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Subject[PATCH] driver core: restrict buffer length in online_store()
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@126.com>
---
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
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