pcre2_compile: avoid 1 byte buffer overread parsing VERBs (#487)

As reported recently by ef218fb (Guard against out-of-bounds memory
access when parsing LIMIT_HEAP et al (#463), 2024-09-07), a malformed
pattern could result in reading 1 byte past its end.

Fix a similar issue that affects all VERBs and add test cases to
ensure the original bug and all its siblings are no longer an issue.

While at it fix the wording of the related documentation.

ChangeLog

@@ -82,21 +82,23 @@ pattern.
 14. Item 43 of 10.43 was incomplete because it addressed only \z and not \Z,
 which was still misbehaving when matching fragments inside invalid UTF strings.
 
-15. Octal escapes of the form \045 or \111 were not being recognized in 
+15. Octal escapes of the form \045 or \111 were not being recognized in
 substitution strings, and if encountered gave an error, though the \o{...} form
 was recognized. This bug is now fixed.
 
-16. Merged PR475, which implements title casing in substitution strings a la 
+16. Merged PR475, which implements title casing in substitution strings a la
 Perl.
 
 17. Merged PR478, which disallows \x if not followed by { or a hex digit.
 
 18. Merged PR473, which implements Python-style backrefs in substitutions.
 
-19. Merged PR483, which adding \g<n> and $<name> to replacement strings.
+19. Merged PR483, which is adding \g<n> and $<name> to replacement strings.
 
 20. Merged PR470, which adds PCRE2_EXTRA_NO_BS0 and PCRE2_EXTRA_PYTHON_OCTAL.
 
+21. Prevent 1 byte overread when parsing malformed patterns with early VERBs.
+
 
 Version 10.44 07-June-2024
 --------------------------

doc/pcre2syntax.3

@@ -408,8 +408,8 @@ only one hyphen. Setting (but no unsetting) is allowed after (?^ for example
 example (?i:...).
 .P
 The following are recognized only at the very start of a pattern or after one
-of the newline or \eR options with similar syntax. More than one of them may
-appear. For the first three, d is a decimal number.
+of the newline or \eR sequences or options with similar syntax. More than one
+of them may appear. For the first three, d is a decimal number.
 .sp
   (*LIMIT_DEPTH=d) set the backtracking limit to d
   (*LIMIT_HEAP=d)  set the heap size limit to d * 1024 bytes

src/pcre2_compile.c

@@ -10404,12 +10404,13 @@ if ((options & PCRE2_LITERAL) == 0)
     {
     for (i = 0; i < sizeof(pso_list)/sizeof(pso); i++)
       {
-      uint32_t c, pp;
       const pso *p = pso_list + i;
 
       if (patlen - skipatstart - 2 >= p->length &&
           PRIV(strncmp_c8)(ptr + skipatstart + 2, p->name, p->length) == 0)
         {
+        uint32_t c, pp;
+
         skipatstart += p->length + 2;
         switch(p->type)
           {
@@ -10436,18 +10437,12 @@ if ((options & PCRE2_LITERAL) == 0)
           case PSO_LIMH:
           c = 0;
           pp = skipatstart;
-          if (!IS_DIGIT(ptr[pp]))
-            {
-            errorcode = ERR60;
-            ptr += pp;
-            goto HAD_EARLY_ERROR;
-            }
           while (pp < patlen && IS_DIGIT(ptr[pp]))
             {
             if (c > UINT32_MAX / 10 - 1) break;   /* Integer overflow */
             c = c*10 + (ptr[pp++] - CHAR_0);
             }
-          if (pp >= patlen || ptr[pp] != CHAR_RIGHT_PARENTHESIS)
+          if (pp >= patlen || pp == skipatstart || ptr[pp] != CHAR_RIGHT_PARENTHESIS)
             {
             errorcode = ERR60;
             ptr += pp;

testdata/testinput2

@@ -5261,6 +5261,14 @@ a)"xI
 
 /(*LIMIT_HEAP=0)xxx/I
 
+/(*LIMIT_HEAP=123/use_length
+
+/(*LIMIT_MATCH=/use_length
+
+/(*CRLF)(*LIMIT_DEPTH=/use_length
+
+/(*CRLF)(*LIMIT_RECURSION=1)(*BOGUS/use_length
+
 /\d{0,3}(*:abc)(?C1)xxx/callout_info
 
 # ----------------------------------------------------------------------

testdata/testoutput2

@@ -16220,6 +16220,18 @@ First code unit = 'x'
 Last code unit = 'x'
 Subject length lower bound = 3
 
+/(*LIMIT_HEAP=123/use_length
+Failed: error 160 at offset 16: (*VERB) not recognized or malformed
+
+/(*LIMIT_MATCH=/use_length
+Failed: error 160 at offset 14: (*VERB) not recognized or malformed
+
+/(*CRLF)(*LIMIT_DEPTH=/use_length
+Failed: error 160 at offset 21: (*VERB) not recognized or malformed
+
+/(*CRLF)(*LIMIT_RECURSION=1)(*BOGUS/use_length
+Failed: error 160 at offset 34: (*VERB) not recognized or malformed
+
 /\d{0,3}(*:abc)(?C1)xxx/callout_info
 Callout 1  x