On Tue, Jun 13, 2023 at 4:31 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> We currently allow to create perf link for program with
> expected_attach_type == BPF_TRACE_KPROBE_MULTI.
>
> This will cause crash when we call helpers like get_attach_cookie or
> get_func_ip in such program, because it will call the kprobe_multi's
> version (current->bpf_ctx context setup) of those helpers while it
> expects perf_link's current->bpf_ctx context setup.
>
> Making sure that we use BPF_TRACE_KPROBE_MULTI expected_attach_type
> only for programs attaching through kprobe_multi link.
>
> Fixes: ca74823c6e16 ("bpf: Add cookie support to programs attached with kprobe multi link")
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> kernel/bpf/syscall.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 0c21d0d8efe4..e8fe04a5db93 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4675,6 +4675,11 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
> ret = bpf_perf_link_attach(attr, prog);
> break;
> case BPF_PROG_TYPE_KPROBE:
> + if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI &&
> + attr->link_create.attach_type != BPF_TRACE_KPROBE_MULTI) {
> + ret = -EINVAL;
> + goto out;
> + }
there is a separate expected attach type validation switch above this,
shouldn't this go there? We also have
bpf_prog_attach_check_attach_type() call above as well, and tbh by now
I'm not sure why we have like three places to check conditions like
this... But I'd put this check in either
bpf_prog_attach_check_attach_type() or in the dedicated switch for
attach_type checks.
> if (attr->link_create.attach_type == BPF_PERF_EVENT)
> ret = bpf_perf_link_attach(attr, prog);
> else
> --
> 2.40.1
>
