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Re: [Qemu-devel] [PATCH v2 04/16] qcow2: Keep unknown extra snapshot dat
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v2 04/16] qcow2: Keep unknown extra snapshot data |
Date: |
Mon, 19 Aug 2019 14:34:54 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 |
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 the
> 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.
>
> @@ -80,31 +80,53 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error
> **errp)
> sn->date_sec = be32_to_cpu(h.date_sec);
> sn->date_nsec = be32_to_cpu(h.date_nsec);
> sn->vm_clock_nsec = be64_to_cpu(h.vm_clock_nsec);
> - extra_data_size = be32_to_cpu(h.extra_data_size);
> + sn->extra_data_size = be32_to_cpu(h.extra_data_size);
>
> id_str_size = be16_to_cpu(h.id_str_size);
> name_size = be16_to_cpu(h.name_size);
>
> - /* Read extra data */
> + if (sn->extra_data_size > QCOW_MAX_SNAPSHOT_EXTRA_DATA) {
> + ret = -EFBIG;
> + error_setg(errp, "Too much extra metadata in snapshot table "
> + "entry %i", i);
> + goto fail;
We fail if extra_data_size is > 1024...
> + if (sn->extra_data_size > sizeof(extra)) {
> + /* Store unknown extra data */
> + size_t unknown_extra_data_size =
> + sn->extra_data_size - sizeof(extra);
> +
But read at most 1008 bytes into sn->unknown_extra_data.
> @@ -234,6 +257,22 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
> }
> offset += sizeof(extra);
>
> + if (sn->extra_data_size > sizeof(extra)) {
> + size_t unknown_extra_data_size =
> + sn->extra_data_size - sizeof(extra);
> +
> + /* qcow2_read_snapshots() ensures no unbounded allocation */
> + assert(unknown_extra_data_size <= BDRV_REQUEST_MAX_BYTES);
So this assertion is quite loose in what it permits; tighter would be
assert(unknown_extra_data_size <= QCOW_MAX_SNAPSHOT_EXTRA_DATA -
sizeof(extra))
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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- [Qemu-devel] [PATCH v2 00/16] qcow2: Let check -r all repair some snapshot bits, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 01/16] include: Move endof() up from hw/virtio/virtio.h, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 02/16] qcow2: Use endof(), Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 03/16] qcow2: Add Error ** to qcow2_read_snapshots(), Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 04/16] qcow2: Keep unknown extra snapshot data, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 05/16] qcow2: Make qcow2_write_snapshots() public, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 06/16] qcow2: Put qcow2_upgrade() into its own function, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 07/16] qcow2: Write v3-compliant snapshot list on upgrade, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 08/16] qcow2: Separate qcow2_check_read_snapshot_table(), Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 09/16] qcow2: Add qcow2_check_fix_snapshot_table(), Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 11/16] qcow2: Keep track of the snapshot table length, Max Reitz, 2019/08/19
- [Qemu-devel] [PATCH v2 10/16] qcow2: Fix broken snapshot table entries, Max Reitz, 2019/08/19