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SubjectRe: [PATCH 1/1] cgroups: implement device whitelist (v6)
Quoting Andrew Morton (akpm@linux-foundation.org):
> On Wed, 26 Mar 2008 13:05:43 -0500 "Serge E. Hallyn" <serue@us.ibm.com> wrote:
>
> > (This is identical to the version I sent on Mar 19 in response to
> > the comments by Daniel Hokka Zakrisson, which are the last
> > comments I've gotten.)
> >
> > Implement a cgroup to track and enforce open and mknod restrictions on device
> > files. A device cgroup associates a device access whitelist with each
> > cgroup. A whitelist entry has 4 fields. 'type' is a (all), c (char), or
> > b (block). 'all' means it applies to all types and all major and minor
> > numbers. Major and minor are either an integer or * for all.
> > Access is a composition of r (read), w (write), and m (mknod).
> >
> > The root device cgroup starts with rwm to 'all'. A child devcg gets
> > a copy of the parent. Admins can then remove devices from the
> > whitelist or add new entries. A child cgroup can never receive a
> > device access which is denied its parent. However when a device
> > access is removed from a parent it will not also be removed from the
> > child(ren).
> >
> > An entry is added using devices.allow, and removed using
> > devices.deny. For instance
> >
> > echo 'c 1:3 mr' > /cgroups/1/devices.allow
> >
> > allows cgroup 1 to read and mknod the device usually known as
> > /dev/null. Doing
> >
> > echo a > /cgroups/1/devices.deny
> >
> > will remove the default 'a *:* mrw' entry.
> >
> > CAP_SYS_ADMIN is needed to change permissions or move another task
> > to a new cgroup. A cgroup may not be granted more permissions than
> > the cgroup's parent has. Any task can move itself between cgroups.
> > This won't be sufficient, but we can decide the best way to
> > adequately restrict movement later.
>
> The above should be in Documentation/cgroups.txt?
>
> > +static char *print_whitelist(struct dev_cgroup *devcgroup, int *len)
> > +{
> > + char *buf, *s, acc[4];
> > + struct dev_whitelist_item *wh;
> > + int ret;
> > + int count = 0;
> > + char maj[10], min[10];
> > +
> > + buf = kmalloc(4096, GFP_KERNEL);
> > + if (!buf)
> > + return ERR_PTR(-ENOMEM);
> > + s = buf;
> > + *s = '\0';
> > + *len = 0;
> > +
> > + spin_lock(&devcgroup->lock);
> > + list_for_each_entry(wh, &devcgroup->whitelist, list) {
> > + set_access(acc, wh->access);
> > + set_majmin(maj, 10, wh->major);
> > + set_majmin(min, 10, wh->minor);
> > + ret = snprintf(s, 4095-(s-buf), "%c %s:%s %s\n",
> > + type_to_char(wh->type), maj, min, acc);
> > + if (s+ret >= buf+4095) {
> > + kfree(buf);
> > + buf = ERR_PTR(-ENOMEM);
> > + break;
> > + }
> > + s += ret;
> > + *len += ret;
> > + count++;
> > + }
> > + spin_unlock(&devcgroup->lock);
> > +
> > + return buf;
> > +}
>
> That's rather ugly-looking. We can't use seq_file here?

I can do that, but then it will probably be cleaner if I split the
file into one for read and one for write.

Paul, did you have any plans of offering some sort of cft->read_seq()
helper? Having both the cft-> helpers and the subsystem code play
with ->private fields and caching the cgroup isn't very palletable.

thanks,
-serge


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