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 <[email protected]>
> >
> > 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 <[email protected]>
> > Acked-by: Oleg Nesterov <[email protected]>
> > Suggested-by: Oleg Nesterov <[email protected]>
> > Signed-off-by: Jiri Olsa <[email protected]>
>
> hi,
> I can't find this in any related tree, was this pulled in?
>
> thanks,
> jirka
>
>
> > ---
> > v2 changes:
> > - adding proper Fixes tag and acks
> >
> > kernel/events/uprobes.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 4c965ba77f9f..84ee7b590861 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -581,8 +581,8 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe,
> > struct vm_area_struct *vma,
> >
> > out:
> > /* Revert back reference counter if instruction update failed. */
> > - if (ret < 0 && is_register && ref_ctr_updated)
> > - update_ref_ctr(uprobe, mm, -1);
> > + if (ret < 0 && ref_ctr_updated)
> > + update_ref_ctr(uprobe, mm, is_register ? -1 : 1);
> >
> > /* try collapse pmd for compound page */
> > if (ret > 0)
> > --
> > 2.49.0
> >
