Commit bd41700773880ca049a331a9b8a079cf0b0311d4
2022-09-26T14:46:42
[sfnt] Add SVG document bounds checking. Add a check that the document content is actually contained within the `SVG ` table. Without this check a malformed font may claim arbitrary memory as its document content. * src/sfnt/ttsvg.c (tt_face_load_svg): Take `numEntries` into account when testing 'documentRecord' extents. (find_doc): Rename `stream` to `document_records` for clarity. (tt_face_load_svg_doc): Split `doc` from `doc_list` pointer for clarity. Test that the document content is contained within the table. Ensure minimum length of document before testing for gzip format. Reported as https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=51812
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diff --git a/src/sfnt/ttsvg.c b/src/sfnt/ttsvg.c
index 69277da..1c1df7b 100644
--- a/src/sfnt/ttsvg.c
+++ b/src/sfnt/ttsvg.c
@@ -114,7 +114,7 @@
FT_TRACE3(( "version: %d\n", svg->version ));
FT_TRACE3(( "number of entries: %d\n", svg->num_entries ));
- if ( offsetToSVGDocumentList +
+ if ( offsetToSVGDocumentList + 2U +
svg->num_entries * SVG_DOCUMENT_RECORD_SIZE > table_size )
goto InvalidTable;
@@ -196,7 +196,7 @@
static FT_Error
- find_doc( FT_Byte* stream,
+ find_doc( FT_Byte* document_records,
FT_UShort num_entries,
FT_UInt glyph_index,
FT_ULong *doc_offset,
@@ -225,8 +225,8 @@
return error;
}
- start_doc = extract_svg_doc( stream + start_index * 12 );
- end_doc = extract_svg_doc( stream + end_index * 12 );
+ start_doc = extract_svg_doc( document_records + start_index * 12 );
+ end_doc = extract_svg_doc( document_records + end_index * 12 );
if ( ( compare_svg_doc( start_doc, glyph_index ) == -1 ) ||
( compare_svg_doc( end_doc, glyph_index ) == 1 ) )
@@ -238,18 +238,18 @@
while ( start_index <= end_index )
{
i = ( start_index + end_index ) / 2;
- mid_doc = extract_svg_doc( stream + i * 12 );
+ mid_doc = extract_svg_doc( document_records + i * 12 );
comp_res = compare_svg_doc( mid_doc, glyph_index );
if ( comp_res == 1 )
{
start_index = i + 1;
- start_doc = extract_svg_doc( stream + start_index * 4 );
+ start_doc = extract_svg_doc( document_records + start_index * 4 );
}
else if ( comp_res == -1 )
{
end_index = i - 1;
- end_doc = extract_svg_doc( stream + end_index * 4 );
+ end_doc = extract_svg_doc( document_records + end_index * 4 );
}
else
{
@@ -283,38 +283,47 @@
tt_face_load_svg_doc( FT_GlyphSlot glyph,
FT_UInt glyph_index )
{
- FT_Byte* doc_list; /* pointer to the SVG doc list */
- FT_UShort num_entries; /* total number of entries in doc list */
- FT_ULong doc_offset;
- FT_ULong doc_length;
-
- FT_UShort start_glyph_id;
- FT_UShort end_glyph_id;
-
FT_Error error = FT_Err_Ok;
TT_Face face = (TT_Face)glyph->face;
FT_Memory memory = face->root.memory;
Svg* svg = (Svg*)face->svg;
+ FT_Byte* doc_list;
+ FT_ULong doc_limit;
+
+ FT_Byte* doc;
+ FT_ULong doc_offset;
+ FT_ULong doc_length;
+ FT_UShort doc_start_glyph_id;
