[PATCH] driver core: restrict buffer length in online_store()

[Tiezhu Yang]

According to Documentation/ABI/testing/sysfs-devices-online, in order to
control CPU N's hotplug state, we should write one of 'Yy1Nn0' to the file
/sys/devices/system/cpu/cpuN/online, other values should be invalid. so the
buffer length should be 2, buf[0] is one of 'Yy1Nn0' and buf[1] is '\n'.

without patch:
[root@localhost home]# echo 0test > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
0
[root@localhost home]# echo 1test > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
1
[root@localhost home]# echo ntest > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
0
[root@localhost home]# echo ytest > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
1
[root@localhost home]# echo Ntest > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
0
[root@localhost home]# echo Ytest > /sys/devices/system/cpu/cpu1/online
[root@localhost home]# cat /sys/devices/system/cpu/cpu1/online
1

with patch:
[root@localhost home]# echo 0test > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument
[root@localhost home]# echo 1test > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument
[root@localhost home]# echo ntest > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument
[root@localhost home]# echo ytest > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument
[root@localhost home]# echo Ntest > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument
[root@localhost home]# echo Ytest > /sys/devices/system/cpu/cpu1/online
bash: echo: write error: Invalid argument

Signed-off-by: Tiezhu Yang <kernelpatch@xxxxxxx>
---
 drivers/base/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 755451f..6588ed5 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1005,6 +1005,12 @@ static ssize_t online_store(struct device *dev, struct device_attribute *attr,
 	bool val;
 	int ret;
 
+	/* According to Documentation/ABI/testing/sysfs-devices-online,
+	 * the buf length should be 2, buf[0]: one of 'Yy1Nn0', buf[1]: '\n'.
+	 */
+	if (strlen(buf) != 2)
+		return -EINVAL;
+
 	ret = strtobool(buf, &val);
 	if (ret < 0)
 		return ret;
-- 
1.8.3.1