Re: [PATCH v2 01/17] block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes

[Eric Blake]

On 4/29/20 12:05 AM, Vladimir Sementsov-Ogievskiy wrote:
> 29.04.2020 1:09, Eric Blake wrote:
> > On 4/27/20 3:23 AM, Vladimir Sementsov-Ogievskiy wrote:
> > > The function is called from 64bit io handlers, and bytes is just passed
> > > to throttle_account() which is 64bit too (unsigned though). So, let's
> > > convert intermediate argument to 64bit too.
> >
> > My audit for this patch:
> >
> > Caller has 32-bit, this patch now causes widening which is safe:
> > block/block-backend.c: blk_do_preadv() passes 'unsigned int'
> > block/block-backend.c: blk_do_pwritev_part() passes 'unsigned int'
> > block/throttle.c: throttle_co_pwrite_zeroes() passes 'int'
> > block/throttle.c: throttle_co_pdiscard() passes 'int'
> >
> > Caller has 64-bit, this patch fixes potential bug where pre-patch 
> > could narrow, except it's easy enough to trace that callers are still 
> > capped at 2G actions:
> > block/throttle.c: throttle_co_preadv() passes 'uint64_t'
> > block/throttle.c: throttle_co_pwritev() passes 'uint64_t'
> >
> > Implementation in question: block/throttle-groups.c 
> > throttle_group_co_io_limits_intercept() takes 'unsigned int bytes' and 
> > uses it:
> > argument to util/throttle.c throttle_account(uint64_t)
> >
> > All safe: it patches a latent bug, and does not introduce any 64-bit 
> > gotchas once throttle_co_p{read,write}v are relaxed, and assuming 
> > throttle_account() is not buggy.
>
> Should I add this all to commit message?

It never hurts to provide such rationale ;)

> > > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > > ---
> > >   include/block/throttle-groups.h | 2 +-
> > >   block/throttle-groups.c         | 2 +-
> > >   2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > Reviewed-by: Eric Blake <address@hidden>
>
> Thanks for careful review!

--
Eric Blake, Principal Software Engineer
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