+ FT_UShort doc_end_glyph_id;
+
FT_SVG_Document svg_document = (FT_SVG_Document)glyph->other;
FT_ASSERT( !( svg == NULL ) );
- doc_list = svg->svg_doc_list;
- num_entries = FT_NEXT_USHORT( doc_list );
+ doc_list = svg->svg_doc_list;
- error = find_doc( doc_list, num_entries, glyph_index,
- &doc_offset, &doc_length,
- &start_glyph_id, &end_glyph_id );
+ error = find_doc( doc_list + 2, svg->num_entries, glyph_index,
+ &doc_offset, &doc_length,
+ &doc_start_glyph_id, &doc_end_glyph_id );
if ( error != FT_Err_Ok )
goto Exit;
- doc_list = svg->svg_doc_list; /* reset, so we can use it again */
- doc_list = (FT_Byte*)( doc_list + doc_offset );
+ doc_limit = svg->table_size - ( doc_list - (FT_Byte*)svg->table );
+ if ( doc_offset > doc_limit ||
+ doc_length > doc_limit - doc_offset )
+ {
+ error = FT_THROW( Invalid_Table );
+ goto Exit;
+ }
+
+ doc = doc_list + doc_offset;
- if ( ( doc_list[0] == 0x1F ) && ( doc_list[1] == 0x8B )
- && ( doc_list[2] == 0x08 ) )
+ if ( doc_length > 6 &&
+ doc[0] == 0x1F &&
+ doc[1] == 0x8B &&
+ doc[2] == 0x08 )
{
#ifdef FT_CONFIG_OPTION_USE_ZLIB
@@ -331,10 +340,10 @@
* little-endian format.
*/
FT_TRACE4(( "SVG document is GZIP compressed\n" ));
- uncomp_size = (FT_ULong)doc_list[doc_length - 1] << 24 |
- (FT_ULong)doc_list[doc_length - 2] << 16 |
- (FT_ULong)doc_list[doc_length - 3] << 8 |
- (FT_ULong)doc_list[doc_length - 4];
+ uncomp_size = (FT_ULong)doc[doc_length - 1] << 24 |
+ (FT_ULong)doc[doc_length - 2] << 16 |
+ (FT_ULong)doc[doc_length - 3] << 8 |
+ (FT_ULong)doc[doc_length - 4];
if ( FT_QALLOC( uncomp_buffer, uncomp_size ) )
goto Exit;
@@ -342,7 +351,7 @@
error = FT_Gzip_Uncompress( memory,
uncomp_buffer,
&uncomp_size,
- doc_list,
+ doc,
doc_length );
if ( error )
{
@@ -353,7 +362,7 @@
glyph->internal->flags |= FT_GLYPH_OWN_GZIP_SVG;
- doc_list = uncomp_buffer;
+ doc = uncomp_buffer;
doc_length = uncomp_size;
#else /* !FT_CONFIG_OPTION_USE_ZLIB */
@@ -364,14 +373,14 @@
#endif /* !FT_CONFIG_OPTION_USE_ZLIB */
}
- svg_document->svg_document = doc_list;
+ svg_document->svg_document = doc;
svg_document->svg_document_length = doc_length;
svg_document->metrics = glyph->face->size->metrics;
svg_document->units_per_EM = glyph->face->units_per_EM;
- svg_document->start_glyph_id = start_glyph_id;
- svg_document->end_glyph_id = end_glyph_id;
+ svg_document->start_glyph_id = doc_start_glyph_id;
+ svg_document->end_glyph_id = doc_end_glyph_id;
svg_document->transform.xx = 0x10000;
svg_document->transform.xy = 0;
@@ -381,10 +390,10 @@
svg_document->delta.x = 0;
svg_document->delta.y = 0;
- FT_TRACE5(( "start_glyph_id: %d\n", start_glyph_id ));
- FT_TRACE5(( "end_glyph_id: %d\n", end_glyph_id ));
+ FT_TRACE5(( "start_glyph_id: %d\n", doc_start_glyph_id ));
+ FT_TRACE5(( "end_glyph_id: %d\n", doc_end_glyph_id ));
FT_TRACE5(( "svg_document:\n" ));
- FT_TRACE5(( " %.*s\n", (FT_UInt)doc_length, doc_list ));
+ FT_TRACE5(( " %.*s\n", (FT_UInt)doc_length, doc ));
glyph->other = svg_document;