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[base] Avoid UB with memcpy

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`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
This commit is contained in:
Ben Wagner 2023-08-15 11:30:26 -04:00
parent a20de84e16
commit a9793feace
1 changed files with 6 additions and 2 deletions
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8
src/base/ftstream.c
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@ -141,7 +141,9 @@
if ( read_bytes > count )
read_bytes = count;
FT_MEM_COPY( buffer, stream->base + pos, read_bytes );
/* Allow "reading" zero bytes without UB even if buffer is NULL */
if ( count )
FT_MEM_COPY( buffer, stream->base + pos, read_bytes );
}
stream->pos = pos + read_bytes;
@ -178,7 +180,9 @@
if ( read_bytes > count )
read_bytes = count;
FT_MEM_COPY( buffer, stream->base + stream->pos, read_bytes );
/* Allow "reading" zero bytes without UB even if buffer is NULL */
if ( count )
FT_MEM_COPY( buffer, stream->base + stream->pos, read_bytes );
}
stream->pos += read_bytes;