Fix other cases where backtracking after \C could cause a crash.

ChangeLog

@@ -76,7 +76,8 @@ the code there did catch the loop.
 19. If a greedy quantified \X was preceded by \C in UTF mode (e.g. \C\X*), 
 and a subsequent item in the pattern caused a non-match, backtracking over the
 repeated \X did not stop, but carried on past the start of the subject, causing
-reference to random memory and/or a segfault.  This bug was discovered by the
+reference to random memory and/or a segfault. There were also some other cases
+where backtracking after \C could crash. This set of bugs was discovered by the
 LLVM fuzzer.
 
 

src/pcre2_match.c

@@ -3576,9 +3576,13 @@ for (;;)
             }
 
           if (possessive) continue;    /* No backtracking */
+
+          /* After \C in UTF mode, pp might be in the middle of a Unicode
+          character. Use <= pp to ensure backtracking doesn't go too far. */
+
           for(;;)
             {
-            if (eptr == pp) goto TAIL_RECURSE;
+            if (eptr <= pp) goto TAIL_RECURSE;
             RMATCH(eptr, ecode, offset_top, mb, eptrb, RM23);
             if (rrc != MATCH_NOMATCH) RRETURN(rrc);
             eptr--;
@@ -3973,9 +3977,13 @@ for (;;)
             eptr += len;
             }
           if (possessive) continue;    /* No backtracking */
+
+          /* After \C in UTF mode, pp might be in the middle of a Unicode
+          character. Use <= pp to ensure backtracking doesn't go too far. */
+
           for(;;)
             {
-            if (eptr == pp) goto TAIL_RECURSE;
+            if (eptr <= pp) goto TAIL_RECURSE;
             RMATCH(eptr, ecode, offset_top, mb, eptrb, RM30);
             if (rrc != MATCH_NOMATCH) RRETURN(rrc);
             eptr--;
@@ -4108,9 +4116,13 @@ for (;;)
             eptr += len;
             }
           if (possessive) continue;    /* No backtracking */
+
+          /* After \C in UTF mode, pp might be in the middle of a Unicode
+          character. Use <= pp to ensure backtracking doesn't go too far. */
+
           for(;;)
             {
-            if (eptr == pp) goto TAIL_RECURSE;
+            if (eptr <= pp) goto TAIL_RECURSE;
             RMATCH(eptr, ecode, offset_top, mb, eptrb, RM34);
             if (rrc != MATCH_NOMATCH) RRETURN(rrc);
             eptr--;
@@ -5679,9 +5691,13 @@ for (;;)
         /* eptr is now past the end of the maximum run */
 
         if (possessive) continue;    /* No backtracking */
+
+        /* After \C in UTF mode, pp might be in the middle of a Unicode
+        character. Use <= pp to ensure backtracking doesn't go too far. */
+
         for(;;)
           {
-          if (eptr == pp) goto TAIL_RECURSE;
+          if (eptr <= pp) goto TAIL_RECURSE;
           RMATCH(eptr, ecode, offset_top, mb, eptrb, RM44);
           if (rrc != MATCH_NOMATCH) RRETURN(rrc);
           eptr--;
@@ -5999,9 +6015,13 @@ for (;;)
           }
 
         if (possessive) continue;    /* No backtracking */
+
+        /* After \C in UTF mode, pp might be in the middle of a Unicode
+        character. Use <= pp to ensure backtracking doesn't go too far. */
+
         for(;;)
           {
-          if (eptr == pp) goto TAIL_RECURSE;
+          if (eptr <= pp) goto TAIL_RECURSE;
           RMATCH(eptr, ecode, offset_top, mb, eptrb, RM46);
           if (rrc != MATCH_NOMATCH) RRETURN(rrc);
           eptr--;

testdata/testinput4

@@ -2226,4 +2226,7 @@
 /utf
     Ӆ\x0a
 
+/\C(\W?ſ)'?{{/utf
+    \\C(\\W?ſ)'?{{
+
 # End of testinput4

testdata/testoutput4

@@ -3747,4 +3747,8 @@ No match
     Ӆ\x0a
 No match
 
+/\C(\W?ſ)'?{{/utf
+    \\C(\\W?ſ)'?{{
+No match
+
 # End of testinput4