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Add protection against out-of-bounds read in ttconv
This commit adds to counter to track how many tables are read from the table directory and stops the search for further tables early if the total number of tables has been reached.
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extern/ttconv/pprdrv_tt.cpp

Lines changed: 30 additions & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -757,33 +757,36 @@ void ttfont_sfnts(TTStreamWriter& stream, struct TTFONT *font)
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** Find the tables we want and store there vital
758758
** statistics in tables[].
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*/
760-
for (x=0; x < 9; x++ )
761-
{
762-
do
763-
{
764-
diff = strncmp( (char*)ptr, table_names[x], 4 );
765-
766-
if ( diff > 0 ) /* If we are past it. */
767-
{
768-
tables[x].length = 0;
769-
diff = 0;
770-
}
771-
else if ( diff < 0 ) /* If we haven't hit it yet. */
772-
{
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ptr += 16;
774-
}
775-
else if ( diff == 0 ) /* Here it is! */
776-
{
777-
tables[x].newoffset = nextoffset;
778-
tables[x].checksum = getULONG( ptr + 4 );
779-
tables[x].oldoffset = getULONG( ptr + 8 );
780-
tables[x].length = getULONG( ptr + 12 );
781-
nextoffset += ( ((tables[x].length + 3) / 4) * 4 );
782-
count++;
783-
ptr += 16;
784-
}
785-
}
786-
while (diff != 0);
760+
ULONG num_tables_read = 0; /* Number of tables read from the directory */
761+
for (x = 0; x < 9; x++) {
762+
do {
763+
if (num_tables_read < font->numTables) {
764+
/* There are still tables to read from ptr */
765+
diff = strncmp((char*)ptr, table_names[x], 4);
766+
767+
if (diff > 0) { /* If we are past it. */
768+
tables[x].length = 0;
769+
diff = 0;
770+
} else if (diff < 0) { /* If we haven't hit it yet. */
771+
ptr += 16;
772+
num_tables_read++;
773+
} else if (diff == 0) { /* Here it is! */
774+
tables[x].newoffset = nextoffset;
775+
tables[x].checksum = getULONG( ptr + 4 );
776+
tables[x].oldoffset = getULONG( ptr + 8 );
777+
tables[x].length = getULONG( ptr + 12 );
778+
nextoffset += ( ((tables[x].length + 3) / 4) * 4 );
779+
count++;
780+
ptr += 16;
781+
num_tables_read++;
782+
}
783+
} else {
784+
/* We've read the whole table directory already */
785+
/* Some tables couldn't be found */
786+
tables[x].length = 0;
787+
break; /* Proceed to next tables[x] */
788+
}
789+
} while (diff != 0);
787790

788791
} /* end of for loop which passes over the table directory */
789792

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