From d0a72efac89d1c35ac55197895201b7b94c5e6ef Mon Sep 17 00:00:00 2001
From: Oliver O'Halloran <oohall@gmail.com>
Date: Thu, 6 Feb 2020 17:26:21 +1100
Subject: [PATCH] cpufreq: powernv: Fix use-after-free

References: bsc#1065729
Patch-mainline: v5.7-rc1
Git-commit: d0a72efac89d1c35ac55197895201b7b94c5e6ef

The cpufreq driver has a use-after-free that we can hit if:

a) There's an OCC message pending when the notifier is registered, and
b) The cpufreq driver fails to register with the core.

When a) occurs the notifier schedules a workqueue item to handle the
message. The backing work_struct is located on chips[].throttle and
when b) happens we clean up by freeing the array. Once we get to
the (now free) queued item and the kernel crashes.

Fixes: c5e29ea7ac14 ("cpufreq: powernv: Fix bugs in powernv_cpufreq_{init/exit}")
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200206062622.28235-1-oohall@gmail.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 drivers/cpufreq/powernv-cpufreq.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 56f4bc0d209e..1806b1da4366 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -1080,6 +1080,12 @@ static int init_chip_info(void)
 
 static inline void clean_chip_info(void)
 {
+	int i;
+
+	/* flush any pending work items */
+	if (chips)
+		for (i = 0; i < nr_chips; i++)
+			cancel_work_sync(&chips[i].throttle);
 	kfree(chips);
 }
 
-- 
2.23.0