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Date:   Thu, 29 Oct 2020 20:30:18 +0100
From:   David Sterba <dsterba@suse.cz>
To:     Anand Jain <anand.jain@oracle.com>
Cc:     dsterba@suse.cz, linux-btrfs@vger.kernel.org,
        Josef Bacik <josef@toxicpanda.com>
Subject: Re: [PATCH v10 3/3] btrfs: create read policy sysfs attribute, pid
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On Fri, Oct 30, 2020 at 03:30:10AM +0800, Anand Jain wrote:
> 
> 
> 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 */

Ok thanks.