Re: [XEN PATCH] libxl: Check return value of libxl__xs_directory in name2bdf

["G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>]

On Mon, Jul 11, 2022 at 7:03 PM Juergen Gross <jgross@xxxxxxxx> wrote:
>
> On 11.07.22 12:38, Anthony PERARD wrote:
> > libxl__xs_directory() can potentially return NULL without setting `n`.
> > As `n` isn't initialised, we need to check libxl__xs_directory()
> > return value before checking `n`. Otherwise, `n` might be non-zero
> > with `bdfs` NULL which would lead to a segv.
> >
> > Reported-by: "G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>
> > Fixes: 57bff091f4 ("libxl: add 'name' field to 'libxl_device_pci' in the 
> > IDL...")
> > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>
> Reviewed-by: Juergen Gross <jgross@xxxxxxxx>

Hi Anthony,

I can confirm that the change fixed the segment fault issue I observed
on 4.16.1 release.

However, the behavior is still not entirely clean after the fix. But
that's probably a separate issue.
I have two devices assigned to pckback through kernel command-line.
When I attempted to use pci-assignable-remove on the SSD that caused
me a lot of trouble, it fails on the first attempt but works fine
later...
root@gaia:~# xl pci-assignable-list
0000:00:17.0
0000:05:00.0
root@gaia:~# xl pci-assignable-remove 05:00.0
libxl: error: libxl_pci.c:906:libxl__device_pci_assignable_remove:
failed to de-quarantine 0000:05:00.0
root@gaia:~# xl pci-assignable-list
0000:00:17.0
0000:05:00.0
root@gaia:~# xl pci-assignable-add 05:00.0
libxl: warning: libxl_pci.c:802:libxl__device_pci_assignable_add:
0000:05:00.0 already assigned to pciback
root@gaia:~# xl pci-assignable-list
0000:00:17.0
0000:05:00.0
root@gaia:~# xl pci-assignable-remove 05:00.0
root@gaia:~# xl pci-assignable-list
0000:00:17.0
root@gaia:~# xl pci-assignable-add 05:00.0
libxl: warning: libxl_pci.c:822:libxl__device_pci_assignable_add:
0000:05:00.0 not bound to a driver, will not be rebound.
root@gaia:~# xl pci-assignable-list
0000:00:17.0
0000:05:00.0

I'm no longer in a debug environment, so cannot collect more debug
info right now.

Thanks,
G.R.