From cdc674c7360b59486f5e5aaaa44f7395d2e15888 Mon Sep 17 00:00:00 2001 From: Alberto Garcia Date: Wed, 14 Nov 2018 16:58:57 +0200 Subject: [PATCH] qcow2: Assert that refcount block offsets fit in the refcount table Refcount table entries have a field to store the offset of the refcount block. The rest of the bits of the entry are currently reserved. The offset is always taken from the entry using REFT_OFFSET_MASK to ensure that we only use the bits that belong to that field. While that mask is used every time we read from the refcount table, it is never used when we write to it. Due to the other constraints of the qcow2 format QEMU can never produce refcount block offsets that don't fit in that field so any such offset when allocating a refcount block would indicate a bug in QEMU. Signed-off-by: Alberto Garcia Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- block/qcow2-refcount.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 1c63ac244a..6f13d470d3 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -368,6 +368,9 @@ static int alloc_refcount_block(BlockDriverState *bs, return new_block; } + /* The offset must fit in the offset field of the refcount table entry */ + assert((new_block & REFT_OFFSET_MASK) == new_block); + /* If we're allocating the block at offset 0 then something is wrong */ if (new_block == 0) { qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid "