kbx: Add bounds check to detect corrupt keyboxes.

* kbx/keybox-dump.c (_keybox_dump_blob): Fix the fixmes.
--

kbxutil is a debug tool but nevertheless it should behave well and not
read beyond allocated buffers and in turn crash.

Vincent Ulitzsch and Dominik Maier were kind enough to report these
crashes along with a couple of test keyboxes and crash analysis.

Signed-off-by: Werner Koch <wk@gnupg.org>

kbx/keybox-dump.c

@@ -84,6 +84,7 @@ print_checksum (const byte *buffer, size_t length, size_t unhashed, FILE *fp)
     }
   else
     hashlen = 20;
+
   if (length < 5+unhashed)
     {
       fputs ("[blob too short for a checksum]\n", fp);
@@ -170,6 +171,7 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
   ulong nserial;
   ulong unhashed;
   const byte *p;
+  const byte *pend;
   int is_fpr32;  /* blob version 2 */
 
   buffer = _keybox_get_blob_image (blob, &length);
@@ -250,7 +252,18 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
       || rawdata_off+rawdata_len > length
       || rawdata_len + 4 > length
       || rawdata_off+rawdata_len + 4 > length)
-    fprintf (fp, "[Error: raw data larger than blob]\n");
+    {
+      fprintf (fp, "[Error: raw data larger than blob]\n");
+      return -1;
+    }
+
+  if (rawdata_off > length
+      || rawdata_len > length
+      || rawdata_off + rawdata_len > length)
+    {
+      fprintf (fp, "[Error: unhashed data larger than blob]\n");
+      return -1;
+    }
   unhashed = length - rawdata_off - rawdata_len;
   fprintf (fp, "Unhashed: %lu\n", unhashed);
 
@@ -263,35 +276,66 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
 
   keyinfolen = get16 (buffer + 18 );
   fprintf (fp, "Key-Info-Length: %lu\n", keyinfolen);
-  /* fixme: check bounds */
   p = buffer + 20;
+  pend = buffer + length;
   for (n=0; n < nkeys; n++, p += keyinfolen)
     {
       ulong kidoff, kflags;
 
+      if (p + keyinfolen >= pend)
+        {
+          fprintf (fp, "[Error: key data larger than blob]\n");
+          return -1;
+        }
+
       fprintf (fp, "Key-Fpr[%lu]: ", n );
       if (is_fpr32)
         {
+          if (p + 32 + 2 >= pend)
+            {
+              fprintf (fp, "[Error: fingerprint data larger than blob]\n");
+              return -1;
+            }
           kflags = get16 (p + 32 );
           for (i=0; i < ((kflags & 0x80)?32:20); i++ )
             fprintf (fp, "%02X", p[i]);
         }
       else
         {
+          if (p + 20 + 4 >= pend)
+            {
+              fprintf (fp, "[Error: fingerprint data larger than blob]\n");
+              return -1;
+            }
           for (i=0; i < 20; i++ )
             fprintf (fp, "%02X", p[i]);
           kidoff = get32 (p + 20);
           fprintf (fp, "\nKey-Kid-Off[%lu]: %lu\n", n, kidoff );
           fprintf (fp, "Key-Kid[%lu]: ", n );
-          /* fixme: check bounds */
+
+          if (p + kidoff + 8 >= pend)
+            {
+              fprintf (fp, "[Error: fingerprint data larger than blob]\n");
+              return -1;
+            }
           for (i=0; i < 8; i++ )
             fprintf (fp, "%02X", buffer[kidoff+i] );
-          kflags = get16 (p + 24 );
+          if (p + 24 >= pend)
+            {
+              fprintf (fp, "[Error: fingerprint data larger than blob]\n");
+              return -1;
+            }
+          kflags = get16 (p + 24);
         }
       fprintf( fp, "\nKey-Flags[%lu]: %04lX\n", n, kflags);
     }
 
