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

cifs: remove all cifs files before kill super

Cifs files may be put into fileinfo_put_wq during umounting cifs.
After umount done, cifsFileInfo_put_final is called, which cause
following BUG:

BUG: kernel NULL pointer dereference, address: 0000000000000000
...
[ 134.222152] list_lru_add+0x64/0x1a0
[ 134.222399] ? cifs_put_tcon+0x171/0x340 [cifs]
[ 134.222772] d_lru_add+0x44/0x60
[ 134.222997] dput+0x1fc/0x210
[ 134.223213] cifsFileInfo_put_final+0x11a/0x140 [cifs]
[ 134.223576] process_one_work+0x17c/0x320
[ 134.223843] worker_thread+0x188/0x280
[ 134.224084] ? __pfx_worker_thread+0x10/0x10
[ 134.224366] kthread+0xcc/0x100
[ 134.224576] ? __pfx_kthread+0x10/0x10
[ 134.224827] ret_from_fork+0x30/0x50
[ 134.225063] ? __pfx_kthread+0x10/0x10
[ 134.225328] ret_from_fork_asm+0x1b/0x30

This can be reproduce by following:
unshare -n bash -c "
mkdir -p ${CIFS_MNT}
ip netns attach root 1
ip link add eth0 type veth peer veth0 netns root
ip link set eth0 up
ip -n root link set veth0 up
ip addr add 192.168.0.2/24 dev eth0
ip -n root addr add 192.168.0.1/24 dev veth0
ip route add default via 192.168.0.1 dev eth0
ip netns exec root sysctl net.ipv4.ip_forward=1
ip netns exec root iptables -t nat -A POSTROUTING -s 192.168.0.2 -o
${DEV} -j MASQUERADE
mount -t cifs ${CIFS_PATH} ${CIFS_MNT} -o
vers=3.0,sec=ntlmssp,credentials=${CIFS_CRED},rsize=65536,wsize=65536,cache=none,echo_interval=1
touch ${CIFS_MNT}/a.txt
ip netns exec root iptables -t nat -D POSTROUTING -s 192.168.0.2 -o
${DEV} -j MASQUERADE
"
umount ${CIFS_MNT}