From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:39186) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gpbo7-0007nq-Rl for qemu-devel@nongnu.org; Fri, 01 Feb 2019 11:36:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gpbo5-00006p-O3 for qemu-devel@nongnu.org; Fri, 01 Feb 2019 11:36:47 -0500 From: Kevin Wolf Date: Fri, 1 Feb 2019 17:34:54 +0100 Message-Id: <20190201163518.31157-4-kwolf@redhat.com> In-Reply-To: <20190201163518.31157-1-kwolf@redhat.com> References: <20190201163518.31157-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Subject: [Qemu-devel] [PULL 03/27] qcow2: Assert that refcount block offsets fit in the refcount table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org From: Alberto Garcia Refcount table entries have a field to store the offset of the refcount block. The rest of the bits of the entry are currently reserved. The offset is always taken from the entry using REFT_OFFSET_MASK to ensure that we only use the bits that belong to that field. While that mask is used every time we read from the refcount table, it is never used when we write to it. Due to the other constraints of the qcow2 format QEMU can never produce refcount block offsets that don't fit in that field so any such offset when allocating a refcount block would indicate a bug in QEMU. Signed-off-by: Alberto Garcia Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block/qcow2-refcount.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 1c63ac244a..6f13d470d3 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -368,6 +368,9 @@ static int alloc_refcount_block(BlockDriverState *bs, return new_block; } =20 + /* The offset must fit in the offset field of the refcount table ent= ry */ + assert((new_block & REFT_OFFSET_MASK) =3D=3D new_block); + /* If we're allocating the block at offset 0 then something is wrong= */ if (new_block =3D=3D 0) { qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid " --=20 2.20.1