Re: [Qemu-devel] [PATCH v2 4/5] qcow2: Check L1/L2/reftable entries for alignment

[Max Reitz <mreitz@redhat.com>]

On 08.09.2014 16:40, Benoît Canet wrote:
> The Friday 05 Sep 2014 à 16:07:18 (+0200), Max Reitz wrote :
>> Offsets taken from the L1, L2 and refcount tables are generally assumed
>> to be correctly aligned. However, this cannot be guaranteed if the image
>> has been written to by something different than qemu, thus check all
>> offsets taken from these tables for correct cluster alignment.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block/qcow2-cluster.c  | 43 ++++++++++++++++++++++++++++++++++++++++---
>>   block/qcow2-refcount.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
>>   2 files changed, 82 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
>> index 735f687..f7dd8c0 100644
>> --- a/block/qcow2-cluster.c
>> +++ b/block/qcow2-cluster.c
>> @@ -486,6 +486,13 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
>>           goto out;
>>       }
>>   
>> +    if (offset_into_cluster(s, l2_offset)) {
>> +        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
>> +                                " unaligned (L1 index: %#" PRIx64 ")",
>> +                                l2_offset, l1_index);
>> +        return -EIO;
> This function mix return ret and goto out and there is more of the second.
> Can we do ret = -EIO and goto out for consistency ?
> bs->drv == NULL after qcow2_signal_corruption so we are not afraid of out
> sides effects.

The "out" label here is for success; that's why I introduced the "fail" 
label in this series. I could make qcow2_cache_put() in the fail path 
optional and then use goto fail, though. But this would only increase 
the code size with no real benefit apparent to me (no code 
deduplication; and as far as I remember, we have many functions with 
fail labels which however use a plain "return" before cleaning up is 
needed).

(before this patch, there were two places using "goto out" in this 
function, both of which were "successes" (cluster found to be 
unallocated)); and two places using "return -errno", both of which were 
failures (the first one due to l2_load() failing and the second one due 
to a zero cluster found in a pre-v3 image))

