Fixed sre bug "[#581080] Provoking infinite scanner loops".

This bug happened because: 1) the scanner_search and scanner_match methods
were not checking the buffer limits before increasing the current pointer;
and 2) SRE_SEARCH was using "if (ptr == end)" as a loop break, instead of
"if (ptr >= end)".

* Modules/_sre.c
  (SRE_SEARCH): Check for "ptr >= end" to break loops, so that we don't
  hang forever if a pointer passing the buffer limit is used.
  (scanner_search,scanner_match): Don't increment the current pointer
  if we're going to pass the buffer limit.

* Misc/NEWS
  Mention the fix.

Misc/NEWS

@@ -359,6 +359,11 @@ Extension modules
   when running the expression r'(a)(b)?b' over 'ab', lastindex must be
   1, not 2.
 
+- Fixed bug #581080: sre scanner was not checking the buffer limit
+  before increasing the current pointer. This was creating an infinite
+  loop in the search function, once the pointer exceeded the buffer
+  limit.
+
 Library
 -------
 

Modules/_sre.c

@@ -1237,7 +1237,7 @@ SRE_SEARCH(SRE_STATE* state, SRE_CODE* pattern)
         for (;;) {
             while (ptr < end && (SRE_CODE) ptr[0] != chr)
                 ptr++;
-            if (ptr == end)
+            if (ptr >= end)
                 return 0;
             TRACE(("|%p|%p|SEARCH LITERAL\n", pattern, ptr));
             state->start = ptr;
@@ -1254,7 +1254,7 @@ SRE_SEARCH(SRE_STATE* state, SRE_CODE* pattern)
         for (;;) {
             while (ptr < end && !SRE_CHARSET(charset, ptr[0]))
                 ptr++;
-            if (ptr == end)
+            if (ptr >= end)
                 return 0;
             TRACE(("|%p|%p|SEARCH CHARSET\n", pattern, ptr));
             state->start = ptr;
@@ -2896,7 +2896,8 @@ scanner_match(ScannerObject* self, PyObject* args)
     match = pattern_new_match((PatternObject*) self->pattern,
                                state, status);
 
-    if (status == 0 || state->ptr == state->start)
+    if ((status == 0 || state->ptr == state->start) &&
+        state->ptr < state->end)
         state->start = (void*) ((char*) state->ptr + state->charsize);
     else
         state->start = state->ptr;
@@ -2927,7 +2928,8 @@ scanner_search(ScannerObject* self, PyObject* args)
     match = pattern_new_match((PatternObject*) self->pattern,
                                state, status);
 
-    if (status == 0 || state->ptr == state->start)
+    if ((status == 0 || state->ptr == state->start) &&
+        state->ptr < state->end)
         state->start = (void*) ((char*) state->ptr + state->charsize);
     else
         state->start = state->ptr;