[Git][freetype/freetype][master] [base] Avoid UB with memcpy

[Ben Wagner (@bungeman)]

Ben Wagner pushed to branch master at FreeType / FreeType

Commits:

• a9793fea
  by Ben Wagner at 2023-08-17T13:25:31-04:00

  [base] Avoid UB with memcpy
  
  `FT_NEW_ARRAY(p, 0)` sets `p` to `NULL`. `FT_Stream_ReadAt` with a
  memory based stream uses `FT_MEM_COPY` which is `memcpy` which specifies
  that it is undefined behavior for either the `src` or `dst` to be
  `NULL`. Instead of forcing all callers work around calling
  `FT_Stream_Read` when `buffer == NULL && count == 0` do the check in
  `FT_StreamRead`. This allows any call with `count == 0` to succesfully
  read zero bytes without UB.
  
  * src/base/ftstream.c (FT_Stream_ReadAt): skip `FT_MEM_COPY` when
  `count == 0`. (FT_Stream_TryRead): ditto
  
  Fixes: #1250
  

1 changed file:

• src/base/ftstream.c

Changes:

src/base/ftstream.c

---

...	...	@@ -141,7 +141,9 @@
141	141	if ( read_bytes > count )
142	142	read_bytes = count;
143	143
144		- FT_MEM_COPY( buffer, stream->base + pos, read_bytes );
	144	+ /* Allow "reading" zero bytes without UB even if buffer is NULL */
	145	+ if ( count )
	146	+ FT_MEM_COPY( buffer, stream->base + pos, read_bytes );
145	147	}
146	148
147	149	stream->pos = pos + read_bytes;
...	...	@@ -178,7 +180,9 @@
178	180	if ( read_bytes > count )
179	181	read_bytes = count;
180	182
181		- FT_MEM_COPY( buffer, stream->base + stream->pos, read_bytes );
	183	+ /* Allow "reading" zero bytes without UB even if buffer is NULL */
	184	+ if ( count )
	185	+ FT_MEM_COPY( buffer, stream->base + stream->pos, read_bytes );
182	186	}
183	187
184	188	stream->pos += read_bytes;

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