CVE-2026-53187

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

RDMA/core: Validate cpu_id against nr_cpu_ids in DMAH alloc

The cpu_id attribute supplied by user space through UVERBS_ATTR_ALLOC_DMAH_CPU_ID is passed directly to cpumask_test_cpu() without first verifying that the value is within the valid CPU range.

Passing such untrusted data to cpumask_test_cpu() may lead to an out-of-bounds read of the underlying cpumask bitmap: the helper expands to a test_bit() that indexes the bitmap by cpu_id / BITS_PER_LONG with no bound check.

In addition, on kernels built with CONFIG_DEBUG_PER_CPU_MAPS it trips the WARN_ON_ONCE() in cpumask_check(); combined with panic_on_warn this turns a bad user input into a machine reboot.

Reject any cpu_id that is not smaller than nr_cpu_ids with -EINVAL before it is used.

Reported by Smatch.