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qcow2: Fix broken snapshot table entries

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The only case where we currently reject snapshot table entries is when
they have too much extra data.  Fix them with qemu-img check -r all by
counting it as a corruption, reducing their extra_data_size, and then
letting qcow2_check_fix_snapshot_table() do the rest.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20191011152814.14791-11-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2019-10-11 17:28:08 +02:00
parent fe446b5da2
commit f91f1f159b
1 changed files with 56 additions and 11 deletions
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67
block/qcow2-snapshot.c
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@ -44,7 +44,23 @@ void qcow2_free_snapshots(BlockDriverState *bs)
s->nb_snapshots = 0;
}
int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
/*
* If @repair is true, try to repair a broken snapshot table instead
* of just returning an error:
*
* - If there were snapshots with too much extra metadata, increment
* *extra_data_dropped for each.
* This requires the caller to eventually rewrite the whole snapshot
* table, which requires cluster allocation. Therefore, this should
* be done only after qcow2_check_refcounts() made sure the refcount
* structures are valid.
* (In the meantime, the image is still valid because
* qcow2_check_refcounts() does not do anything with snapshots'
* extra data.)
*/
static int qcow2_do_read_snapshots(BlockDriverState *bs, bool repair,
int *extra_data_dropped,
Error **errp)
{
BDRVQcow2State *s = bs->opaque;
QCowSnapshotHeader h;
@ -64,6 +80,8 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
s->snapshots = g_new0(QCowSnapshot, s->nb_snapshots);
for(i = 0; i < s->nb_snapshots; i++) {
bool truncate_unknown_extra_data = false;
/* Read statically sized part of the snapshot header */
offset = ROUND_UP(offset, 8);
ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
@ -86,10 +104,21 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
name_size = be16_to_cpu(h.name_size);
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;
if (!repair) {
ret = -EFBIG;
error_setg(errp, "Too much extra metadata in snapshot table "
"entry %i", i);
error_append_hint(errp, "You can force-remove this extra "
"metadata with qemu-img check -r all\n");
goto fail;
}
fprintf(stderr, "Discarding too much extra metadata in snapshot "
"table entry %i (%" PRIu32 " > %u)\n",
i, sn->extra_data_size, QCOW_MAX_SNAPSHOT_EXTRA_DATA);
(*extra_data_dropped)++;
truncate_unknown_extra_data = true;
}
/* Read known extra data */
@ -113,18 +142,26 @@ int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
}
if (sn->extra_data_size > sizeof(extra)) {
/* Store unknown extra data */
size_t unknown_extra_data_size =
sn->extra_data_size - sizeof(extra);
uint64_t extra_data_end;
size_t unknown_extra_data_size;
extra_data_end = offset + sn->extra_data_size - sizeof(extra);
if (truncate_unknown_extra_data) {
sn->extra_data_size = QCOW_MAX_SNAPSHOT_EXTRA_DATA;
}
/* Store unknown extra data */
unknown_extra_data_size = sn->extra_data_size - sizeof(extra);
sn->unknown_extra_data = g_malloc(unknown_extra_data_size);
ret = bdrv_pread(bs->file, offset, sn->unknown_extra_data,
unknown_extra_data_size);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to read snapshot table");
error_setg_errno(errp, -ret,
"Failed to read snapshot table");
goto fail;
}
offset += unknown_extra_data_size;
offset = extra_data_end;
}
/* Read snapshot ID */
@ -163,6 +200,11 @@ fail:
return ret;
}
int qcow2_read_snapshots(BlockDriverState *bs, Error **errp)
{
return qcow2_do_read_snapshots(bs, false, NULL, errp);
}
/* add at the end of the file a new list of snapshots */
int qcow2_write_snapshots(BlockDriverState *bs)
{
@ -328,6 +370,7 @@ int coroutine_fn qcow2_check_read_snapshot_table(BlockDriverState *bs,
{
BDRVQcow2State *s = bs->opaque;
Error *local_err = NULL;
int extra_data_dropped = 0;
int ret;
struct {
uint32_t nb_snapshots;
@ -363,7 +406,8 @@ int coroutine_fn qcow2_check_read_snapshot_table(BlockDriverState *bs,
}
qemu_co_mutex_unlock(&s->lock);
ret = qcow2_read_snapshots(bs, &local_err);
ret = qcow2_do_read_snapshots(bs, fix & BDRV_FIX_ERRORS,
&extra_data_dropped, &local_err);
qemu_co_mutex_lock(&s->lock);
if (ret < 0) {
result->check_errors++;
@ -376,6 +420,7 @@ int coroutine_fn qcow2_check_read_snapshot_table(BlockDriverState *bs,
return ret;
}
result->corruptions += extra_data_dropped;
return 0;
}