linux-kernel - [PATCH 4.14 106/166] drivers: char: tlclk.c: Avoid data race between init and interrupt handler

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Date:   Tue, 29 Sep 2020 13:00:18 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 106/166] drivers: char: tlclk.c: Avoid data race between init and interrupt handler

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

[ Upstream commit 44b8fb6eaa7c3fb770bf1e37619cdb3902cca1fc ]

After registering character device the file operation callbacks can be
called. The open callback registers interrupt handler.
Therefore interrupt handler can execute in parallel with rest of the init
function. To avoid such data race initialize telclk_interrupt variable
and struct alarm_events before registering character device.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Link: https://lore.kernel.org/r/20200417153451.1551-1-madhuparnabhowmik10@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/char/tlclk.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/char/tlclk.c b/drivers/char/tlclk.c
index 6210bff46341e..52fadc46e7a97 100644
--- a/drivers/char/tlclk.c
+++ b/drivers/char/tlclk.c
@@ -777,17 +777,21 @@ static int __init tlclk_init(void)
 {
 	int ret;
 
+	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
+
+	alarm_events = kzalloc( sizeof(struct tlclk_alarms), GFP_KERNEL);
+	if (!alarm_events) {
+		ret = -ENOMEM;
+		goto out1;
+	}
+
 	ret = register_chrdev(tlclk_major, "telco_clock", &tlclk_fops);
 	if (ret < 0) {
 		printk(KERN_ERR "tlclk: can't get major %d.\n", tlclk_major);
+		kfree(alarm_events);
 		return ret;
 	}
 	tlclk_major = ret;
-	alarm_events = kzalloc( sizeof(struct tlclk_alarms), GFP_KERNEL);
-	if (!alarm_events) {
-		ret = -ENOMEM;
-		goto out1;
-	}
 
 	/* Read telecom clock IRQ number (Set by BIOS) */
 	if (!request_region(TLCLK_BASE, 8, "telco_clock")) {
@@ -796,7 +800,6 @@ static int __init tlclk_init(void)
 		ret = -EBUSY;
 		goto out2;
 	}
-	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
 
 	if (0x0F == telclk_interrupt ) { /* not MCPBL0010 ? */
 		printk(KERN_ERR "telclk_interrupt = 0x%x non-mcpbl0010 hw.\n",
@@ -837,8 +840,8 @@ out3:
 	release_region(TLCLK_BASE, 8);
 out2:
 	kfree(alarm_events);
-out1:
 	unregister_chrdev(tlclk_major, "telco_clock");
+out1:
 	return ret;
 }
 
-- 
2.25.1