linux-kernel - [PATCH] cpufreq: fix overflow in cpufreq_table_find_index

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Message-Id: <20161017151456.3573-1-sergey.senozhatsky@gmail.com>
Date:   Tue, 18 Oct 2016 00:14:56 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Aaro Koskinen <aaro.koskinen@....fi>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [PATCH] cpufreq: fix overflow in cpufreq_table_find_index_dl()

'best' is always less or equals to 'pos', so `best - pos' returns
a negative value which is then getting casted to `unsigned int'
and passed to __cpufreq_driver_target()->acpi_cpufreq_target()
for policy->freq_table election. This results in:

 BUG: unable to handle kernel paging request at ffff881019b469f8
 IP: [<ffffffffa00356c1>] acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
 PGD 267f067
 PUD 0

 Oops: 0000 [#1] PREEMPT SMP
 CPU: 6 PID: 70 Comm: kworker/6:1 Not tainted 4.9.0-rc1-next-20161017
 Workqueue: events dbs_work_handler
 task: ffff88041b808000 task.stack: ffff88041b810000
 RIP: 0010:[<ffffffffa00356c1>]  [<ffffffffa00356c1>] acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
 RSP: 0018:ffff88041b813c60  EFLAGS: 00010282
 RAX: ffff880419b46a00 RBX: ffff88041b848400 RCX: ffff880419b20f80
 RDX: 00000000001dff38 RSI: 00000000ffffffff RDI: ffff88041b848400
 RBP: ffff88041b813cb0 R08: 0000000000000006 R09: 0000000000000040
 R10: ffffffff8207f9e0 R11: ffffffff8173595b R12: 0000000000000000
 R13: ffff88041f1dff38 R14: 0000000000262900 R15: 0000000bfffffff4
 FS:  0000000000000000(0000) GS:ffff88041f000000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffff881019b469f8 CR3: 000000041a2d3000 CR4: 00000000001406e0
 Stack:
  ffff88041b813cb0 ffffffff813347f9 ffff88041b813ca0 ffffffff81334663
  ffff88041f1d4bc0 ffff88041b848400 0000000000000000 0000000000000000
  0000000000262900 0000000000000000 ffff88041b813d00 ffffffff813355dc
 Call Trace:
  [<ffffffff813347f9>] ? cpufreq_freq_transition_begin+0xf1/0xfc
  [<ffffffff81334663>] ? get_cpu_idle_time+0x97/0xa6
  [<ffffffff813355dc>] __cpufreq_driver_target+0x3b6/0x44e
  [<ffffffff81336ca3>] cs_dbs_timer+0x11a/0x135
  [<ffffffff81336fda>] dbs_work_handler+0x39/0x62
  [<ffffffff81057823>] process_one_work+0x280/0x4a5
  [<ffffffff81058719>] worker_thread+0x24f/0x397
  [<ffffffff810584ca>] ? rescuer_thread+0x30b/0x30b
  [<ffffffff81418380>] ? nl80211_get_key+0x29/0x36a
  [<ffffffff8105d2b7>] kthread+0xfc/0x104
  [<ffffffff8107ceea>] ? put_lock_stats.isra.9+0xe/0x20
  [<ffffffff8105d1bb>] ? kthread_create_on_node+0x3f/0x3f
  [<ffffffff814b2092>] ret_from_fork+0x22/0x30
 Code: 56 4d 6b ff 0c 41 55 41 54 53 48 83 ec 28 48 8b 15 ad 1e 00 00 44 8b 41
 08 48 8b 87 c8 00 00 00 49 89 d5 4e 03 2c c5 80 b2 78 81 <46> 8b 74 38 04 45
 3b 75 00 75 11 31 c0 83 39 00 0f 84 1c 01 00
 RIP  [<ffffffffa00356c1>] acpi_cpufreq_target+0x4f/0x190 [acpi_cpufreq]
  RSP <ffff88041b813c60>
 CR2: ffff881019b469f8
 ---[ end trace 16d9fc7a17897d37 ]---

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 include/linux/cpufreq.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 5fa55fc..2a7aa0b 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -677,10 +677,10 @@ static inline int cpufreq_table_find_index_dl(struct cpufreq_policy *policy,
 		if (best == table - 1)
 			return pos - table;
 
-		return best - pos;
+		return pos - best;
 	}
 
-	return best - pos;
+	return pos - best;
 }
 
 /* Works only on sorted freq-tables */
-- 
2.10.1.382.ga23ca1b