Re: [PATCH] uprobes: Fix NULL pointer dereference in hprobe_expire()

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On Wed, 29 Jul 2026 12:31:08 -0700
Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:

> On Wed, Jul 29, 2026 at 9:02 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > On 07/29, Breno Leitao wrote:
> > >
> > > --- a/kernel/events/uprobes.c
> > > +++ b/kernel/events/uprobes.c
> > > @@ -832,7 +832,7 @@ static struct uprobe *hprobe_expire(struct hprobe *hprobe, bool get)
> > >               if (try_cmpxchg(&hprobe->state, &hstate, uprobe ? HPROBE_STABLE : HPROBE_GONE)) {
> > >                       /* We won the race, we are the ones to unlock SRCU */
> > >                       __srcu_read_unlock(&uretprobes_srcu, hprobe->srcu_idx);
> > > -                     return get ? get_uprobe(uprobe) : uprobe;
> > > +                     return get && uprobe ? get_uprobe(uprobe) : uprobe;
> >
> > Well, looks "obviously correct". At least the current code is obviously
> > wrong, it even checks uprobe != NULL 3 lines above.
> >
> > Andrii ?
> >
> 
> Yes, indeed, I'm more surprised this didn't come up much earlier
> (probably it's rare enough to have uretprobe with refcnt at zero
> during fork). The fix looks good, thanks!
> 
> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> 
> > Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> >

Thanks, this seems good to me. (uprobe is NULL checked in try_cmpxchg(),
so it could be NULL.)

Can I pick this to probes/fixes branch?

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>