[PATCH] kretprobe: check re-registration of the same kretprobe earlier

[Cheng Jian]

Our system encountered a use-after-free when re-register a
same kretprobe. it access the hlist node in rp->free_instances
which has been released already.

Prevent re-registration has been implemented for kprobe before,
but it's too late for kretprobe. We must check the re-registration
before re-initializing the kretprobe, otherwise it will destroy the
data and struct of the kretprobe registered, it can lead to memory
leak and use-after-free.

Signed-off-by: Cheng Jian <cj.chengjian@xxxxxxxxxx>
---
 kernel/kprobes.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2625c24..f1fc921 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1946,6 +1946,11 @@ int register_kretprobe(struct kretprobe *rp)
 		}
 	}
 
+	/* Return error if it's being re-registered */
+	ret = check_kprobe_rereg(&rp->kp);
+	if (ret)
+		return ret;
+
 	rp->kp.pre_handler = pre_handler_kretprobe;
 	rp->kp.post_handler = NULL;
 	rp->kp.fault_handler = NULL;
-- 
2.7.4