[Git][freetype/freetype][master] * src/base/ftsystem.c (ft_ansi_stream_io): Avoid undefined behaviour.

[Werner Lemberg (@wl)]

Werner Lemberg pushed to branch master at FreeType / FreeType

Commits:

• 3f2ac7d8
  by Tamir Duberstein at 2023-02-25T05:20:57+01:00

  * src/base/ftsystem.c (ft_ansi_stream_io): Avoid undefined behaviour.
  Also short-circuit on `offset` to avoid checking `count` a second time when
  `ft_ansi_stream_io` is used for reading.
  
  Per ISO/IEC 9899:
  
    If an argument to a function has an invalid value (such as a value outside
    the domain of the function, or a pointer outside the address space of the
    program, or a null pointer, or apointer to non-modifiable storage when the
    corresponding parameter is not const-qualified) or a type (after
    promotion) not expected by a function with variable number of arguments,
    the behavior is undefined.  If a function argument is described as being
    an array, the pointer actually passed to the function shall have a value
    such that all address computations and accesses to objects (that would be
    valid if the pointer did point to the first element of such an array) are
    in fact valid.
  
  Per IEEE Std 1003.1:
  
    size_t fread(void *restrict ptr, size_t size, size_t nitems,
                 FILE *restrict stream);
  
    The `fread` function shall read into the array pointed to by `ptr` up to
    `nitems` elements whose size is specified by `size` in bytes, from the
    stream pointed to by `stream`.
  
  Since the first argument to `fread` is described as being an array, its
  behavior is undefined when that argument is a null pointer.
  
  Per the documentation on `ft_ansi_stream_io`:
  
    If `count' is zero (this is, the function is used for seeking), a non-zero
    return value indicates an error.
  
  Thus the intent is clear, and the call to `fread` can be skipped, avoiding
  undefined behaviour.
  

1 changed file:

• src/base/ftsystem.c

Changes:

src/base/ftsystem.c

---

...	...	@@ -219,7 +219,7 @@
219	219	FT_FILE* file;
220	220
221	221
222		- if ( !count && offset > stream->size )
	222	+ if ( offset > stream->size && !count )
223	223	return 1;
224	224
225	225	file = STREAM_FILE( stream );
...	...	@@ -227,6 +227,11 @@
227	227	if ( stream->pos != offset )
228	228	ft_fseek( file, (long)offset, SEEK_SET );
229	229
	230	+ /* Avoid calling `fread` with `buffer=NULL` and `count=0`, */
	231	+ /* which is undefined behaviour. */
	232	+ if ( !count )
	233	+ return 0;
	234	+
230	235	return (unsigned long)ft_fread( buffer, 1, count, file );
231	236	}
232	237

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