CVE-2026-97420

In the Linux kernel, the following vulnerability has been resolved: bpf: NUL-terminate replaced sysctl value When writing to sysctls, proc_sys_call_handler() guarantees that the buffer passed to proc handlers is NUL-terminated. If bpf_sysctl_set_new_value() replaces the pending sysctl value, it can hand a replacement buffer directly to proc handlers. However, the helper currently copies only buf_len bytes into that buffer without appending a NUL terminator, leaving downstream parsers vulnerable to out-of-bounds access. Fix this by appending a '\0' after the replaced value to restore the expected sysctl semantics. Since the helper already rejects buf_len greater than PAGE_SIZE - 1, there is always room for the extra byte. Reproduced in a QEMU x86_64 guest booted with KASAN while exercising the sysctl replacement path with a cgroup/sysctl BPF program. The reproducer targets `/proc/sys/net/core/flow_limit_cpu_bitmap`, fills the original user write buffer with non-zero bytes, and overrides the sysctl value so the replacement buffer lacks a terminating NUL. Under that setup, the pre-fix kernel reported: BUG: KASAN: slab-out-of-bounds in strnchrnul+0x72/0x90 Read of size 1 at addr ffff88