Max

>> +    }
>> +
>>       /* load the l2 table in memory */
>>   
>>       ret = l2_load(bs, l2_offset, &l2_table);
>> @@ -508,8 +515,11 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
>>           break;
>>       case QCOW2_CLUSTER_ZERO:
>>           if (s->qcow_version < 3) {
>> -            qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
>> -            return -EIO;
>> +            qcow2_signal_corruption(bs, true, -1, -1, "Zero cluster entry found"
>> +                                    " in pre-v3 image (L2 offset: %#" PRIx64
>> +                                    ", L2 index: %#x)", l2_offset, l2_index);
>> +            ret = -EIO;
>> +            goto fail;
>>           }
>>           c = count_contiguous_clusters(nb_clusters, s->cluster_size,
>>                   &l2_table[l2_index], QCOW_OFLAG_ZERO);
>> @@ -525,6 +535,14 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
>>           c = count_contiguous_clusters(nb_clusters, s->cluster_size,
>>                   &l2_table[l2_index], QCOW_OFLAG_ZERO);
>>           *cluster_offset &= L2E_OFFSET_MASK;
>> +        if (offset_into_cluster(s, *cluster_offset)) {
>> +            qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset %#"
>> +                                    PRIx64 " unaligned (L2 offset: %#" PRIx64
>> +                                    ", L2 index: %#x)", *cluster_offset,
>> +                                    l2_offset, l2_index);
>> +            ret = -EIO;
>> +            goto fail;
>> +        }
>>           break;
>>       default:
>>           abort();
>> @@ -541,6 +559,10 @@ out:
>>       *num = nb_available - index_in_cluster;
>>   
>>       return ret;
>> +
>> +fail:
>> +    qcow2_cache_put(bs, s->l2_table_cache, (void **)&l2_table);
>> +    return ret;
>>   }
>>   
>>   /*
>> @@ -576,6 +598,12 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
>>   
>>       assert(l1_index < s->l1_size);
>>       l2_offset = s->l1_table[l1_index] & L1E_OFFSET_MASK;
>> +    if (offset_into_cluster(s, l2_offset)) {
>> +        qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#" PRIx64
>> +                                " unaligned (L1 index: %#" PRIx64 ")",
>> +                                l2_offset, l1_index);
>> +        return -EIO;
>> +    }
>>   
>>       /* seek the l2 table of the given l2 offset */
>>   
>> @@ -948,6 +976,15 @@ static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
>>           bool offset_matches =
>>               (cluster_offset & L2E_OFFSET_MASK) == *host_offset;
>>   
>> +        if (offset_into_cluster(s, cluster_offset & L2E_OFFSET_MASK)) {
>> +            qcow2_signal_corruption(bs, true, -1, -1, "Data cluster offset "
>> +                                    "%#llx unaligned (guest offset: %#" PRIx64
>> +                                    ")", cluster_offset & L2E_OFFSET_MASK,
>> +                                    guest_offset);
>> +            ret = -EIO;
>> +            goto out;
>> +        }
>> +
>>           if (*host_offset != 0 && !offset_matches) {
>>               *bytes = 0;
>>               ret = 0;
>> @@ -979,7 +1016,7 @@ out:
>>   
>>       /* Only return a host offset if we actually made progress. Otherwise we
>>        * would make requirements for handle_alloc() that it can't fulfill */
>> -    if (ret) {
>> +    if (ret > 0) {
>>           *host_offset = (cluster_offset & L2E_OFFSET_MASK)
>>                        + offset_into_cluster(s, guest_offset);
>>       }
>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
>> index b9d421e..2bcaaf9 100644
>> --- a/block/qcow2-refcount.c
>> +++ b/block/qcow2-refcount.c
>> @@ -108,6 +108,13 @@ static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
>>       if (!refcount_block_offset)
>>           return 0;
>>   
>> +    if (offset_into_cluster(s, refcount_block_offset)) {
>> +        qcow2_signal_corruption(bs, true, -1, -1, "Refblock offset %#" PRIx64
>> +                                " unaligned (reftable index: %#" PRIx64 ")",
>> +                                refcount_block_offset, refcount_table_index);
>> +        return -EIO;
>> +    }
>> +
>>       ret = qcow2_cache_get(bs, s->refcount_block_cache, refcount_block_offset,
>>           (void**) &refcount_block);
>>       if (ret < 0) {
>> @@ -181,6 +188,14 @@ static int alloc_refcount_block(BlockDriverState *bs,
>>   
>>           /* If it's already there, we're done */
>>           if (refcount_block_offset) {
>> +            if (offset_into_cluster(s, refcount_block_offset)) {
>> +                qcow2_signal_corruption(bs, true, -1, -1, "Refblock offset %#"
>> +                                        PRIx64 " unaligned (reftable index: "
>> +                                        "%#x)", refcount_block_offset,
>> +                                        refcount_table_index);
>> +                return -EIO;
>> +            }
>> +
>>                return load_refcount_block(bs, refcount_block_offset,
>>                    (void**) refcount_block);
>>           }
>> @@ -836,8 +851,14 @@ void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
>>       case QCOW2_CLUSTER_NORMAL:
>>       case QCOW2_CLUSTER_ZERO:
>>           if (l2_entry & L2E_OFFSET_MASK) {
>> -            qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
>> -                                nb_clusters << s->cluster_bits, type);
>> +            if (offset_into_cluster(s, l2_entry & L2E_OFFSET_MASK)) {
>> +                qcow2_signal_corruption(bs, false, -1, -1,
>> +                                        "Cannot free unaligned cluster %#llx",
>> +                                        l2_entry & L2E_OFFSET_MASK);
>> +            } else {
>> +                qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
>> +                                    nb_clusters << s->cluster_bits, type);
>> +            }
>>           }
>>           break;
>>       case QCOW2_CLUSTER_UNALLOCATED:
>> @@ -901,6 +922,14 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>>               old_l2_offset = l2_offset;
>>               l2_offset &= L1E_OFFSET_MASK;
>>   
>> +            if (offset_into_cluster(s, l2_offset)) {
>> +                qcow2_signal_corruption(bs, true, -1, -1, "L2 table offset %#"
>> +                                        PRIx64 " unaligned (L1 index: %#x)",
>> +                                        l2_offset, i);
>> +                ret = -EIO;
>> +                goto fail;
>> +            }
>> +
>>               ret = qcow2_cache_get(bs, s->l2_table_cache, l2_offset,
>>                   (void**) &l2_table);
>>               if (ret < 0) {
>> @@ -933,6 +962,17 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>>   
>>                       case QCOW2_CLUSTER_NORMAL:
>>                       case QCOW2_CLUSTER_ZERO:
>> +                        if (offset_into_cluster(s, offset & L2E_OFFSET_MASK)) {
>> +                            qcow2_signal_corruption(bs, true, -1, -1, "Data "
>> +                                                    "cluster offset %#llx "
>> +                                                    "unaligned (L2 offset: %#"
>> +                                                    PRIx64 ", L2 index: %#x)",
>> +                                                    offset & L2E_OFFSET_MASK,
>> +                                                    l2_offset, j);
>> +                            ret = -EIO;
>> +                            goto fail;
>> +                        }
>> +
>>                           cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits;
>>                           if (!cluster_index) {
>>                               /* unallocated */
>> -- 
>> 2.1.0
>>
>>