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Re: [Qemu-devel] [PATCH v2 04/37] hw/usb-storage: Check whether BB is in


From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v2 04/37] hw/usb-storage: Check whether BB is inserted
Date: Wed, 4 Mar 2015 15:39:20 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 04.03.2015 um 15:24 hat Max Reitz geschrieben:
> On 2015-03-04 at 09:20, Kevin Wolf wrote:
> >Am 04.03.2015 um 15:07 hat Max Reitz geschrieben:
> >>On 2015-03-04 at 09:02, Kevin Wolf wrote:
> >>>Am 09.02.2015 um 18:11 hat Max Reitz geschrieben:
> >>>>Only call bdrv_key_required() on the BlockDriverState if the
> >>>>BlockBackend has an inserted medium.
> >>>>
> >>>>Signed-off-by: Max Reitz <address@hidden>
> >>>>Reviewed-by: Eric Blake <address@hidden>
> >>>>---
> >>>>  hw/usb/dev-storage.c | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>>diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
> >>>>index 4539733..3123baf 100644
> >>>>--- a/hw/usb/dev-storage.c
> >>>>+++ b/hw/usb/dev-storage.c
> >>>>@@ -638,7 +638,7 @@ static void usb_msd_realize_storage(USBDevice *dev, 
> >>>>Error **errp)
> >>>>      usb_msd_handle_reset(dev);
> >>>>      s->scsi_dev = scsi_dev;
> >>>>-    if (bdrv_key_required(blk_bs(blk))) {
> >>>>+    if (blk_is_inserted(blk) && bdrv_key_required(blk_bs(blk))) {
> >>>>          if (cur_mon) {
> >>>>              monitor_read_bdrv_key_start(cur_mon, blk_bs(blk),
> >>>>                                          usb_msd_password_cb, s);
> >>>Why would bdrv_key_required() ever return true when no medium is
> >>>inserted? Sounds like a bug to me, like not resetting state correctly on
> >>>bdrv_close() of an encrypted image.
> >>The point is that blk_bs(blk) might be NULL.
> >This is not what blk_is_inserted() is checking. It happens to protect
> >you against segfaults because it's robust against using NULL, but with
> >an existing BDS, checking whether there is a medium inserted (in the
> >physical device for passthrough drivers) doesn't make sense.
> 
> Not right now it's not. See patch 6.

Patch 6 looks unrelated, at least in v2. But if you're trying to say
that I looked at the wrong version, you're right: It doesn't protect you
against segfaults at this point yet (which is okay, because blk->bs
can't be NULL yet), it only performs the misguided inserted check.

Doesn't answer my initial question or make that check any better.

Kevin



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