RE: [PATCH v4] qcow2-bitmap: Fix uint64_t left-shift overflow

[Tuguoyi]

On 01.11.2019 18:09, Vladimir Sementsov-Ogievskiy wrote:
> 01.11.2019 12:34, Tuguoyi wrote:
> > On 01.11.2019 17:25 Vladimir Sementsov-Ogievskiy wrote:
> >> 01.11.2019 10:37, Tuguoyi wrote:
> >>> There are two issues in In check_constraints_on_bitmap(),
> >>> 1) The sanity check on the granularity will cause uint64_t integer
> >>> left-shift overflow when cluster_size is 2M and the granularity is
> >>> BIGGER than 32K.
> >>> 2) The way to calculate image size that the maximum bitmap supported
> >>> can map to is a bit incorrect.
> >>> This patch fix it by add a helper function to calculate the number
> >>> of bytes needed by a normal bitmap in image and compare it to the
> >>> maximum bitmap bytes supported by qemu.
> >>>
> >>> Fixes: 5f72826e7fc62167cf3a
> >>> Signed-off-by: Guoyi Tu <address@hidden>
> >>
> >> You forget my
> >> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> >
> > Sorry for that, it's my first time to submit patch to qemu, and should I 
> > send
> another patch or not ?
> 
> Good start!
> 
> No, you shouldn't. Maintainer will take such marks (and may be other
> proposed improvements for commit message like this "Fixes: ", when applying,
> so no reason to resend.
> 
> Also, when sending a new version of patch, summarize what was changed
> since previous version (you may do it under "---" which follows commit
> message, or in cover letter if it's a patch set with several patches.

OK, I got it, thanks a lot. 

> >
> >> (I don't see changes except add "Fixes: " to commit msg and put
> >> get_bitmap_bytes_needed definition header into one line.)
> >
> > Yes, Only minor changes are made, including removing 'inline' keyword.
> >
> > Thanks for your patience in reviewing >
> >>> ---
> >>>    block/qcow2-bitmap.c | 14 +++++++++++---
> >>>    1 file changed, 11 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c index
> >>> 98294a7..ef9ef62 100644
> >>> --- a/block/qcow2-bitmap.c
> >>> +++ b/block/qcow2-bitmap.c
> >>> @@ -142,6 +142,13 @@ static int check_table_entry(uint64_t entry,
> >>> int
> >> cluster_size)
> >>>        return 0;
> >>>    }
> >>>
> >>> +static int64_t get_bitmap_bytes_needed(int64_t len, uint32_t
> >>> +granularity) {
> >>> +    int64_t num_bits = DIV_ROUND_UP(len, granularity);
> >>> +
> >>> +    return DIV_ROUND_UP(num_bits, 8); }
> >>> +
> >>>    static int check_constraints_on_bitmap(BlockDriverState *bs,
> >>>                                           const char *name,
> >>>                                           uint32_t granularity,
> @@
> >>> -150,6 +157,7 @@ static int
> >>> check_constraints_on_bitmap(BlockDriverState
> >> *bs,
> >>>        BDRVQcow2State *s = bs->opaque;
> >>>        int granularity_bits = ctz32(granularity);
> >>>        int64_t len = bdrv_getlength(bs);
> >>> +    int64_t bitmap_bytes;
> >>>
> >>>        assert(granularity > 0);
> >>>        assert((granularity & (granularity - 1)) == 0); @@ -171,9
> >>> +179,9 @@ static int check_constraints_on_bitmap(BlockDriverState *bs,
> >>>            return -EINVAL;
> >>>        }
> >>>
> >>> -    if ((len > (uint64_t)BME_MAX_PHYS_SIZE << granularity_bits) ||
> >>> -        (len > (uint64_t)BME_MAX_TABLE_SIZE * s->cluster_size <<
> >>> -               granularity_bits))
> >>> +    bitmap_bytes = get_bitmap_bytes_needed(len, granularity);
> >>> +    if ((bitmap_bytes > (uint64_t)BME_MAX_PHYS_SIZE) ||
> >>> +        (bitmap_bytes > (uint64_t)BME_MAX_TABLE_SIZE *
> >>> + s->cluster_size))
> >>>        {
> >>>            error_setg(errp, "Too much space will be occupied by the
> >> bitmap. "
> >>>                       "Use larger granularity");
> >>>
> >>
> >>
> >> --
> >> Best regards,
> >> Vladimir
> 
> 
> --
> Best regards,
> Vladimir