Re: [PATCH v2 2/3] sysfs: Only accept read/write permissions for file attributes

[Guenter Roeck]

On 03/12/2015 03:01 AM, Greg Kroah-Hartman wrote:
> On Wed, Mar 11, 2015 at 02:22:10PM -0400, Vivien Didelot wrote:
> > For sysfs file attributes, only read and write permissions make sense.
> > Mask provided attribute permissions accordingly and send a warning
> > to the console if invalid permission bits are set.
> >
> > This patch is originally from Guenter [1] and includes the fixup
> > explained in the thread, that is printing permissions in octal format
> > and limiting the scope of attributes to SYSFS_PREALLOC | 0664.
> >
> > [1] https://lkml.org/lkml/2015/1/19/599
> >
> > Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Signed-off-by: Vivien Didelot <vivien.didelot@xxxxxxxxxxxxxxxxxxxx>
> > ---
> >   fs/sysfs/group.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> > index 3fdccd9..b400c04 100644
> > --- a/fs/sysfs/group.c
> > +++ b/fs/sysfs/group.c
> > @@ -55,6 +55,12 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
> >   				if (!mode)
> >   					continue;
> >   			}
> > +
> > +			WARN(mode & ~(SYSFS_PREALLOC | 0664),
> > +			     "Attribute %s: Invalid permissions 0%o\n",
> > +			     (*attr)->name, mode);
> > +
> > +			mode &= SYSFS_PREALLOC | 0664;
>
> How does a "normal" boot look with this warning in place?  There still
> seem to be a number of files in sysfs that might trigger this.
I was under the impression that they all were addressed, but I may have
missed some pattern(s). Can you point me to an example, by any chance ?

> Also, we have a build-time warning if a sysfs file is this type of
> attribute, shouldn't we just rely on that instead of this run-time
> warning?

The mode value can be returned from an is_visible function, and even if not
there is no guarantee that the build-time warning triggers (attribute lists
can be generated manually, for example).

Thanks,
Guenter

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