CVE-2017-13045/VQP: add some bounds checks

[tcpdump] / print-domain.c

diff --git a/print-domain.c b/print-domain.c
index c3066f7d7d30e75a7ce05ccb0e7feedd768b67bd..9a2b9e85687b633fcb4564ff299cd85f738c358e 100644 (file)
--- a/print-domain.c
+++ b/print-domain.c
@@ -19,6 +19,8 @@
  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+/* \summary: Domain Name System (DNS) printer */
+
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif
@@ -149,15 +151,14 @@ ns_nprint(netdissect_options *ndo,
        register u_int i, l;
        register const u_char *rp = NULL;
        register int compress = 0;
-       int chars_processed;
        int elt;
-       int data_size = ndo->ndo_snapend - bp;
+       u_int offset, max_offset;
 
        if ((l = labellen(ndo, cp)) == (u_int)-1)
                return(NULL);
        if (!ND_TTEST2(*cp, 1))
                return(NULL);
-       chars_processed = 1;
+       max_offset = (u_int)(cp - bp);
        if (((i = *cp++) & INDIR_MASK) != INDIR_MASK) {
                compress = 0;
                rp = cp + l;
@@ -172,24 +173,28 @@ ns_nprint(netdissect_options *ndo,
                                }
                                if (!ND_TTEST2(*cp, 1))
                                        return(NULL);
-                               cp = bp + (((i << 8) | *cp) & 0x3fff);
+                               offset = (((i << 8) | *cp) & 0x3fff);
+                               /*
+                                * This must move backwards in the packet.
+                                * No RFC explicitly says that, but BIND's
+                                * name decompression code requires it,
+                                * as a way of preventing infinite loops
+                                * and other bad behavior, and it's probably
+                                * what was intended (compress by pointing
+                                * to domain name suffixes already seen in
+                                * the packet).
+                                */
+                               if (offset >= max_offset) {
+                                       ND_PRINT((ndo, "<BAD PTR>"));
+                                       return(NULL);
+                               }
+                               max_offset = offset;
+                               cp = bp + offset;
                                if ((l = labellen(ndo, cp)) == (u_int)-1)
                                        return(NULL);
                                if (!ND_TTEST2(*cp, 1))
                                        return(NULL);
                                i = *cp++;
-                               chars_processed++;
-
-                               /*
-                                * If we've looked at every character in
-                                * the message, this pointer will make
-                                * us look at some character again,
-                                * which means we're looping.
-                                */
-                               if (chars_processed >= data_size) {
-                                       ND_PRINT((ndo, "<LOOP>"));
-                                       return (NULL);
-                               }
                                continue;
                        }
                        if ((i & INDIR_MASK) == EDNS0_MASK) {
@@ -210,14 +215,12 @@ ns_nprint(netdissect_options *ndo,
                        }
 
                        cp += l;
-                       chars_processed += l;
                        ND_PRINT((ndo, "."));
                        if ((l = labellen(ndo, cp)) == (u_int)-1)
                                return(NULL);
                        if (!ND_TTEST2(*cp, 1))
                                return(NULL);
                        i = *cp++;
-                       chars_processed++;
                        if (!compress)
                                rp += l + 1;
                }
@@ -395,7 +398,7 @@ ns_rprint(netdissect_options *ndo,
        } else if (ndo->ndo_vflag > 2) {
                /* print ttl */
                ND_PRINT((ndo, " ["));
-               relts_print(ndo, EXTRACT_32BITS(cp));
+               unsigned_relts_print(ndo, EXTRACT_32BITS(cp));
                ND_PRINT((ndo, "]"));
                cp += 4;
        } else {