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

[Jiang Liu <liuj97@gmail.com>]

From: Jiang Liu<liuj97@gmail.com>

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<liuj97@gmail.com>
Cc: Hien Nguyen<hien@us.ibm.com>
Cc: Jim Keniston<jkenisto@us.ibm.com>
Cc: Prasanna S Panchamukhi<prasanna@in.ibm.com>
---
  kprobes.c |    6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1660,8 +1660,12 @@
                 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);