[PATCH 5/7] kprobes: Do not try to disarm already disarmed Kprobe

Petr Mladek
2015-02-26T16:14:27Z

The global kprobes_all_disarmed flag says that all Kprobes are disarmed
even when they are marked as enabled. This is properly handled in
register_kprobe() but it is ignored in __disable_kprobe().

This problem gets more serious after we started handling errors from
disarm_kprobe(). The second disarming fails and we do not longer
set KPROBE_FLAG_DISABLED. It might trigger BUG_ON(!kprobe_disarmed(ap))
in __unregister_kprobe_top() even when Kprobes were globally
disarmed.

Well, kprobe_disarmed(ap) should return false when the global
kprobes_all_disarmed flag is set. But let's solve this separately.

This patch fixes __disable_kprobe(), so that it does not disarm
when the Kprobe is not armed.

Note that I reverted the condition "if (kprobe_disabled(p))" and used "goto
out" there. It helped to keep the code nesting on a reasonable level.

Signed-off-by: Petr Mladek <pmladek@suse.cz>
---
kernel/kprobes.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 1fcb19095b43..54bc2a6960b4 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1594,22 +1594,25 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
if (unlikely(orig_p == NULL))
return ERR_PTR(-EINVAL);

- if (!kprobe_disabled(p)) {
- /* Disable probe if it is a child probe */
- if (p != orig_p)
- p->flags |= KPROBE_FLAG_DISABLED;
+ if (kprobe_disabled(p))
+ goto out;
+
+ /* Disable probe if it is a child probe */
+ if (p != orig_p)
+ p->flags |= KPROBE_FLAG_DISABLED;

- /* Try to disarm and disable this/parent probe */
- if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
+ /* Try to disarm and disable this/parent probe */
+ if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
+ if (!kprobes_all_disarmed) {
err = disarm_kprobe(orig_p, true);
if (err) {
p->flags &= ~KPROBE_FLAG_DISABLED;
return ERR_PTR(err);
}
- orig_p->flags |= KPROBE_FLAG_DISABLED;
}
+ orig_p->flags |= KPROBE_FLAG_DISABLED;
}
-
+out:
return orig_p;
}

--
1.8.5.6