 +656 @@
     }
 
-    new_ip_size = sizeof(struct ip) + ICMP_MINLEN + ICMP_MAXDATALEN;
-    new_m_size = if_maxlinkhdr + new_ip_size;
-    if (new_m_size < MSIZE)
-        size = MCLBYTES;
-    else if (new_m_size < MCLBYTES)
-        size = MCLBYTES;
-    else if(new_m_size < MJUM9BYTES)
-        size = MJUM9BYTES;
-    else if (new_m_size < MJUM16BYTES)
-        size = MJUM16BYTES;
-    else
-        AssertMsgFailed(("Unsupported size"));
-    m = m_getjcl(pData, M_NOWAIT, MT_HEADER, M_PKTHDR, size);
+    m = m_gethdr(pData, M_NOWAIT, MT_HEADER);
     if (!m)
         goto end_error;
@@ -673 +663 @@
     m->m_pkthdr.header = mtod(m, void *);
 
-    m->m_len = msrc->m_len < new_ip_size ? msrc->m_len : new_ip_size;
-    memcpy(m->m_data, msrc->m_data, m->m_len);   /* copy msrc to m */
-
-    /* make the header of the reply packet */
-    ip   = mtod(m, struct ip *);
-    hlen = sizeof(struct ip);             /* no options in reply */
+    memcpy(m->m_pkthdr.header, ip, shlen); /* initialize respond IP header with data from original one. */
+
+    ip   = mtod(m, struct ip *); /* ip points to new IP header */
+    hlen = sizeof(struct ip);  /* trim the IP header no options in reply */
 
     /* fill in icmp */
-    m->m_data += hlen;
-    m->m_len  -= hlen;
-
-    icp = mtod(m, struct icmp *);
-
-    if (minsize)
-        s_ip_len = shlen+ICMP_MINLEN;      /* return header+8b only */
-    else if (s_ip_len > ICMP_MAXDATALEN)   /* maximum size */
-        s_ip_len = ICMP_MAXDATALEN;
-
-    m->m_len = ICMP_MINLEN + s_ip_len;     /* 8 bytes ICMP header */
-
-    /* min. size = 8+sizeof(struct ip)+8 */
+    m->m_data += hlen; /* shifts m_data to ICMP header */
+    icp = mtod(m, struct icmp *); /* _icp_: points to the ICMP header */
+    m->m_data += RT_OFFSETOF(struct icmp, icmp_ip); /* shifts m_data to IP header payload */
 
     icp->icmp_type = type;
@@ -700 +678 @@
     icp->icmp_seq = 0;
 
-    memcpy(&icp->icmp_ip, msrc->m_data, s_ip_len);   /* report the ip packet */
-
     HTONS(icp->icmp_ip.ip_len);
     HTONS(icp->icmp_ip.ip_id);
     HTONS(icp->icmp_ip.ip_off);
 
+    memcpy(mtod(m, void *), mtod(msrc, void *), shlen);  /* copy original IP header (with options) */
+    msrc->m_data += shlen; /* _msrc_: shifts m_data of original mbuf to the end of original IP header */
+    msrc->m_len -= shlen; /* _msrc_: alter m_len to size of original IP datagram payload */
+    m->m_data += shlen; /* _m_: shifts m_data to the end of reported IP datagram */
+    /* initialize reported payload of original datagram  with MUST size RFC792 or with rest of allocated mbuf */
+    s_ip_len = minsize ? 8 : M_TRAILINGSPACE(m);
+    /* trims original IP datagram's payload to the lenght of its mbuf size or already reserved space if it's smaller */
+    s_ip_len = RT_MIN(s_ip_len, msrc->m_len);
+    memcpy(mtod(m, void *), mtod(msrc, void *), s_ip_len);
+
 #if DEBUG
     if (message)
     {
-        /* DEBUG : append message to ICMP packet */
+
         size_t message_len;
+        /**
+         * Trim reported payload to first eight bytes (RFC792) to let sniffering tools do
+         * their audit duties, and add hint message to the tail of mandatory piece.
+         */
+        s_ip_len = 8;
+        /**
+         * _m_: shifts m_data to the end of mandatory 8b piece to let M_TRAILINGSPACE
+         * to returns available space with counting mandatory region.
+         */
+        m->m_data += s_ip_len;
         message_len = strlen(message);
-        if (message_len > ICMP_MAXDATALEN)
-            message_len = ICMP_MAXDATALEN;
+        if (message_len > M_TRAILINGSPACE(m))
+            message_len = M_TRAILINGSPACE(m);
+   
+        /**
+         * m->m_data points to the end of 8 bytes payload, and m->m_len is length of appended 
+         * message.
+         */
         m_append(pData, m, (int)message_len, message);
+        m->m_data -= s_ip_len; /* now we're ready for further processing, with pointing to mandatory payload */
     }
 #else
     NOREF(message);
 #endif
-
+    
+    m->m_data -= shlen + RT_OFFSETOF(struct icmp, icmp_ip); /* _m_: shifts m_data to the start of ICMP header */
+    m->m_len += s_ip_len + shlen + RT_OFFSETOF(struct icmp, icmp_ip); /* _m_: m_len counts bytes in IP payload */
+    
     icp->icmp_cksum = 0;
     icp->icmp_cksum = cksum(m, m->m_len);