[Git][freetype/freetype][master] [type1] Directly search for eexec in private dict

[Ben Wagner (@bungeman)]

Ben Wagner pushed to branch master at FreeType / FreeType

Commits:

• 90795210
  by Ben Wagner at 2022-06-16T14:51:57+00:00

  [type1] Directly search for eexec in private dict
  
  This code originally just searched for `eexec`. This was later modified
  to check that the `eexec` found is valid (not in a string or comment).
  This was done by searching for `eexec` as before and then, for each
  `eexec` found, searching from the beginning using the correct parsing to
  see if the `eexec` was still found. If the private dictionary is large
  and contains many copies of `eexec` which are not valid, the initial
  part of the private dictionary is scanned once for each, potentially
  leading to n^2 parsing time.
  
  Instead of finding an initial `eexec` and then re-parsing to discover if
  it is valid, drop the initial search for `eexec` and just parse to find
  a valid `eexec`. This is strictly faster since the validation must
  happen anyway and avoids restarting from the beginning each time an
  `eexec` is found in the data.
  
  * src/type1/t1parse.c (T1_Get_Private_Dict): avoid n^2 parsing
  
  Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1328883
  

1 changed file:

• src/type1/t1parse.c

Changes:

src/type1/t1parse.c

---

...	...	@@ -330,50 +330,25 @@
330	330	/* the private dict. Otherwise, simply overwrite into the base */
331	331	/* dictionary block in the heap. */
332	332
333		- /* first of all, look at the `eexec' keyword */
	333	+ /* First look for the `eexec' keyword. Ensure `eexec' is real -- */
	334	+ /* it could be in a comment or string (as e.g. in u003043t.gsf */
	335	+ /* from ghostscript). */
334	336	FT_Byte* cur = parser->base_dict;
335	337	FT_Byte* limit = cur + parser->base_len;
336	338	FT_Pointer pos_lf;
337	339	FT_Bool test_cr;
338	340
339	341
340		- Again:
341		- for (;;)
342		- {
343		- if ( cur[0] == 'e' &&
344		- cur + 9 < limit ) /* 9 = 5 letters for `eexec' + */
345		- /* whitespace + 4 chars */
346		- {
347		- if ( cur[1] == 'e' &&
348		- cur[2] == 'x' &&
349		- cur[3] == 'e' &&
350		- cur[4] == 'c' )
351		- break;
352		- }
353		- cur++;
354		- if ( cur >= limit )
355		- {
356		- FT_ERROR(( "T1_Get_Private_Dict:"
357		- " could not find `eexec' keyword\n" ));
358		- error = FT_THROW( Invalid_File_Format );
359		- goto Exit;
360		- }
361		- }
362		-
363		- /* check whether `eexec' was real -- it could be in a comment */
364		- /* or string (as e.g. in u003043t.gsf from ghostscript) */
365		-
366	342	parser->root.cursor = parser->base_dict;
367		- /* set limit to `eexec' + whitespace + 4 characters */
368		- parser->root.limit = cur + 10;
	343	+ parser->root.limit = parser->base_dict + parser->base_len;
369	344
370	345	cur = parser->root.cursor;
371	346	limit = parser->root.limit;
372	347
373	348	while ( cur < limit )
374	349	{
375		- if ( cur[0] == 'e' &&
376		- cur + 5 < limit )
	350	+ /* 9 = 5 letters for `eexec' + whitespace + 4 chars */
	351	+ if ( cur[0] == 'e' && cur + 9 < limit )
377	352	{
378	353	if ( cur[1] == 'e' &&
379	354	cur[2] == 'x' &&
...	...	@@ -389,21 +364,9 @@
389	364	cur = parser->root.cursor;
390	365	}
391	366
392		- /* we haven't found the correct `eexec'; go back and continue */
393		- /* searching */
394		-
395		- cur = limit;
396		- limit = parser->base_dict + parser->base_len;
397		-
398		- if ( cur >= limit )
399		- {
400		- FT_ERROR(( "T1_Get_Private_Dict:"
401		- " premature end in private dictionary\n" ));
402		- error = FT_THROW( Invalid_File_Format );
403		- goto Exit;
404		- }
405		-
406		- goto Again;
	367	+ FT_ERROR(( "T1_Get_Private_Dict: could not find `eexec' keyword\n" ));
	368	+ error = FT_THROW( Invalid_File_Format );
	369	+ goto Exit;
407	370
408	371	/* now determine where to write the _encrypted_ binary private */
409	372	/* dictionary. We overwrite the base dictionary for disk-based */

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