vdpa_sim_blk: reject out-of-range sector starts

vdpasim_blk_check_range() logs an invalid start sector but continues
validating the request.  The subsequent unsigned capacity subtraction can
underflow and let an out-of-range buffer offset reach the data path.

The invalid offset is used by three request paths.  VIRTIO_BLK_T_OUT
copies guest data to blk->buffer + offset through
vringh_iov_pull_iotlb(), causing an out-of-bounds write in
_copy_from_iter() or memcpy().  VIRTIO_BLK_T_IN copies from
blk->buffer + offset to the guest through vringh_iov_push_iotlb(),
causing an out-of-bounds read in _copy_to_iter().
VIRTIO_BLK_T_WRITE_ZEROES passes blk->buffer + offset to memset(),
causing an out-of-bounds write.

Reject starts at or beyond the capacity before the subtraction.  Treat the
capacity boundary as invalid because the IN and OUT paths round byte counts
down to sectors for validation but later copy the original byte counts.  A
sub-sector request at the capacity boundary would otherwise still access
past the end of the buffer.

I found this bug myself, though the patch was written with AI assistance.

Fixes: 7d189f617f83 ("vdpa_sim_blk: implement ramdisk behaviour")
Assisted-by: OpenAI-Codex:GPT-5
Signed-off-by: Linfeng Sun <linfeng.sun.dev@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260901094800.25475-1-linfeng.sun.dev@gmail.com>

0 files changed, 0 insertions, 0 deletions