ceph: supply snapshot context in ceph_zero_partial_object()

In the Linux kernel, the following vulnerability has been resolved:

ceph: supply snapshot context in ceph_zero_partial_object()

The ceph_zero_partial_object function was missing proper snapshot

context for its OSD write operations, which could lead to data

inconsistencies in snapshots.

Reproducer:

../src/vstart.sh --new -x --localhost --bluestore

./bin/ceph auth caps client.fs_a mds 'allow rwps fsname=a' mon 'allow r fsname=a' osd 'allow rw tag cephfs data=a'

mount -t ceph [email protected]=/ /mnt/mycephfs/ -o conf=./ceph.conf

dd if=/dev/urandom of=/mnt/mycephfs/foo bs=64K count=1

mkdir /mnt/mycephfs/.snap/snap1

md5sum /mnt/mycephfs/.snap/snap1/foo

fallocate -p -o 0 -l 4096 /mnt/mycephfs/foo

echo 3 > /proc/sys/vm/drop/caches

md5sum /mnt/mycephfs/.snap/snap1/foo # get different md5sum!!