linux-kernel - [PATCH] powerpc/prom: fix use-after-free on cpu_to_chip

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Date:   Fri, 5 Jul 2019 17:01:00 +0800
From:   Wen Yang <wen.yang99@....com.cn>
To:     linux-kernel@...r.kernel.org
Cc:     xue.zhihong@....com.cn, wang.yi59@....com.cn,
        cheng.shengyu@....com.cn, Wen Yang <wen.yang99@....com.cn>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/prom: fix use-after-free on cpu_to_chip_id()

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@....com.cn>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Christophe Leroy <christophe.leroy@....fr>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-kernel@...r.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