[BUGFIX] kprobes: prevent re-registration of the same kprobe

[Ananth N Mavinakayanahalli <ananth@in.ibm.com>]

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...

---
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);