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qcow2-cluster: Fix integer left shift error in qcow2_alloc_cluster_link_l2() 

When calculating the offset, the result of left shift operation will be promoted
to type int64 automatically because the left operand of + operator is uint64_t.
but the result after integer promotion may be produce an error value for us and
trigger the following asserting error.

For example, consider i=0x2000, cluster_bits=18, the result of left shift
operation will be 0x80000000. Cause argument i is of signed integer type,
the result is automatically promoted to 0xffffffff80000000 which is not
we expected

The way to trigger the assertion error:
  qemu-img create -f qcow2 -o preallocation=full,cluster_size=256k tmpdisk 10G

This patch fix it by casting @i to uint64_t before doing left shift operation

Signed-off-by: Guoyi Tu <tu.guoyi@h3c.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 81ba90fe0c014f269621c283269b42ad@h3c.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
master
Tuguoyi 2020-08-05 09:22:58 +00:00 committed by Peter Maydell
parent 616dab9afc
commit 348fcc4f7a
1 changed files with 1 additions and 1 deletions
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2
block/qcow2-cluster.c
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@ -980,7 +980,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
assert(l2_index + m->nb_clusters <= s->l2_slice_size);
for (i = 0; i < m->nb_clusters; i++) {
uint64_t offset = cluster_offset + (i << s->cluster_bits);
uint64_t offset = cluster_offset + ((uint64_t)i << s->cluster_bits);
/* if two concurrent writes happen to the same unallocated cluster
* each write allocates separate cluster and writes data concurrently.
* The first one to complete updates l2 table with pointer to its