[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.yang99@xxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Christophe Leroy <christophe.leroy@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 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