[PATCH] kprobes: fix a memory leak in function pre_handler_kretprobe()

[Jiang Liu <liuj97@gmail.com>]

In function pre_handler_kretprobe(), the allocated kretprobe_instance object
will get leaked if the entry_handler callback returns non-zero. This may cause
all the preallocated kretprobe_instance objects exhausted. This issue could be
reproduced by changing samples/kprobes/kretprobe_example.c to probe
"mutex_unlock". And the fix is straight forward, just put the allocated
kretprobe_instance object back onto the free_instances list.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Jim Keniston <jkenisto@us.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
CC: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
CC: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: stable@vger.kernel.org
---
 kernel/kprobes.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index e5d8464..2423295 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1673,8 +1673,12 @@ static int __kprobes pre_handler_kretprobe(struct kprobe *p,
 		ri->rp = rp;
 		ri->task = current;
 
-		if (rp->entry_handler && rp->entry_handler(ri, regs))
+		if (rp->entry_handler && rp->entry_handler(ri, regs)) {
+			spin_lock_irqsave(&rp->lock, flags);
+			hlist_add_head(&ri->hlist, &rp->free_instances);
+			spin_unlock_irqrestore(&rp->lock, flags);
 			return 0;
+		}
 
 		arch_prepare_kretprobe(ri, regs);
 
-- 
1.7.5.4