On Wed, Dec 13, 2023 at 6:12 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Currently the __uprobe_register will return 0 (success) when called with
> negative offset. The reason is that the call to register_for_each_vma and
> then build_map_info won't return error for negative offset. They just won't
> do anything - no matching vma is found so there's no registered breakpoint
> for the uprobe.
>
> I don't think we can change the behaviour of __uprobe_register and fail
> for negative uprobe offset, because apps might depend on that already.
>
> But I think we can still make the change and check for it on bpf multi
> link syscall level.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 774cf476a892..0dbf8d9b3ace 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3397,6 +3397,11 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> goto error_free;
> }
>
> + if (uprobes[i].offset < 0) {
> + err = -EINVAL;
> + goto error_free;
> + }
> +
nit: We have 3 __get_user() here. How about we move __get_user(offset)
to the first
and check offset immediately after it? This will save us a few
__get_user() in the
error path.
Thanks,
Song
> uprobes[i].link = link;
>
> if (flags & BPF_F_UPROBE_MULTI_RETURN)
> --
> 2.43.0
>
>
