drivers: char: tlclk.c: Avoid data race between init and interrupt handler

[ 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@gmail.com>
Link: https://lore.kernel.org/r/20200417153451.1551-1-madhuparnabhowmik10@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/char/tlclk.c b/drivers/char/tlclk.c
index 6210bff46341e88b2eb2b19028f41004849cf2bc..52fadc46e7a97a9b07d35c4b403415f48f2e8ce3 100644 (file)
--- 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;
 }