From: Stefano Brivio <sbrivio@xxxxxxxxxx> Subject: lib/bitmap.c: fix bitmap_cut() for partial overlapping case Patch series "lib: Fix bitmap_cut() for overlaps, add test" This patch (of 2): 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. Link: http://lkml.kernel.org/r/cover.1592155364.git.sbrivio@xxxxxxxxxx Link: http://lkml.kernel.org/r/003e38d4428cd6091ef00b5b03354f1bd7d9091e.1592155364.git.sbrivio@xxxxxxxxxx Fixes: 2092767168f0 ("bitmap: Introduce bitmap_cut(): cut bits and shift remaining") Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx> Reported-by: Yury Norov <yury.norov@xxxxxxxxx> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/bitmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/lib/bitmap.c~bitmap-fix-bitmap_cut-for-partial-overlapping-case +++ a/lib/bitmap.c @@ -212,13 +212,13 @@ void bitmap_cut(unsigned long *dst, cons 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) _
