Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Fri, 27 Apr 2018 13:05:43 +0200 | Subject | Re: [PATCH v2 2/3] ACPI: ensure acpi_parse_entries_array() does not access non-existent table data |
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On Tue, Apr 24, 2018 at 9:35 PM, Al Stone <ahs3@redhat.com> wrote: > For ACPI tables that have subtables, acpi_parse_entries_array() gets used > to step through each of the subtables in memory. The primary loop for this > was checking that the beginning location of the subtable being examined > plus the length of struct acpi_subtable_header was not beyond the end of > the complete ACPI table; if it wasn't, the subtable could be examined, but > if it was the loop would terminate as it should. > > In the middle of this subtable loop, a callback is used to examine the > subtable in detail. > > Should the callback function try to examine elements of the subtable that > are located past the subtable header, and the ACPI table containing this > subtable has an incorrect length, it is possible to access either invalid > or protected memory and cause a fault. And, the length of struct > acpi_subtable_header will always be smaller than the length of the actual > subtable. > > To fix this, we make the main loop check that the beginning of the > subtable being examined plus the actual length of the subtable does > not go past the end of the enclosing ACPI table. While this cannot > protect us from malicious callback functions, it can prevent us from > failing because of some poorly constructed ACPI tables. > > Found by inspection. There is no functional change to existing code > that is known to work when calling acpi_parse_entries_array(). > > Signed-off-by: Al Stone <ahs3@redhat.com> > Cc: Rafael J. Wysocki <rjw@rjwysocki.net> > Cc: Len Brown <lenb@kernel.org> > --- > drivers/acpi/tables.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c > index 21535762b890..c7b028f231a6 100644 > --- a/drivers/acpi/tables.c > +++ b/drivers/acpi/tables.c > @@ -271,8 +271,7 @@ acpi_parse_entries_array(char *id, unsigned long table_size, > entry = (struct acpi_subtable_header *) > ((unsigned long)table_header + table_size); > > - while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) < > - table_end) { > + while (((unsigned long)entry + entry->length) <= table_end) {
The inner parens are not needed.
> if (max_entries && count >= max_entries) > break; > > --
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