From 95334230637cef9fbd199bb79a56271ec73d4732 Mon Sep 17 00:00:00 2001 From: John Snow Date: Mon, 2 Nov 2015 18:32:06 -0500 Subject: qcow2: avoid misaligned 64bit bswap 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 Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block/qcow2-refcount.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) (limited to 'block/qcow2-refcount.c') diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 4b81c8db61..6e0e5bd9ae 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -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; } -- cgit v1.2.3