On Tue, May 1, 2018 at 2:39 AM, Al Stone <ahs3@xxxxxxxxxx> 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@xxxxxxxxxx> > Cc: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> > Cc: Len Brown <lenb@xxxxxxxxxx> > --- > 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 4a3410aa6540..82c3e2c52dd9 100644 > --- a/drivers/acpi/tables.c > +++ b/drivers/acpi/tables.c > @@ -274,8 +274,7 @@ 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) { > if (max_entries && count >= max_entries) > break; > > -- This breaks the CPU enumeration on my Dell XPS13 9360 (possibly among other things), so I'm dropping it. I can send you acpidump output from that machine if need be. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html