CVE-2026-72068posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()

Official 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/feb5c87c8514444ba891b75a5a3eae57c64edaf8
• https://git.kernel.org/stable/c/384628d6cdde0fcd76868606fad3ad8293100afb
• https://git.kernel.org/stable/c/1fafc4d9b411645eb34de43362b966dc8fb3e263
• https://git.kernel.org/stable/c/cff8281bacd2866767e6194c3079d33b6c5a74f4
• https://git.kernel.org/stable/c/edf6babb9edd2d3e19229ade339081f439d4f478
• https://git.kernel.org/stable/c/ea6a188ee805e841a0e242f14d15953e0dfa74bb
• https://git.kernel.org/stable/c/571e1f10b5996ba3e4dc63ea77de4aa309c384ce
• https://git.kernel.org/stable/c/26aff38fefb1d6cd87e22525f41cc8f1aa61b24f