lkml.org 
[lkml]   [2009]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [BUGFIX] kprobes: prevent re-registration of the same kprobe
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



\
 
 \ /
  Last update: 2009-09-14 03:49    [W:1.764 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site