[PATCH] powerpc/prom: fix use-after-free on cpu_to_chip_id()

[Wen Yang]

The np variable is still being used after the of_node_put() call,
which may result in use-after-free.
We fix this issue by calling of_node_put() after the last usage.

Fixes: 3eb906c6b6c1 ("powerpc: Make cpu_to_chip_id() available when SMP=n")
Signed-off-by: Wen Yang <wen.yan...@zte.com.cn>
Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Christophe Leroy <christophe.le...@c-s.fr>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Mike Rapoport <r...@linux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: "Aneesh Kumar K.V" <aneesh.ku...@linux.ibm.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-ker...@vger.kernel.org
---
 arch/powerpc/kernel/prom.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 7159e79..ad87b94 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -872,13 +872,15 @@ EXPORT_SYMBOL(of_get_ibm_chip_id);
 int cpu_to_chip_id(int cpu)
 {
        struct device_node *np;
+       int id;
 
        np = of_get_cpu_node(cpu, NULL);
        if (!np)
                return -1;
 
+       id = of_get_ibm_chip_id(np);
        of_node_put(np);
-       return of_get_ibm_chip_id(np);
+       return id;
 }
 EXPORT_SYMBOL(cpu_to_chip_id);
 
-- 
2.9.5