On 5/15/23 5:52 PM, Song Liu wrote:
On Mon, May 15, 2023 at 6:09 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:If it fails to attach fentry, the allocated bpf trampoline image will be left in the system. That can be verified by checking /proc/kallsyms. This meamleak can be verified by a simple bpf program as follows, SEC("fentry/trap_init") int fentry_run() { return 0; } It will fail to attach trap_init because this function is freed after kernel init, and then we can find the trampoline image is left in the system by checking /proc/kallsyms. $ tail /proc/kallsyms ffffffffc0613000 t bpf_trampoline_6442453466_1 [bpf] ffffffffc06c3000 t bpf_trampoline_6442453466_1 [bpf] $ bpftool btf dump file /sys/kernel/btf/vmlinux | grep "FUNC 'trap_init'" [2522] FUNC 'trap_init' type_id=119 linkage=static $ echo $((6442453466 & 0x7fffffff)) 2522 Note that there are two left bpf trampoline images, that is because the libbpf will fallback to raw tracepoint if -EINVAL is returned. Fixes: e21aa341785c ("bpf: Fix fexit trampoline.") Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Cc: Song Liu <song@xxxxxxxxxx> Cc: Jiri Olsa <olsajiri@xxxxxxxxx>Acked-by: Song Liu <song@xxxxxxxxxx>
Won't this trigger a UAF for the case when progs are already running at this address aka modify_fentry() fails where you would then also hit the goto out_free path? This looks not correct to me. Thanks, Daniel
