CVE-2023-52831

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

cpu/hotplug: Dont offline the last non-isolated CPU

If a system has isolated CPUs via the isolcpus= command line parameter, then an attempt to offline the last housekeeping CPU will result in a WARN_ON() when rebuilding the scheduler domains and a subsequent panic due to and unhandled empty CPU mas in partition_sched_domains_locked().

cpuset_hotplug_workfn() rebuild_sched_domains_locked() ndoms = generate_sched_domains(&doms, &attr); cpumask_and(doms[0], top_cpuset.effective_cpus, housekeeping_cpumask(HK_FLAG_DOMAIN));

Thus results in an empty CPU mask which triggers the warning and then the subsequent crash:

WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408 Call trace: build_sched_domains+0x120c/0x1408 partition_sched_domains_locked+0x234/0x880 rebuild_sched_domains_locked+0x37c/0x798 rebuild_sched_domains+0x30/0x58 cpuset_hotplug_workfn+0x2a8/0x930

Unable to handle kernel paging request at virtual address fffe80027ab37080 partition_sched_domains_locked+0x318/0x880 rebuild_sched_domains_locked+0x37c/0x798

Aside of the resulting crash, it does not make any sense to offline the last last housekeeping CPU.

Prevent this by masking out the non-housekeeping CPUs when selecting a target CPU for initiating the CPU unplug operation via the work queue.

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/3073f6df783d9d75f7f69f73e16c7ef85d6cfb63
• https://git.kernel.org/stable/c/335a47ed71e332c82339d1aec0c7f6caccfcda13
• https://git.kernel.org/stable/c/3410b702354702b500bde10e3cc1f9db8731d908
• https://git.kernel.org/stable/c/38685e2a0476127db766f81b1c06019ddc4c9ffa
• https://git.kernel.org/stable/c/3073f6df783d9d75f7f69f73e16c7ef85d6cfb63
• https://git.kernel.org/stable/c/335a47ed71e332c82339d1aec0c7f6caccfcda13
• https://git.kernel.org/stable/c/3410b702354702b500bde10e3cc1f9db8731d908
• https://git.kernel.org/stable/c/38685e2a0476127db766f81b1c06019ddc4c9ffa