Re: [PATCHv2 mm-stable] uprobes: Revert ref_ctr_offset in uprobe_unregister error path

[David Hildenbrand]

On 17.06.25 13:58, Jiri Olsa wrote:
> ping
>
> On Wed, Jun 11, 2025 at 10:57:08AM +0200, Jiri Olsa wrote:
> > hi, ping ;-)
> >
> > On Wed, Jun 04, 2025 at 10:28:42PM +0200, Jiri Olsa wrote:
> > > On Wed, May 14, 2025 at 12:18:09PM +0200, Jiri Olsa wrote:
> > > > From: Jiri Olsa <olsajiri@xxxxxxxxx>
> > > >
> > > > There's error path that could lead to inactive uprobe:
> > > >
> > > >    1) uprobe_register succeeds - updates instruction to int3 and
> > > >       changes ref_ctr from 0 to 1
> > > >    2) uprobe_unregister fails  - int3 stays in place, but ref_ctr
> > > >       is changed to 0 (it's not restored to 1 in the fail path)
> > > >       uprobe is leaked
> > > >    3) another uprobe_register comes and re-uses the leaked uprobe
> > > >       and succeds - but int3 is already in place, so ref_ctr update
> > > >       is skipped and it stays 0 - uprobe CAN NOT be triggered now
> > > >    4) uprobe_unregister fails because ref_ctr value is unexpected
> > > >
> > > > Fixing this by reverting the updated ref_ctr value back to 1 in step 2),
> > > > which is the case when uprobe_unregister fails (int3 stays in place),
> > > > but we have already updated refctr.
> > > >
> > > > The new scenario will go as follows:
> > > >
> > > >    1) uprobe_register succeeds - updates instruction to int3 and
> > > >       changes ref_ctr from 0 to 1
> > > >    2) uprobe_unregister fails  - int3 stays in place and ref_ctr
> > > >       is reverted to 1..  uprobe is leaked
> > > >    3) another uprobe_register comes and re-uses the leaked uprobe
> > > >       and succeds - but int3 is already in place, so ref_ctr update
> > > >       is skipped and it stays 1 - uprobe CAN be triggered now
> > > >    4) uprobe_unregister succeeds
> > > >
> > > > Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
> > > > Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> > > > Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> > > > Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> > > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > >
> > > hi,
> > > I can't find this in any related tree, was this pulled in?

@Andrew, I assume you should pick this.

--
Cheers,

David / dhildenb