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qcow2: avoid misaligned 64bit bswap

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If we create a buffer directly on the stack by using 12 bytes, there's
no guarantee the 64bit value we want to swap will be aligned, which
could cause errors with undefined behavior.

Spotted with clang -fsanitize=undefined and observed in iotests 15, 26,
44, 115 and 121.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
John Snow 2015-11-02 18:32:06 -05:00 committed by Kevin Wolf
parent bcdce5a73c
commit 9533423063
1 changed files with 7 additions and 4 deletions
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11
block/qcow2-refcount.c
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@ -560,13 +560,16 @@ static int alloc_refcount_block(BlockDriverState *bs,
}
/* Hook up the new refcount table in the qcow2 header */
uint8_t data[12];
cpu_to_be64w((uint64_t*)data, table_offset);
cpu_to_be32w((uint32_t*)(data + 8), table_clusters);
struct QEMU_PACKED {
uint64_t d64;
uint32_t d32;
} data;
cpu_to_be64w(&data.d64, table_offset);
cpu_to_be32w(&data.d32, table_clusters);
BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_SWITCH_TABLE);
ret = bdrv_pwrite_sync(bs->file->bs,
offsetof(QCowHeader, refcount_table_offset),
data, sizeof(data));
&data, sizeof(data));
if (ret < 0) {
goto fail_table;
}