Fix another fuzzer bug.

ChangeLog

@@ -53,6 +53,12 @@ LLVM fuzzer.
 14. Fix infinite recursion in the JIT compiler when certain patterns such as
 /(?:|a|){100}x/ are analysed.
 
+15. Some patterns with character classes involving [: and \\ were incorrectly
+compiled and could cause reading from uninitialized memory or an incorrect
+error diagnosis. Examples are: /[[:\\](?<[::]/ and /[[:\\](?'abc')[a:]. The
+first of these bugs was discovered by Karl Skomski with the LLVM fuzzer.
+
+
 
 Version 10.20 30-June-2015
 --------------------------

src/pcre2_compile.c

@@ -2574,11 +2574,11 @@ didn't consider this to be a POSIX class. Likewise for [:1234:].
 The problem in trying to be exactly like Perl is in the handling of escapes. We
 have to be sure that [abc[:x\]pqr] is *not* treated as containing a POSIX
 class, but [abc[:x\]pqr:]] is (so that an error can be generated). The code
-below handles the special case of \], but does not try to do any other escape
-processing. This makes it different from Perl for cases such as [:l\ower:]
-where Perl recognizes it as the POSIX class "lower" but PCRE does not recognize
-"l\ower". This is a lesser evil than not diagnosing bad classes when Perl does,
-I think.
+below handles the special cases \\ and \], but does not try to do any other
+escape processing. This makes it different from Perl for cases such as
+[:l\ower:] where Perl recognizes it as the POSIX class "lower" but PCRE does
+not recognize "l\ower". This is a lesser evil than not diagnosing bad classes
+when Perl does, I think.
 
 A user pointed out that PCRE was rejecting [:a[:digit:]] whereas Perl was not.
 It seems that the appearance of a nested POSIX class supersedes an apparent
@@ -2606,7 +2606,9 @@ terminator = *(++ptr);   /* compiler warns about "non-constant" initializer. */
 
 for (++ptr; *ptr != CHAR_NULL; ptr++)
   {
-  if (*ptr == CHAR_BACKSLASH && ptr[1] == CHAR_RIGHT_SQUARE_BRACKET) ptr++;
+  if (*ptr == CHAR_BACKSLASH &&
+      (ptr[1] == CHAR_RIGHT_SQUARE_BRACKET || ptr[1] == CHAR_BACKSLASH))
+    ptr++;
   else if (*ptr == CHAR_RIGHT_SQUARE_BRACKET) return FALSE;
   else
     {
@@ -3117,6 +3119,8 @@ for (; ptr < cb->end_pattern; ptr++)
 
     for (;;)
       {
+      PCRE2_SPTR tempptr;
+
       if (c == CHAR_NULL && ptr >= cb->end_pattern)
         {
         errorcode = ERR6;  /* Missing terminating ']' */
@@ -3143,12 +3147,11 @@ for (; ptr < cb->end_pattern; ptr++)
         }
 
       /* Skip POSIX class names. */
-
       if (c == CHAR_LEFT_SQUARE_BRACKET &&
           (ptr[1] == CHAR_COLON || ptr[1] == CHAR_DOT ||
-           ptr[1] == CHAR_EQUALS_SIGN) && check_posix_syntax(ptr, &ptr))
+           ptr[1] == CHAR_EQUALS_SIGN) && check_posix_syntax(ptr, &tempptr))
         {
-        ptr++;
+        ptr = tempptr + 1;
         }
       else if (c == CHAR_BACKSLASH)
         {

testdata/testinput2

@@ -4346,4 +4346,8 @@ a random value. /Ix
 
 /((?x)(?#))#(?'abc')/I
 
+/[[:\\](?<[::]/
+
+/[[:\\](?'abc')[a:]/I
+
 # End of testinput2 

testdata/testoutput2

@@ -14524,4 +14524,14 @@ Named capturing subpatterns:
 First code unit = '#'
 Subject length lower bound = 1
 
+/[[:\\](?<[::]/
+Failed: error 124 at offset 9: unrecognized character after (?<
+
+/[[:\\](?'abc')[a:]/I
+Capturing subpattern count = 1
+Named capturing subpatterns:
+  abc   1
+Starting code units: : [ \ 
+Subject length lower bound = 2
+
 # End of testinput2