On Sun, Jun 14, 2020 at 07:40:53PM +0200, Stefano Brivio wrote:
> Yury Norov reports that bitmap_cut() will not produce the right outcome
> if src and dst partially overlap, with src pointing at some location
> after dst, because the memmove() affects src before we store the bits
> that we need to keep, that is, the bits preceding the cut -- as long as
> we the beginning of the cut is not aligned to a long.
>
> Fix this by storing those bits before the memmove().
>
> Note that this is just a theoretical concern so far, as the only user
> of this function, pipapo_drop() from the nftables set back-end
> implemented in net/netfilter/nft_set_pipapo.c, always supplies entirely
> overlapping src and dst.
LGTM as long as test cases are passed,
Reviewed-by: Andy Shevchenko <andriy.shevche...@linux.intel.com>
> Reported-by: Yury Norov <yury.no...@gmail.com>
> Fixes: 2092767168f0 ("bitmap: Introduce bitmap_cut(): cut bits and shift
> remaining")
> Signed-off-by: Stefano Brivio <sbri...@redhat.com>
> ---
> v2: No changes
>
> lib/bitmap.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 89260aa342d6..c5712e8f4c38 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -211,13 +211,13 @@ void bitmap_cut(unsigned long *dst, const unsigned long
> *src,
> unsigned long keep = 0, carry;
> int i;
>
> - memmove(dst, src, len * sizeof(*dst));
> -
> if (first % BITS_PER_LONG) {
> keep = src[first / BITS_PER_LONG] &
> (~0UL >> (BITS_PER_LONG - first % BITS_PER_LONG));
> }
>
> + memmove(dst, src, len * sizeof(*dst));
> +
> while (cut--) {
> for (i = first / BITS_PER_LONG; i < len; i++) {
> if (i < len - 1)
> --
> 2.27.0
>
--
With Best Regards,
Andy Shevchenko
