Re: [PATCH v10 3/3] btrfs: create read policy sysfs attribute, pid

[Anand Jain <anand.jain@oracle.com>]

On 30/10/20 12:45 am, David Sterba wrote:
> On Wed, Oct 28, 2020 at 09:14:47PM +0800, Anand Jain wrote:
>> +static ssize_t btrfs_read_policy_store(struct kobject *kobj,
>> +				       struct kobj_attribute *a,
>> +				       const char *buf, size_t len)
>> +{
>> +	int i;
>> +	struct btrfs_fs_devices *fs_devices = to_fs_devs(kobj);
>> +
>> +	for (i = 0; i < BTRFS_NR_READ_POLICY; i++) {
>> +		if (btrfs_strmatch(buf, btrfs_read_policy_name[i])) {
> 
> Does sysfs guarantee that the buf is nul terminated string or that it
> contains a null at all? Because if not, the skip_space step of strmatch
> could run out of the buffer.
> 

It does

[  173.555507]  ? btrfs_read_policy_store+0x3e/0x12d [btrfs]
[  173.555541]  ? kobj_attr_store+0x16/0x30
[  173.555562]  ? sysfs_kf_write+0x54/0x80
[  173.555582]  ? kernfs_fop_write+0xfa/0x290
[  173.555611]  ? vfs_write+0xee/0x2f0
[  173.555641]  ? ksys_write+0x80/0x170
[  173.555671]  ? __x64_sys_write+0x1e/0x30
[  173.555692]  ? do_syscall_64+0x4b/0x80
[  173.555708]  ? entry_SYSCALL_64_after_hwframe+0x44/0xa9


static ssize_t kernfs_fop_write(struct file *file, const char __user 
*user_buf,
                                 size_t count, loff_t *ppos)
{
::
         buf[len] = '\0';        /* guarantee string termination */


Thanks, Anand