From: Nicolai Stange Subject: [PATCH RESEND v2 12/14] lib/mpi: mpi_read_raw_from_sgl(): fix nbits calculation Date: Mon, 21 Mar 2016 14:26:13 +0100 Message-ID: <1458566775-5239-13-git-send-email-nicstange@gmail.com> References: <1458566775-5239-1-git-send-email-nicstange@gmail.com> Cc: Tadeusz Struk , Michal Marek , Andrzej Zaborowski , Stephan Mueller , Arnd Bergmann , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, Nicolai Stange To: Herbert Xu , "David S. Miller" Return-path: Received: from mail-wm0-f66.google.com ([74.125.82.66]:33572 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755997AbcCUN0w (ORCPT ); Mon, 21 Mar 2016 09:26:52 -0400 In-Reply-To: <1458566775-5239-1-git-send-email-nicstange@gmail.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: The number of bits, nbits, is calculated in mpi_read_raw_from_sgl() as follows: nbits = nbytes * 8; Afterwards, the number of leading zero bits of the first byte get subtracted: nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)); However, count_leading_zeros() takes an unsigned long and thus, the u8 gets promoted to an unsigned long. Thus, the above doesn't subtract the number of leading zeros in the most significant nonzero input byte from nbits, but the number of leading zeros of the most significant nonzero input byte promoted to unsigned long, i.e. BITS_PER_LONG - 8 too many. Fix this by subtracting count_leading_zeros(...) - (BITS_PER_LONG - 8) from nbits only. Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") Signed-off-by: Nicolai Stange --- lib/mpi/mpicoder.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c index 4cf8516..5d02efe 100644 --- a/lib/mpi/mpicoder.c +++ b/lib/mpi/mpicoder.c @@ -460,7 +460,8 @@ MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes) } if (nbytes > 0) - nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)); + nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)) - + (BITS_PER_LONG - 8); nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB); val = mpi_alloc(nlimbs); -- 2.7.3