Re: [PATCH] hw/acpi/erst.c: Fix memset argument order

[Alexander Bulekov]

On 221023 1637, Christian A. Ehrhardt wrote:
> 
> Hi,
> 
> On Sat, Oct 22, 2022 at 01:37:27AM -0400, Alexander Bulekov wrote:
> > On 221021 1505, Alexander Bulekov wrote:
> > > On 221019 2115, Christian A. Ehrhardt wrote:
> > > > Fix memset argument order: The second argument is
> > > > the value, the length goes last.
> > > > 
> > > > Cc: Eric DeVolder <eric.devolder@oracle.com>
> > > > Cc: qemu-stable@nongnu.org
> > > > Fixes: f7e26ffa590 ("ACPI ERST: support for ACPI ERST feature")
> > > > Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
> > > > ---
> > > >  hw/acpi/erst.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/hw/acpi/erst.c b/hw/acpi/erst.c
> > > > index df856b2669..26391f93ca 100644
> > > > --- a/hw/acpi/erst.c
> > > > +++ b/hw/acpi/erst.c
> > > > @@ -716,7 +716,7 @@ static unsigned write_erst_record(ERSTDeviceState 
> > > > *s)
> > > >      if (nvram) {
> > > >          /* Write the record into the slot */
> > > >          memcpy(nvram, exchange, record_length);
> > > > -        memset(nvram + record_length, exchange_length - record_length, 
> > > > 0xFF);
> > > > +        memset(nvram + record_length, 0xFF, exchange_length - 
> > > > record_length);
> > > 
> > > Hi, 
> > > I'm running the fuzzer over this code. So far, it hasn't complained
> > > about this particular memset call, but it has crashed on the memcpy,
> > > directly preceding it. I think the record_length checks might be
> > > insufficient. I made an issue/reproducer:
> > > https://gitlab.com/qemu-project/qemu/-/issues/1268
> > > 
> > > In that particular case, record_length is ffffff00 and passes the
> > > checks. I'll keep an eye on the fuzzer to see if it will be able to
> > > crash the memset.
> > 
> > Here's a testcase for the memset issue:
> 
> Looks like this check in {read,write}_erst_record():
> |   if ((s->record_offset + record_length) > exchange_length) {
> |       return STATUS_FAILED;
> |   }
> 
> has an integer overrun and should be re-written as:
> |   if (record_length > exchange_length - s->record_offset) {
> |       return STATUS_FAILED;
> |   }
> 
>        regards    Christian

Hi Christian,
With this change applied (along with the memset fix), the fuzzer doesn't
find any crashes.
Thanks
-Alex