On Thu, Dec 14, 2023 at 1:07 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Wed, Dec 13, 2023 at 03:43:04PM -0800, Andrii Nakryiko wrote:
> > 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) {
> >
> > offset in UAPI is defined as unsigned, so how can it be negative?
>
> right, but then it's passed to uprobe_register_refctr as loff_t which is 'long long'
ah, so it's not rejected because uprobe_register expects signed offset
(for some reason...) and it only does
if (offset > i_size_read(inode))
got it, thanks.
>
> jirka
>
> >
> > > + err = -EINVAL;
> > > + goto error_free;
> > > + }
> > > +
> > > uprobes[i].link = link;
> > >
> > > if (flags & BPF_F_UPROBE_MULTI_RETURN)
> > > --
> > > 2.43.0
> > >
