Re: [Qemu-devel] [PATCH v4 0/3] block: Fix unaligned bdrv_aio_write_zeroes

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/04/2015 15:18, Fam Zheng wrote:
> An unaligned zero write causes NULL deferencing in bdrv_co_do_pwritev. That
> path is reachable from bdrv_co_write_zeroes and bdrv_aio_write_zeroes.
> 
> You can easily trigger through the former with qemu-io, as the test case added
> by 61815d6e0aa. For bdrv_aio_write_zeroes, in common cases there's always a
> format driver (which uses 512 alignment), so it would be much rarer to have
> unaligned requests (only concerning top level here, when the request goes down
> to bs->file, where for example the alignment is 4k, it would then be calling
> bdrv_co_write_zeroes because it's in a coroutine).
> 
> fc3959e4669a1c fixed bdrv_co_write_zeroes but not bdrv_aio_write_zeroes.  The
> lattern is the actually used one by device model. Revert the previous fix, do
> it in bdrv_co_do_pwritev, to cover both paths.
> 
> v4: "if (!qiov)" -> "if (!qiov && bytes >= align)". (Paolo)
> 
> v3: Fix the case where the unaligned request is contained within the first
>     block. (Paolo)
>     Also update iotests 033 to cover the code path with qemu-io.
> 
> v2: Split to three aligned pwritev.
> 
> 
> Fam Zheng (3):
>   Revert "block: Fix unaligned zero write"
>   block: Fix NULL deference for unaligned write if qiov is NULL
>   qemu-iotests: Test unaligned sub-block zero write
> 
>  block.c                    | 123 +++++++++++++++++++++++++--------------------
>  tests/qemu-iotests/033     |  13 +++++
>  tests/qemu-iotests/033.out |  30 +++++++++++
>  3 files changed, 111 insertions(+), 55 deletions(-)
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>