Re: [PATCH bpf-next 2/2] bpf: Check link_create parameter for multi_uprobe

[Tao Chen]

在 2025/4/1 19:03, Jiri Olsa 写道:
> On Mon, Mar 31, 2025 at 05:47:45PM +0800, Tao Chen wrote:
> > The target_fd and flags in link_create no used in multi_uprobe
> > , return -EINVAL if they assigned, keep it same as other link
> > attach apis.
> >
> > Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link")
> > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > ---
> >   kernel/trace/bpf_trace.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 2f206a2a2..f7ebf17e3 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -3385,6 +3385,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> >   	if (sizeof(u64) != sizeof(void *))
> >   		return -EOPNOTSUPP;
> >   
> > +	if (attr->link_create.target_fd || attr->link_create.flags)
> > +		return -EINVAL;
>
> I think the CI is failing because usdt code does uprobe multi detection
> with target_fd = -1 and it fails and perf-uprobe fallback will fail on
> not having enough file descriptors

Hi jiri

As you said, i found it, thanks.

static int probe_uprobe_multi_link(int token_fd)
{
        LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
                .expected_attach_type = BPF_TRACE_UPROBE_MULTI,
                .token_fd = token_fd,
                .prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
        );
        LIBBPF_OPTS(bpf_link_create_opts, link_opts);
        struct bpf_insn insns[] = {
                BPF_MOV64_IMM(BPF_REG_0, 0),
                BPF_EXIT_INSN(),
        };
        int prog_fd, link_fd, err;
        unsigned long offset = 0;

        prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
                                insns, ARRAY_SIZE(insns), &load_opts);
        if (prog_fd < 0)
                return -errno;

        /* Creating uprobe in '/' binary should fail with -EBADF. */
        link_opts.uprobe_multi.path = "/";
        link_opts.uprobe_multi.offsets = &offset;
        link_opts.uprobe_multi.cnt = 1;

        link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, 
&link_opts);

> but I think at this stage we will brake some user apps by introducing
> this check, link ebpf go library, which passes 0

So is it ok just check the flags?

> jirka
>
>
> > +
> >   	if (!is_uprobe_multi(prog))
> >   		return -EINVAL;
> >   
> > --
> > 2.43.0


--
Best Regards
Tao Chen