On Thu, Jun 22, 2023 at 12:28:28PM -0400, Mike Snitzer wrote:
> On Sat, Jun 03 2023 at 10:52P -0400,
> Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > Otherwise subsequent code will dereference a misaligned
> > `struct dm_target_spec *`, which is undefined behavior.
> >
> > Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> > drivers/md/dm-ioctl.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
> > index cc77cf3d410921432eb0c62cdede7d55b9aa674a..34fa74c6a70db8aa67aaba3f6a2fc4f38ef736bc 100644
> > --- a/drivers/md/dm-ioctl.c
> > +++ b/drivers/md/dm-ioctl.c
> > @@ -1394,6 +1394,13 @@ static inline fmode_t get_mode(struct dm_ioctl *param)
> > static int next_target(struct dm_target_spec *last, uint32_t next, void *end,
> > struct dm_target_spec **spec, char **target_params)
> > {
> > + static_assert(_Alignof(struct dm_target_spec) <= 8,
> > + "struct dm_target_spec has excessive alignment requirements");
>
> Really not sure what you mean by "has excessive alignment requirements"...
This patch checks that struct dm_target_spec is 8-byte aligned. That is
okay if its alignment is 8 or less, but not if is 16 or more, so I added
a static assert to check that struct dm_target_spec indeed requires at
most 8-byte alignment. That said, “excessive alignment requirements” is
(as shown by you having to ask this question) a bad error message.
Would “must not require more than 8-byte alignment” be better?
> > + if (next % 8) {
> > + DMERR("Next target spec (offset %u) is not 8-byte aligned", next);
> > + return -EINVAL;
> > + }
> > +
> > *spec = (struct dm_target_spec *) ((unsigned char *) last + next);
> > *target_params = (char *) (*spec + 1);
> >
>
> But this patch and patches 2 and 3 need more review. I'd like Mikulas to review.
>
> I did pick up patches 4-6 for the upcoming 6.5 merge window.
Thanks!
> Note, please prefix with "dm ioctl" instead of "device-mapper".
Good to know, thanks! I have several additional patches written that
require patch 4. Should I send patches 1 through 3 in the same series
as well?
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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