Messages in this thread | | | Date | Sun, 13 Sep 2009 21:47:39 -0400 | From | Masami Hiramatsu <> | Subject | Re: [BUGFIX] kprobes: prevent re-registration of the same kprobe |
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Ananth N Mavinakayanahalli wrote: > On Fri, Sep 11, 2009 at 05:12:54AM +0200, Frederic Weisbecker wrote: >> On Thu, Sep 10, 2009 at 07:53:30PM -0400, Masami Hiramatsu wrote: > > ... > >> Is it possible to have two kprobes having the exact same >> properties? (pointing to the same address, having the same >> probe handlers, etc...) > > Yes, this is possible with two *different* kprobes. However, we have a bug > with the current code where there is insufficient scaffolding to prevent > re-registration of the same kprobe. Here is a patch...
Indeed, that is a bug, or spec. I didn't expect that user register same kprobes twice.
> --- > Prevent re-registration of the same kprobe. Current code allows this, > albeit with disastrous consequences. Its not a common case, but should > be flagged nonetheless. > > Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com> > --- > kernel/kprobes.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: ptrace-10sep/kernel/kprobes.c > =================================================================== > --- ptrace-10sep.orig/kernel/kprobes.c > +++ ptrace-10sep/kernel/kprobes.c > @@ -589,6 +589,9 @@ static int __kprobes register_aggr_kprob > int ret = 0; > struct kprobe *ap = old_p; > > + if (old_p == p) > + /* Attempt to re-register the same kprobe.. fail */ > + return -EINVAL; > if (old_p->pre_handler != aggr_pre_handler) { > /* If old_p is not an aggr_probe, create new aggr_kprobe. */ > ap = kzalloc(sizeof(struct kprobe), GFP_KERNEL);
Hmm, if we catch the second registration here, it's too late. At register_kprobe(), we initialized some field of kprobe before calling register_aggr_kprobe(). Especially kprobe.list is cleared.
And this can't check the case that 'p' is already registered on an aggr kprobe.
Thus, I think some initialization paths should be changed (kp.flag field is initialized too early, yearh, that's my mistake), and also, you will need to use get_valid_kprobe() to check the kprobe has not been registered.
Thank you,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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