Medium [CVE-2026-53095] Fix abuse of kprobe_write_ctx via freplace

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix abuse of kprobe_write_ctx via freplace uprobe programs are allowed to modify struct pt_regs. Since the actual program type of uprobe is KPROBE, it can be abused to modify struct pt_regs via kprobe+freplace when the kprobe attaches to kernel functions.

For example, SEC("?kprobe") int kprobe(struct pt_regs *regs) { return 0; } SEC("?freplace") int freplace_kprobe(struct pt_regs *regs) { regs->di = 0; return 0; } freplace_kprobe prog will attach to kprobe prog. kprobe prog will attach to a kernel function.

Without this patch, when the kernel function runs, its first arg will always be set as 0 via the freplace_kprobe prog. To fix the abuse of kprobe_write_ctx=true via kprobe+freplace, disallow attaching freplace programs on kprobe programs with different kprobe_write_ctx values.

This vulnerability allows for the abuse of the `kprobe_write_ctx` mechanism through `freplace` in Berkeley Packet Filter (BPF) kprobe programs. A local attacker could exploit this by attaching a `freplace` program to a `kprobe` program that is attached to a kernel function.

This could lead to the modification of the kernel function's arguments, specifically setting the first argument to zero, potentially causing unexpected system behavior or impacting data integrity.