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

[Masami Hiramatsu]

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")

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>