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

[Tao Chen <chen.dylane@linux.dev>]

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@linux.dev>
>> ---
>>   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