In the Linux kernel, the following vulnerability has been resolved:
cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed
Creating a child cpuset where cpuset.mems is never set leads to a div/0 when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a CPU hotplug event.
Reproduction steps:
- Create a cgroup w/ cpuset controls (do not set cpuset.mems)
- Move the task into the child cpuset
- Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES
- unplug and hotplug a cpu echo 0 > /sys/devices/system/cpu/cpu1/online echo 1 > /sys/devices/system/cpu/cpu1/online
- mempolicy rebind does a div/0 in mpol_relative_nodemask on the call to __nodes_fold()
The cpuset code passes (cs->mems_allowed) which is not guaranteed to have nodes to the rebind routine. Use cs->effective_mems instead, which is guaranteed to have a non-empty nodemask once we reach that code path.
[ david: add a comment, slightly rephrase description ]
References
- https://git.kernel.org/stable/c/02f67c4f88be8e3dbd91951d13cdcc5bcc82e9c7
- https://git.kernel.org/stable/c/4b06449384b9ee5b3372bab60601ba5cd4162086
- https://git.kernel.org/stable/c/b7adeba2a21c98c7b20f18e27e3ead86bdb5e08d
- https://git.kernel.org/stable/c/b983c56426383e4a06fa5970c4e33cee879b1482
- https://git.kernel.org/stable/c/c17f06d8a085d6be58b544a440ce243f5e441a60
- https://git.kernel.org/stable/c/c844b7d9a9586de15dd28c06da5cc7f6ab28787d
- https://git.kernel.org/stable/c/fc680afc510157f6b137956011c09abc23eb0842
- https://git.kernel.org/stable/c/fcc8c310539c3cc523419113b227161a96b50550