Re: [PATCH] vfio: hisi_acc_vfio_pci: fix integer overflow check in hisi_acc_vf_resume_write()

[Dan Carpenter]

On Tue, Jul 05, 2022 at 03:06:49PM -0300, Jason Gunthorpe wrote:
> On Tue, Jul 05, 2022 at 12:05:28PM +0300, Dan Carpenter wrote:
> > The casting on this makes the integer overflow check slightly wrong.
> > "len" is an unsigned long. "*pos" and "requested_length" are signed
> > long longs.  Imagine "len" is ULONG_MAX and "*pos" is 2.
> > "ULONG_MAX + 2 = 1". 
> 
> I wonder if this can happen, len is a kernel controlled value bounded
> by a memory allocation..
> 

Oh.  Smatch uses a model which says that all read/writes come from
vfs_write().  The problem with tracking kernel read/writes is that
recursion is tricky.  So Smatch just deletes those from the DB.

> > Fixes: b0eed085903e ("hisi_acc_vfio_pci: Add support for VFIO live migration")
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> 
> This code was copy and pasted from drivers/vfio/pci/mlx5/main.c, so it
> should be fixed too

Sure.

I created a static checker warning for this type of thing but it didn't
catch the issue in drivers/vfio/pci/mlx5/main.c because Smatch says that
the bug is impossible.  Which is true.

Smatch doesn't really parse rw_verify_area() accurately.  I just hard
coded that function as accepting values 0-1000000000 for both *ppos and
count.

regards,
dan carpenter