   /* serial number */
+  if (p + 2 >= pend)
+    {
+      fprintf (fp, "[Error: data larger than blob]\n");
+      return -1;
+    }
   fputs ("Serial-No: ", fp);
   nserial = get16 (p);
   p += 2;
@@ -299,22 +343,37 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
     fputs ("none", fp);
   else
     {
+      if (p + nserial >= pend)
+        {
+          fprintf (fp, "[Error: data larger than blob]\n");
+          return -1;
+        }
       for (; nserial; nserial--, p++)
         fprintf (fp, "%02X", *p);
     }
   putc ('\n', fp);
 
   /* user IDs */
+  if (p + 4 >= pend)
+    {
+      fprintf (fp, "[Error: data larger than blob]\n");
+      return -1;
+    }
   nuids = get16 (p);
   fprintf (fp, "Uid-Count: %lu\n", nuids );
   uidinfolen = get16  (p + 2);
   fprintf (fp, "Uid-Info-Length: %lu\n", uidinfolen);
-  /* fixme: check bounds */
   p += 4;
   for (n=0; n < nuids; n++, p += uidinfolen)
     {
       ulong uidoff, uidlen, uflags;
 
+      if (p + uidinfolen >= pend || uidinfolen < 8)
+        {
+          fprintf (fp, "[Error: data larger than blob]\n");
+          return -1;
+        }
+
       uidoff = get32( p );
       uidlen = get32( p+4 );
       if (type == KEYBOX_BLOBTYPE_X509 && !n)
@@ -335,8 +394,21 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
           fprintf (fp, "Uid-Len[%lu]: %lu\n", n, uidlen );
           fprintf (fp, "Uid[%lu]: \"", n );
         }
+
+      if (uidoff + uidlen > length
+          || uidoff + uidlen < uidoff
+          || uidoff + uidlen < uidlen)
+        {
+          fprintf (fp, "[Error: data larger than blob]\n");
+          return -1;
+        }
       print_string (fp, buffer+uidoff, uidlen, '\"');
       fputs ("\"\n", fp);
+      if (p + 8 + 2 + 1 >= pend)
+        {
+          fprintf (fp, "[Error: data larger than blob]\n");
+          return -1;
+        }
       uflags = get16 (p + 8);
       if (type == KEYBOX_BLOBTYPE_X509 && !n)
         {
@@ -355,11 +427,15 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
         }
     }
 
+  if (p + 2 + 2 >= pend)
+    {
+      fprintf (fp, "[Error: data larger than blob]\n");
+      return -1;
+    }
   nsigs = get16 (p);
   fprintf (fp, "Sig-Count: %lu\n", nsigs );
   siginfolen = get16 (p + 2);
   fprintf (fp, "Sig-Info-Length: %lu\n", siginfolen );
-  /* fixme: check bounds  */
   p += 4;
   {
     int in_range = 0;
@@ -369,6 +445,11 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
       {
         ulong sflags;
 
+        if (p + siginfolen >= pend || siginfolen < 4)
+          {
+            fprintf (fp, "[Error: data larger than blob]\n");
+            return -1;
+          }
         sflags = get32 (p);
         if (!in_range && !sflags)
           {
@@ -402,6 +483,12 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
     if (in_range)
       fprintf (fp, "Sig-Expire[%lu-%lu]: [not checked]\n", first, n-1);
   }
+
+  if (p + 16 >= pend)
+    {
+      fprintf (fp, "[Error: data larger than blob]\n");
+      return -1;
+    }
   fprintf (fp, "Ownertrust: %d\n", p[0] );
   fprintf (fp, "All-Validity: %d\n", p[1] );
   p += 4;
@@ -414,6 +501,12 @@ _keybox_dump_blob (KEYBOXBLOB blob, FILE *fp)
   n = get32 (p );
   p += 4;
   fprintf (fp, "Created-At: %lu\n", n );
+
+  if (p + 4 >= pend)
+    {
+      fprintf (fp, "[Error: data larger than blob]\n");
+      return -1;
+    }
   n = get32 (p );
   fprintf (fp, "Reserved-Space: %lu\n", n );