Re: [PATCH v2 03/15] NTB: Fix UB/bug in ntb_mw_get_align()

Jon Mason
2017-12-05T18:08:46Z

On Tue, Dec 5, 2017 at 12:56 PM, Serge Semin <fancer.lancer@gmail.com> wrote:
> On Tue, Dec 05, 2017 at 11:52:32AM -0500, Jon Mason <jdmason@kudzu.us> wrote:
>> On Sun, Dec 3, 2017 at 2:17 PM, Serge Semin <fancer.lancer@gmail.com> wrote:
>> > Simple (1 << pidx) operation causes undefined behaviour when
>> > pidx >= 32. It must be casted to u64 to match the actual return
>> > value of ntb_link_is_up() method, so to have all the possible
>> > peer indexes covered and to get rid of undefined behaviour.
>> > Additionally there are special macros in "linux/bitops.h" to perform
>> > the bit-set-shift operations, so it's recommended to have them used
>> > for proper bit setting.
>>
>> This looks good to me, but also seems like a bug fix. Please comment
>> on if this is not noticed.
>>
>
> The consequences of the bug isn't noticeable at the moment, but potentially
> it can be seen on the devices like Switchtec (when multi-portness is finally
> added). Anyway it's better to fix it now, than to wait for obvious bug.
> Additionally as I said the originator of the code should have used BIT_ULL
> instead of the pure bit shifting.

This is more of a question of whether it should go into -stable and be
outside this patch set. If this is impossible to ever hit, then
including it here instead of fast tracking it in -stable is fine.

Thanks,
Jon

>
> Thanks,
> -Sergey
>
>> Thanks,
>> Jon
>>
>> >
>> > Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
>> > Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
>> > ---
>> > include/linux/ntb.h | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/include/linux/ntb.h b/include/linux/ntb.h
>> > index c1646f2c6344..488e586fb76c 100644
>> > --- a/include/linux/ntb.h
>> > +++ b/include/linux/ntb.h
>> > @@ -764,7 +764,7 @@ static inline int ntb_mw_get_align(struct ntb_dev *ntb, int pidx, int widx,
>> > resource_size_t *size_align,
>> > resource_size_t *size_max)
>> > {
>> > - if (!(ntb_link_is_up(ntb, NULL, NULL) & (1 << pidx)))
>> > + if (!(ntb_link_is_up(ntb, NULL, NULL) & BIT_ULL(pidx)))
>> > return -ENOTCONN;
>> >
>> > return ntb->ops->mw_get_align(ntb, pidx, widx, addr_align, size_align,
>> > --
>> > 2.12.0
>> >