X-Git-Url: https://git.tcpdump.org/tcpdump/blobdiff_plain/db7a7633e65ea66dacb40450d375c00d3f305408..d2777156522f139a858bd6b5b51e364826bc95a7:/netdissect.c

diff --git a/netdissect.c b/netdissect.c
index 4d4a4a59..000d1ffc 100644
--- a/netdissect.c
+++ b/netdissect.c
@@ -123,14 +123,14 @@ nd_load_smi_module(const char *module, char *errbuf, size_t errbuf_size)
 {
 #ifdef USE_LIBSMI
 	if (smiLoadModule(module) == 0) {
-		nd_snprintf(errbuf, errbuf_size, "could not load MIB module %s",
+		snprintf(errbuf, errbuf_size, "could not load MIB module %s",
 		    module);
 		return (-1);
 	}
 	nd_smi_module_loaded = 1;
 	return (0);
 #else
-	nd_snprintf(errbuf, errbuf_size, "MIB module %s not loaded: no libsmi support",
+	snprintf(errbuf, errbuf_size, "MIB module %s not loaded: no libsmi support",
 	    module);
 	return (-1);
 #endif
@@ -149,7 +149,7 @@ nd_smi_version_string(void)
 
 int
 nd_push_buffer(netdissect_options *ndo, u_char *new_buffer,
-    const u_char *new_packetp, const u_char *new_snapend)
+	       const u_char *new_packetp, const u_int newlen)
 {
 	struct netdissect_saved_packet_info *ndspi;
 
@@ -162,20 +162,30 @@ nd_push_buffer(netdissect_options *ndo, u_char *new_buffer,
 	ndspi->ndspi_prev = ndo->ndo_packet_info_stack;
 
 	ndo->ndo_packetp = new_packetp;
-	ndo->ndo_snapend = new_snapend;
+	ndo->ndo_snapend = new_packetp + newlen;
 	ndo->ndo_packet_info_stack = ndspi;
 
 	return (1);	/* success */
 }
 
+
 /*
- * Set a new snapshot end to the minimum of the existing snapshot end
- * and the new snapshot end.
+ * In a given netdissect_options structure:
+ *
+ *    push the current packet information onto the packet information
+ *    stack;
+ *
+ *    given a pointer into the packet and a length past that point in
+ *    the packet, calculate a new snapshot end that's at the lower
+ *    of the current snapshot end and that point in the packet;
+ *
+ *    set the snapshot end to that new value.
  */
 int
-nd_push_snapend(netdissect_options *ndo, const u_char *new_snapend)
+nd_push_snaplen(netdissect_options *ndo, const u_char *bp, const u_int newlen)
 {
 	struct netdissect_saved_packet_info *ndspi;
+	u_int snaplen_remaining;
 
 	ndspi = (struct netdissect_saved_packet_info *)malloc(sizeof(struct netdissect_saved_packet_info));
 	if (ndspi == NULL)
@@ -185,32 +195,87 @@ nd_push_snapend(netdissect_options *ndo, const u_char *new_snapend)
 	ndspi->ndspi_snapend = ndo->ndo_snapend;
 	ndspi->ndspi_prev = ndo->ndo_packet_info_stack;
 
-	/* No new packet pointer, either */
-	if (new_snapend < ndo->ndo_snapend)
-		ndo->ndo_snapend = new_snapend;
+	/*
+	 * Push the saved previous data onto the stack.
+	 */
 	ndo->ndo_packet_info_stack = ndspi;
 
+	/*
+	 * Find out how many bytes remain after the current snapend.
+	 *
+	 * We're restricted to packets with at most UINT_MAX bytes;
+	 * cast the result to u_int, so that we don't get truncation
+	 * warnings on LP64 and LLP64 platforms.  (ptrdiff_t is
+	 * signed and we want an unsigned difference; the pointer
+	 * should at most be equal to snapend, and must *never*
+	 * be past snapend.)
+	 */
+	snaplen_remaining = (u_int)(ndo->ndo_snapend - bp);
+
+	/*
+	 * If the new snapend is smaller than the one calculated
+	 * above, set the snapend to that value, otherwise leave
+	 * it unchanged.
+	 */
+	if (newlen <= snaplen_remaining) {
+		/* Snapend isn't past the previous snapend */
+		ndo->ndo_snapend = bp + newlen;
+	}
+
 	return (1);	/* success */
 }
 
 /*
- * Change an already-pushed snapshot end.  This may increase the
+ * In a given netdissect_options structure:
+ *
+ *    given a pointer into the packet and a length past that point in
+ *    the packet, calculate a new snapshot end that's at the lower
+ *    of the previous snapshot end - or, if there is no previous
+ *    snapshot end, the current snapshot end - and that point in the
+ *    packet;
+ *
+ *    set the snapshot end to that new value.
+ *
+ * This is to change the current snapshot end.  This may increase the
  * snapshot end, as it may be used, for example, for a Jumbo Payload
  * option in IPv6.  It must not increase it past the snapshot length
  * atop which the current one was pushed, however.
  */
 void
-nd_change_snapend(netdissect_options *ndo, const u_char *new_snapend)
+nd_change_snaplen(netdissect_options *ndo, const u_char *bp, const u_int newlen)
 {
 	struct netdissect_saved_packet_info *ndspi;
+	const u_char *previous_snapend;
+	u_int snaplen_remaining;
 
 	ndspi = ndo->ndo_packet_info_stack;
-	if (ndspi->ndspi_prev != NULL) {
-		if (new_snapend <= ndspi->ndspi_prev->ndspi_snapend)
-			ndo->ndo_snapend = new_snapend;
-	} else {
-		if (new_snapend < ndo->ndo_snapend)
-			ndo->ndo_snapend = new_snapend;
+	if (ndspi->ndspi_prev != NULL)
+		previous_snapend = ndspi->ndspi_prev->ndspi_snapend;
+	else
+		previous_snapend = ndo->ndo_snapend;
+
+	/*
+	 * Find out how many bytes remain after the previous
+	 * snapend - or, if there is no previous snapend, after
+	 * the current snapend.
+	 *
+	 * We're restricted to packets with at most UINT_MAX bytes;
+	 * cast the result to u_int, so that we don't get truncation
+	 * warnings on LP64 and LLP64 platforms.  (ptrdiff_t is
+	 * signed and we want an unsigned difference; the pointer
+	 * should at most be equal to snapend, and must *never*
+	 * be past snapend.)
+	 */
+	snaplen_remaining = (u_int)(previous_snapend - bp);
+
+	/*
+	 * If the new snapend is smaller than the one calculated
+	 * above, set the snapend to that value, otherwise leave
+	 * it unchanged.
+	 */
+	if (newlen <= snaplen_remaining) {
+		/* Snapend isn't past the previous snapend */
+		ndo->ndo_snapend = bp + newlen;
 	}
 }