On Tue, Sep 24, 2024 at 10:44 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote:
>
> Hi Mikulas,
>
> On Tue, Sep 24, 2024 at 6:18 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> >
> > Maxim Suhanov reported that dm-verity doesn't crash if an I/O error
> > happens. In theory, this could be used to subvert security, because an
> > attacker can create sectors that return error with the Write Uncorrectable
> > command. Some programs may misbehave if they have to deal with EIO.
>
> I seem to recall that this was intentional. We used to restart/panic
> on I/O errors with FEC enabled, but the behavior was changed in commit
> 2c0468e054c0 ("dm verity: skip redundant verity_handle_err() on I/O
> errors"). Akilesh, do you remember what exactly was the issue here?
>
I looked at the history and the original intent and the idea stems
from this patch:
https://lore.kernel.org/dm-devel/b004e7c7-f795-77ed-19b9-983785780e92@xxxxxxxxx/T/#mec4df1ba3f3cb63846875fb2bfc1f8b3100f31f1
I think the EIO should be propagated back up the stack; I think this
will trigger panic
even for genuine I/O errors.
> > This commit fixes dm-verity, so that if "panic_on_corruption" or
> > "restart_on_corruption" was specified and an I/O error happens, the
> > machine will panic or restart.
> >
> > This commit also changes kernel_restart to emergency_restart -
> > kernel_restart calls reboot notifiers and these reboot notifiers may wait
> > for the bio that failed. emergency_restart doesn't call the notifiers.
> >
> > Reported-by: Maxim Suhanov <dfirblog@xxxxxxxxx>
> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> >
> > ---
> > drivers/md/dm-verity-target.c | 15 ++++++++++++++-
> > 1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/drivers/md/dm-verity-target.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/md/dm-verity-target.c 2024-09-23 17:48:08.000000000 +0200
> > +++ linux-2.6/drivers/md/dm-verity-target.c 2024-09-24 11:34:08.000000000 +0200
> > @@ -273,7 +273,7 @@ out:
> > return 0;
> >
> > if (v->mode == DM_VERITY_MODE_RESTART)
> > - kernel_restart("dm-verity device corrupted");
> > + emergency_restart();
>
> Can we still log the reason for the restart? I remember some folks
> used to rely on the "dm-verity device corrupted" message in the kernel
> log.
>
> Sami
