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

cifs: remove all cifs files before kill super

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

BUG: kernel NULL pointer dereference, address: 0000000000000000 ... [ 134.222152] listlruadd+0x64/0x1a0 [ 134.222399] ? cifsputtcon+0x171/0x340 [cifs] [ 134.222772] dlruadd+0x44/0x60 [ 134.222997] dput+0x1fc/0x210 [ 134.223213] cifsFileInfoputfinal+0x11a/0x140 [cifs] [ 134.223576] processonework+0x17c/0x320 [ 134.223843] workerthread+0x188/0x280 [ 134.224084] ? pfxworkerthread+0x10/0x10 [ 134.224366] kthread+0xcc/0x100 [ 134.224576] ? pfxkthread+0x10/0x10 [ 134.224827] retfromfork+0x30/0x50 [ 134.225063] ? pfxkthread+0x10/0x10 [ 134.225328] retfromforkasm+0x1b/0x30

This can be reproduce by following: unshare -n bash -c " mkdir -p ${CIFSMNT} 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.ipforward=1 ip netns exec root iptables -t nat -A POSTROUTING -s 192.168.0.2 -o ${DEV} -j MASQUERADE mount -t cifs ${CIFSPATH} ${CIFSMNT} -o vers=3.0,sec=ntlmssp,credentials=${CIFSCRED},rsize=65536,wsize=65536,cache=none,echointerval=1 touch ${CIFSMNT}/a.txt ip netns exec root iptables -t nat -D POSTROUTING -s 192.168.0.2 -o ${DEV} -j MASQUERADE " umount ${CIFSMNT}