On 5/15/23 11:14 PM, Song Liu wrote:
On May 15, 2023, at 1:17 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
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.
I am not following. If modify_fentry() fails, we will not use the new
image anywhere, no? Did I miss something?
Hm, agree, I think I got confused with the again label earlier. Looks ok
indeed. Applied, thanks!
