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Tue, 20 Aug 2019 11:43:15 +0000 (UTC) To: Eric Blake , qemu-block@nongnu.org References: <20190819185602.4267-1-mreitz@redhat.com> <20190819185602.4267-5-mreitz@redhat.com> <85d04ded-0bf6-ab67-7af9-cc97f30ad366@redhat.com> From: Max Reitz Openpgp: preference=signencrypt 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: <9f41a69e-317e-b14b-30e9-59dadadb3c45@redhat.com> Date: Tue, 20 Aug 2019 13:43:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <85d04ded-0bf6-ab67-7af9-cc97f30ad366@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="aS42y3eB6W9xjs1HgXKAIRNF7INJxlQSE" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 20 Aug 2019 11:43:16 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 04/16] qcow2: Keep unknown extra snapshot data 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: Kevin Wolf , qemu-devel@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) --aS42y3eB6W9xjs1HgXKAIRNF7INJxlQSE Content-Type: multipart/mixed; boundary="8MLLZuDV6Wcm8FNSTEyAg6vbB17h7sWHy"; protected-headers="v1" From: Max Reitz To: Eric Blake , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Kevin Wolf Message-ID: <9f41a69e-317e-b14b-30e9-59dadadb3c45@redhat.com> Subject: Re: [PATCH v2 04/16] qcow2: Keep unknown extra snapshot data References: <20190819185602.4267-1-mreitz@redhat.com> <20190819185602.4267-5-mreitz@redhat.com> <85d04ded-0bf6-ab67-7af9-cc97f30ad366@redhat.com> In-Reply-To: <85d04ded-0bf6-ab67-7af9-cc97f30ad366@redhat.com> --8MLLZuDV6Wcm8FNSTEyAg6vbB17h7sWHy Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 19.08.19 21:34, Eric Blake wrote: > On 8/19/19 1:55 PM, Max Reitz wrote: >> The qcow2 specification says to ignore unknown extra data fields in >> snapshot table entries. Currently, we discard it whenever we update t= he >> image, which is a bit different from "ignore". >> >> This patch makes the qcow2 driver keep all unknown extra data fields >> when updating an image's snapshot table. >> >=20 >> @@ -80,31 +80,53 @@ int qcow2_read_snapshots(BlockDriverState *bs, Err= or **errp) >> sn->date_sec =3D be32_to_cpu(h.date_sec); >> sn->date_nsec =3D be32_to_cpu(h.date_nsec); >> sn->vm_clock_nsec =3D be64_to_cpu(h.vm_clock_nsec); >> - extra_data_size =3D be32_to_cpu(h.extra_data_size); >> + sn->extra_data_size =3D be32_to_cpu(h.extra_data_size); >> =20 >> id_str_size =3D be16_to_cpu(h.id_str_size); >> name_size =3D be16_to_cpu(h.name_size); >> =20 >> - /* Read extra data */ >> + if (sn->extra_data_size > QCOW_MAX_SNAPSHOT_EXTRA_DATA) { >> + ret =3D -EFBIG; >> + error_setg(errp, "Too much extra metadata in snapshot tab= le " >> + "entry %i", i); >> + goto fail; >=20 > We fail if extra_data_size is > 1024... >=20 >=20 >> + if (sn->extra_data_size > sizeof(extra)) { >> + /* Store unknown extra data */ >> + size_t unknown_extra_data_size =3D >> + sn->extra_data_size - sizeof(extra); >> + >=20 > But read at most 1008 bytes into sn->unknown_extra_data. >=20 >> @@ -234,6 +257,22 @@ static int qcow2_write_snapshots(BlockDriverState= *bs) >> } >> offset +=3D sizeof(extra); >> =20 >> + if (sn->extra_data_size > sizeof(extra)) { >> + size_t unknown_extra_data_size =3D >> + sn->extra_data_size - sizeof(extra); >> + >> + /* qcow2_read_snapshots() ensures no unbounded allocation= */ >> + assert(unknown_extra_data_size <=3D BDRV_REQUEST_MAX_BYTE= S); >=20 > So this assertion is quite loose in what it permits; tighter would be >=20 > assert(unknown_extra_data_size <=3D QCOW_MAX_SNAPSHOT_EXTRA_DATA - > sizeof(extra)) As I said in the last version, I have this assertion here just because of the following bdrv_pwrite(); so all we need to assert is that it fits BDRV_REQUEST_MAX_BYTES (which it clearly does, as you say). Max --8MLLZuDV6Wcm8FNSTEyAg6vbB17h7sWHy-- --aS42y3eB6W9xjs1HgXKAIRNF7INJxlQSE Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl1b3NIACgkQ9AfbAGHV z0AclQf9GWUusiyxUta87jpQGsqFXEJX0YlxyxlvWrzREtWf70mn8T6MvKzlz2aH mzq1LVToahYYORJlf7chwRX0aeo+OFINFqPVf7ecrFjXylQHqIT+JpIpb+xwTkn7 WAKIQ8omiJzaVP1SMrrQJJFOKCZ8kz56tXbt1twI0ZWxtQqZzLal3ajycWFyctSx DbfKpL1FQe2Wr6g/avdI+LeGOds//I61h9yJ5S5uVV/RTaN9ufs2RVDhzR0ifg6q 8E1mEsTpnia4Gs5Mme069d4u/wlWcVkF95P26S2FfkW1wwatIRNLvxiTD0PGCvAq /c+jMCGmrCTEWntr47N7ZCDED+l1pA== =Y9Tg -----END PGP SIGNATURE----- --aS42y3eB6W9xjs1HgXKAIRNF7INJxlQSE--