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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Oct 24, 2022 at 09:20:40AM -0400, Alexander Bulekov wrote:
> 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

Thanks!
Christian, are you doing to be sending a combined patch for the whole
issue? If you do pls add Tested-by tags as appropriate. Thanks!

-- 
MST