Add recursion limit to auto-possessification code.

ChangeLog

@@ -25,6 +25,11 @@ when this assertion was used as a condition, for example (?(?!)a|b). In
 pcre2_match() it worked by luck; in pcre2_dfa_match() it gave an incorrect
 error about an unsupported item.
 
+8. For some types of pattern, for example /Z*(|d*){216}/, the auto-
+possessification code could take exponential time to complete. A recursion 
+depth limit of 10000 has been imposed to limit the resources used by this 
+optimization. This infelicity was discovered by the LLVM fuzzer.
+
 
 Version 10.10 06-March-2015
 ---------------------------

src/pcre2_auto_possess.c

@@ -561,13 +561,15 @@ Arguments:
   utf         TRUE in UTF mode
   cb          compile data block
   base_list   the data list of the base opcode
+  base_end    the end of the data list
+  rec_limit   points to recursion depth counter  
 
 Returns:      TRUE if the auto-possessification is possible
 */
 
 static BOOL
 compare_opcodes(PCRE2_SPTR code, BOOL utf, const compile_block *cb,
-  const uint32_t *base_list, PCRE2_SPTR base_end)
+  const uint32_t *base_list, PCRE2_SPTR base_end, int *rec_limit)
 {
 PCRE2_UCHAR c;
 uint32_t list[8];
@@ -584,6 +586,8 @@ uint32_t chr;
 BOOL accepted, invert_bits;
 BOOL entered_a_group = FALSE;
 
+if (--(*rec_limit) <= 0) return FALSE;  /* Recursion has gone too deep */
+
 /* Note: the base_list[1] contains whether the current opcode has a greedy
 (represented by a non-zero value) quantifier. This is a different from
 other character type lists, which store here that the character iterator
@@ -660,7 +664,8 @@ for(;;)
 
     while (*next_code == OP_ALT)
       {
-      if (!compare_opcodes(code, utf, cb, base_list, base_end)) return FALSE;
+      if (!compare_opcodes(code, utf, cb, base_list, base_end, rec_limit)) 
+        return FALSE;
       code = next_code + 1 + LINK_SIZE;
       next_code += GET(next_code, 1);
       }
@@ -680,7 +685,7 @@ for(;;)
     /* The bracket content will be checked by the OP_BRA/OP_CBRA case above. */
 
     next_code += 1 + LINK_SIZE;
-    if (!compare_opcodes(next_code, utf, cb, base_list, base_end))
+    if (!compare_opcodes(next_code, utf, cb, base_list, base_end, rec_limit))
       return FALSE;
 
     code += PRIV(OP_lengths)[c];
@@ -1116,6 +1121,7 @@ register PCRE2_UCHAR c;
 PCRE2_SPTR end;
 PCRE2_UCHAR *repeat_opcode;
 uint32_t list[8];
+int rec_limit;
 
 for (;;)
   {
@@ -1130,7 +1136,8 @@ for (;;)
       get_chr_property_list(code, utf, cb->fcc, list) : NULL;
     list[1] = c == OP_STAR || c == OP_PLUS || c == OP_QUERY || c == OP_UPTO;
 
-    if (end != NULL && compare_opcodes(end, utf, cb, list, end))
+    rec_limit = 10000;
+    if (end != NULL && compare_opcodes(end, utf, cb, list, end, &rec_limit))
       {
       switch(c)
         {
@@ -1186,7 +1193,8 @@ for (;;)
 
       list[1] = (c & 1) == 0;
 
-      if (compare_opcodes(end, utf, cb, list, end))
+      rec_limit = 10000;
+      if (compare_opcodes(end, utf, cb, list, end, &rec_limit))
         {
         switch (c)
           {

testdata/testinput1

@@ -5710,4 +5710,6 @@ name)/mark
 
 /(\2)(\1)/
 
+"Z*(|d*){216}"
+
 # End of testinput1 

testdata/testoutput1

@@ -9420,4 +9420,6 @@ No match
 
 /(\2)(\1)/
 
+"Z*(|d*){216}"
+
 # End of testinput1