Re: [PATCH 2/4] ACPI: battery: Fix buffer overread if not NUL-terminated

[Armin Wolf]

Am 17.01.23 um 15:42 schrieb Rafael J. Wysocki:

> On Sat, Jan 14, 2023 at 9:51 AM Armin Wolf <W_Armin@xxxxxx> wrote:
> > If the buffer containing string data is not NUL-terminated
> > (which is perfectly legal according to the ACPI specification),
> > the acpi battery driver might not honor its length.
> Note that this is about extracting package entries of type ACPI_TYPE_BUFFER.
>
> And please spell ACPI in capitals.
>
> > Fix this by limiting the amount of data to be copied to
> > the buffer length while also using strscpy() to make sure
> > that the resulting string is always NUL-terminated.
> OK
>
> > Also use '\0' instead of a plain 0.
> Why?  It's a u8, not a char.
>
> > Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> > ---
> >   drivers/acpi/battery.c | 23 ++++++++++++++++-------
> >   1 file changed, 16 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> > index fb64bd217d82..9f6daa9f2010 100644
> > --- a/drivers/acpi/battery.c
> > +++ b/drivers/acpi/battery.c
> > @@ -438,15 +438,24 @@ static int extract_package(struct acpi_battery *battery,
> >                  if (offsets[i].mode) {
> >                          u8 *ptr = (u8 *)battery + offsets[i].offset;
> I would add
>
> u32 len = 32;
>
> > -                       if (element->type == ACPI_TYPE_STRING ||
> > -                           element->type == ACPI_TYPE_BUFFER)
> > +                       switch (element->type) {
> And here I would do
>
> case ACPI_TYPE_BUFFER:
>          if (len > element->buffer.length + 1)
>                  len = element->buffer.length + 1;
>
>          fallthrough;
> case ACPI_TYPE_STRING:
>          strscpy(ptr, element->buffer.pointer, len);
>          break;
> case ACPI_TYPE_INTEGER:
>
> and so on.

But wouldn't this cause the ACPI string object to be accessed the wrong way
(buffer.pointer instead of string.pointer)?

Armin Wolf

> > +                       case ACPI_TYPE_STRING:
> >                                  strscpy(ptr, element->string.pointer, 32);
> > -                       else if (element->type == ACPI_TYPE_INTEGER) {
> > -                               strncpy(ptr, (u8 *)&element->integer.value,
> > -                                       sizeof(u64));
> > +
> > +                               break;
> > +                       case ACPI_TYPE_BUFFER:
> > +                               strscpy(ptr, element->buffer.pointer,
> > +                                       min_t(u32, element->buffer.length + 1, 32));
> > +
> > +                               break;
> > +                       case ACPI_TYPE_INTEGER:
> > +                               strncpy(ptr, (u8 *)&element->integer.value, sizeof(u64));
> >                                  ptr[sizeof(u64)] = 0;
> > -                       } else
> > -                               *ptr = 0; /* don't have value */
> > +
> > +                               break;
> > +                       default:
> > +                               *ptr = '\0'; /* don't have value */
> > +                       }
> >                  } else {
> >                          int *x = (int *)((u8 *)battery + offsets[i].offset);
> >                          *x = (element->type == ACPI_TYPE_INTEGER) ?
> > --