Re: [External] Re: [PATCH] kprobes: Fix kill kprobe which has been marked as gone

[Muchun Song]

On Fri, Aug 21, 2020 at 9:28 PM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> On Fri, 21 Aug 2020 21:28:43 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> > Hi Muchun,
> >
> > On Thu, 20 Aug 2020 11:19:33 +0800
> > Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> >
> > > If a kprobe is marked as gone, we should not kill it again. Otherwise,
> > > we can disarm the kprobe more than once. In that case, the statistics
> > > of kprobe_ftrace_enabled can unbalance which can lead to that kprobe
> > > do not work.
> > >
> >
> > Good catch! Hmm, I think we also need an assertion in
> > kill_kprobe() so that p is already gone. Anyway, this looks good to me.
> >
> > Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> >
> > Thanks!
> >
> > > Fixes: 0cb2f1372baa ("kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler")
>
> BTW, this fixes older bug than this commit.
>
> Fixes: e8386a0cb22f ("kprobes: support probing module __exit function")

Yeah, it's right. Thanks.

>
> Thank you,
>
> > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > > Co-developed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> > > Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> > > ---
> > >  kernel/kprobes.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > > index d36e2b017588..7bac3ea44ff4 100644
> > > --- a/kernel/kprobes.c
> > > +++ b/kernel/kprobes.c
> > > @@ -2422,7 +2422,10 @@ static int kprobes_module_callback(struct notifier_block *nb,
> > >     mutex_lock(&kprobe_mutex);
> > >     for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> > >             head = &kprobe_table[i];
> > > -           hlist_for_each_entry(p, head, hlist)
> > > +           hlist_for_each_entry(p, head, hlist) {
> > > +                   if (kprobe_gone(p))
> > > +                           continue;
> > > +
> > >                     if (within_module_init((unsigned long)p->addr, mod) ||
> > >                         (checkcore &&
> > >                          within_module_core((unsigned long)p->addr, mod))) {
> > > @@ -2439,6 +2442,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
> > >                              */
> > >                             kill_kprobe(p);
> > >                     }
> > > +           }
> > >     }
> > >     if (val == MODULE_STATE_GOING)
> > >             remove_module_kprobe_blacklist(mod);
> > > --
> > > 2.11.0
> > >
> >
> >
> > --
> > Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>
>
> --
> Masami Hiramatsu <mhiramat@xxxxxxxxxx>



-- 
Yours,
Muchun