From 5959f829a93c18ccf15715768317b58f5d9bf2d4 Mon Sep 17 00:00:00 2001 From: Stefano Brivio Date: Tue, 11 Aug 2020 18:34:29 -0700 Subject: [PATCH] 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. Fixes: 2092767168f0 ("bitmap: Introduce bitmap_cut(): cut bits and shift remaining") Reported-by: Yury Norov Signed-off-by: Stefano Brivio Signed-off-by: Andrew Morton Reviewed-by: Andy Shevchenko Cc: Rasmus Villemoes Cc: Pablo Neira Ayuso Link: http://lkml.kernel.org/r/cover.1592155364.git.sbrivio@redhat.com Link: http://lkml.kernel.org/r/003e38d4428cd6091ef00b5b03354f1bd7d9091e.1592155364.git.sbrivio@redhat.com Signed-off-by: Linus Torvalds --- lib/bitmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/bitmap.c b/lib/bitmap.c index 0364452b1617..c13d859bc7ab 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -212,13 +212,13 @@ 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)