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Thu, 6 Feb 2020 17:36:44 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C978460F89; Thu, 6 Feb 2020 17:36:37 +0000 (UTC) Subject: Re: [PATCH] block: fix crash on zero-length unaligned write and read To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20200206164245.17781-1-vsementsov@virtuozzo.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Thu, 6 Feb 2020 18:36:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200206164245.17781-1-vsementsov@virtuozzo.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="in9zyM9S9k2s2A5mbfhXP1U6L6kbdJRuE" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, fam@euphon.net, qemu-devel@nongnu.org, stefanha@redhat.com, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --in9zyM9S9k2s2A5mbfhXP1U6L6kbdJRuE Content-Type: multipart/mixed; boundary="rBBcLTF1LKioX95McHy3E6Mgm6X49IAd8" --rBBcLTF1LKioX95McHy3E6Mgm6X49IAd8 Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 06.02.20 17:42, Vladimir Sementsov-Ogievskiy wrote: > Commit 7a3f542fbd "block/io: refactor padding" occasionally dropped > aligning for zero-length request: bdrv_init_padding() blindly return > false if bytes =3D=3D 0, like there is nothing to align. >=20 > This leads the following command to crash: >=20 > ./qemu-io --image-opts -c 'write 1 0' \ > driver=3Dblkdebug,align=3D512,image.driver=3Dnull-co,image.size=3D512 >=20 >>> qemu-io: block/io.c:1955: bdrv_aligned_pwritev: Assertion > `(offset & (align - 1)) =3D=3D 0' failed. >>> Aborted (core dumped) >=20 > Prior to 7a3f542fbd we does aligning of such zero requests. Instead of > recovering this behavior let's just do nothing on such requests as it > is useless. >=20 > Note that driver may have special meaning of zero-length reqeusts, like > qcow2_co_pwritev_compressed_part, so we can't skip any zero-length > operation. But for unaligned ones, we can't pass it to driver anyway. >=20 > This commit also fixes crash in iotest 80 running with -nocache: >=20 > ./check -nocache -qcow2 80 >=20 > which crashes on same assertion due to trying to read empty extra data > in qcow2_do_read_snapshots(). >=20 > Cc: qemu-stable@nongnu.org # v4.2 > Fixes: 7a3f542fbd > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > block/io.c | 28 +++++++++++++++++++++++++++- > 1 file changed, 27 insertions(+), 1 deletion(-) Zero-length reads would still trigger CORs when padded. But there is no reason to assume or rely on this, so: Reviewed-by: Max Reitz (block/io.c is Stefan=92s department. :-)) Max --rBBcLTF1LKioX95McHy3E6Mgm6X49IAd8-- --in9zyM9S9k2s2A5mbfhXP1U6L6kbdJRuE Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl48TqQACgkQ9AfbAGHV z0BO2wgAt2th9y1PawpD8fmlq4NlvJcaE2A7SC2X7F7hSLAJPYiXLlsnPym4c/nt haKEnLCqNXHlNpVhEYbS463L69XoJ1p8NPTuqHvUu9qqkk/i+sTVrwfprWtjMnbC bMUmCPO/ctb0xVRnWyKjiLAawXtvM67LtWqaCpvwK/CH9Ust9OoyGE1BCs8PHc9l He2uYuvuKHdUHl5MsqCPnHGeDMxa9uWwMMqBrAncRsc3OsHufz1Kv1NIdzC9zWVy k28FWAvKvYh+DtwI9eYo5i0aI5ISzX+ATJ8LJEwUBnPgYb92o6VHuIo2T5+OY/9k Q2eZtVkB4ePCXQf9BvsZKesgrXz+vw== =FkAa -----END PGP SIGNATURE----- --in9zyM9S9k2s2A5mbfhXP1U6L6kbdJRuE--