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

[Jiang Liu]

From: Jiang Liu <liuj97@xxxxxxxxx>

In function pre_handler_kretprobe(), the allocated kretprobe_instance object
will be 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@xxxxxxxxxx>
Acked-by: Jim Keniston <jkenisto@xxxxxxxxxx>
Acked-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
---
 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

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