[Qemu-devel] [PATCH v2 0/2] block: Fix unaligned bdrv_aio_write_zeroes

[Fam Zheng <famz@redhat.com>]

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.

v2: Split to three aligned pwritev.

Fam Zheng (2):
  Revert "block: Fix unaligned zero write"
  block: Fix NULL deference for unaligned write if qiov is NULL

 block.c | 121 +++++++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 66 insertions(+), 55 deletions(-)

-- 
1.9.3