CVE-2026-72068
Description
In the Linux kernel, the following vulnerability has been resolved:
posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()
update_rlimit_cpu() converts the RLIMIT_CPU value to nanoseconds with
u64 nsecs = rlim_new * NSEC_PER_SEC;
On 32-bit kernels both rlim_new (unsigned long) and NSEC_PER_SEC
(1000000000L) are 32-bit, so the multiplication is performed in unsigned
long and truncated for rlim_new > 4 seconds before being widened to u64.
The same file already casts to u64 for the matching computation in
check_process_timers():
u64 softns = (u64)soft * NSEC_PER_SEC;
As a result, the truncated value is installed into the CPUCLOCK_PROF
expiry cache (nextevt), causing the process CPU timer to be programmed
to fire prematurely for any RLIMIT_CPU soft limit >= 5 seconds. The
actual SIGXCPU/SIGKILL decision in check_process_timers() already casts
to u64 and is therefore correct, so limit enforcement is not broken;
only the expiry-cache programming is wrong. Apply the same cast here so
both paths convert rlim_cur identically.
64-bit kernels are unaffected.