qcow2: Assert that L2 table offsets fit in the L1 table

L1 table entries have a field to store the offset of an L2 table.
The rest of the bits of the entry are currently reserved except from
bit 63, which stores the COPIED flag.

The offset is always taken from the entry using L1E_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 L1 table, it is
never used when we write to it. Due to the limits set elsewhere in the
code QEMU can never produce L2 table offsets that don't fit in that
field so any such offset when allocating an L2 table would indicate a
bug in QEMU.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 30eca26c476a45c59bcd15ad086e6acb21f1533e..179aa2c728f76c136c0f5c0cf4c704f464d27819 100644 (file)
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -285,6 +285,9 @@ static int l2_allocate(BlockDriverState *bs, int l1_index)
         goto fail;
     }
 
+    /* The offset must fit in the offset field of the L1 table entry */
+    assert((l2_offset & L1E_OFFSET_MASK) == l2_offset);
+
     /* If we're allocating the table at offset 0 then something is wrong */
     if (l2_offset == 0) {
         qcow2_signal_corruption(bs, true, -1, -1, "Preventing invalid "