linux-kernel - [PATCH v3 12/14] lib/mpi: mpi_read_raw_from

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1458649047-1661-1-git-send-email-nicstange@gmail.com>
Date:	Tue, 22 Mar 2016 13:17:27 +0100
From:	Nicolai Stange <nicstange@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>
Cc:	Tadeusz Struk <tadeusz.struk@...el.com>,
	Michal Marek <mmarek@...e.com>,
	Andrzej Zaborowski <andrew.zaborowski@...el.com>,
	Stephan Mueller <smueller@...onox.de>,
	Arnd Bergmann <arnd@...db.de>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, Nicolai Stange <nicstange@...il.com>
Subject: [PATCH v3 12/14] lib/mpi: mpi_read_raw_from_sgl(): fix nbits calculation

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 <nicstange@...il.com>
---
 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 27703aa..24a0155 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);
-- 
2.7.4