linux-kernel - Re: [PATCH 11/23] fs: Add /proc/namespaces/ directory

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Date:   Thu, 30 Jul 2020 16:22:21 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     viro@...iv.linux.org.uk, davem@...emloft.net,
        ebiederm@...ssion.com, akpm@...ux-foundation.org,
        christian.brauner@...ntu.com, areber@...hat.com, serge@...lyn.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 11/23] fs: Add /proc/namespaces/ directory

On 30.07.2020 15:18, Alexey Dobriyan wrote:
> On Thu, Jul 30, 2020 at 03:00:19PM +0300, Kirill Tkhai wrote:
> 
>> # ls /proc/namespaces/ -l
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'cgroup:[4026531835]' -> 'cgroup:[4026531835]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'ipc:[4026531839]' -> 'ipc:[4026531839]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531840]' -> 'mnt:[4026531840]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026531861]' -> 'mnt:[4026531861]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532133]' -> 'mnt:[4026532133]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532134]' -> 'mnt:[4026532134]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532135]' -> 'mnt:[4026532135]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'mnt:[4026532136]' -> 'mnt:[4026532136]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'net:[4026531993]' -> 'net:[4026531993]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'pid:[4026531836]' -> 'pid:[4026531836]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'time:[4026531834]' -> 'time:[4026531834]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'user:[4026531837]' -> 'user:[4026531837]'
>> lrwxrwxrwx 1 root root 0 Jul 29 16:50 'uts:[4026531838]' -> 'uts:[4026531838]'
> 
> I'd say make it '%s-%llu'. The brackets don't carry any information.
> And ':' forces quoting with recent coreutils.
> 
>> +static int parse_namespace_dentry_name(const struct dentry *dentry,
>> +		const char **type, unsigned int *type_len, unsigned int *inum)
>> +{
>> +	const char *p, *name;
>> +	int count;
>> +
>> +	*type = name = dentry->d_name.name;
>> +	p = strchr(name, ':');
>> +	*type_len = p - name;
>> +	if (!p || p == name)
>> +		return -ENOENT;
>> +
>> +	p += 1;
>> +	if (sscanf(p, "[%u]%n", inum, &count) != 1 || *(p + count) != '\0' ||
>> +	    *inum < PROC_NS_MIN_INO)
>> +		return -ENOENT;
> 
> sscanf is banned from lookup code due to lax whitespace rules.
> See
> 
> 	commit ac7f1061c2c11bb8936b1b6a94cdb48de732f7a4
> 	proc: fix /proc/*/map_files lookup

Ok, thanks for pointing this.

> Of course someone sneaked in 1 instance, yikes.
> 
> 	$ grep -e scanf -n -r fs/proc/
> 	fs/proc/base.c:1596:            err = sscanf(pos, "%9s %lld %lu", clock,
> 
>> +static int proc_namespaces_readdir(struct file *file, struct dir_context *ctx)
> 
>> +		len = snprintf(name, sizeof(name), "%s:[%u]", ns->ops->name, inum);
> 
> [] -- no need.
>