Re: [PATCH] nvmem: core: make default user binary file root-access only

[Srinivas Kandagatla]

On 07/10/15 18:12, Greg KH wrote:
> On Wed, Oct 07, 2015 at 06:01:03PM +0100, Srinivas Kandagatla wrote:
> > On 07/10/15 17:50, Greg KH wrote:
> > > On Wed, Oct 07, 2015 at 05:35:14PM +0100, Srinivas Kandagatla wrote:
> > > > As required by many providers like at24/at25/mxs-ocotp/qfprom, which would
> > > > want to allow root-only to read/write the nvmem content.
> > > > So making the defaults to be root-only access which can prevent normal
> > > > users from reading the nvmem data.
> > > >
> > > > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > > > ---
> > > >   drivers/nvmem/core.c | 4 ++--
> > > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > > > index 6fd4e5a..4d2e476 100644
> > > > --- a/drivers/nvmem/core.c
> > > > +++ b/drivers/nvmem/core.c
> > > > @@ -112,7 +112,7 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
> > > >   static struct bin_attribute bin_attr_rw_nvmem = {
> > > >   	.attr	= {
> > > >   		.name	= "nvmem",
> > > > -		.mode	= S_IWUSR | S_IRUGO,
> > > > +		.mode	= S_IWUSR | S_IRUSR,
> > > >   	},
> > > >   	.read	= bin_attr_nvmem_read,
> > > >   	.write	= bin_attr_nvmem_write,
> > > > @@ -136,7 +136,7 @@ static const struct attribute_group *nvmem_rw_dev_groups[] = {
> > > >   static struct bin_attribute bin_attr_ro_nvmem = {
> > > >   	.attr	= {
> > > >   		.name	= "nvmem",
> > > > -		.mode	= S_IRUGO,
> > > > +		.mode	= S_IRUSR,
> > > >   	},
> > > >   	.read	= bin_attr_nvmem_read,
> > > >   };
> > >
> > > How about using BIN_ATTR_RO() and friends instead, that way I _know_ you
> > > got the permissions correct as it's impossible to get them wrong by
> > > using those macros.
> > Yes, that sounds good, but there are no macros for just "S_IRUSR" or
> > "(S_IWUSR | S_IRUSR)" in ./include/linux/sysfs.h
>
> Then that means you are trying to do something "odd" and you shouldn't
> be doing that :)
The requirement originally came from a discussion regarding file 
permissions set by at24 (drivers/mis/eeprom/at24.c) vs nvmem.

at24 driver sets the permission of root-only read/write, which is 
different to what nvmem sets as default.

So this patch was primarily make nvmem framework inline with what 
at24/at25 does.

Other argument was regarding the content of the nvmem which could have 
things like keys and normal user should not be allowed read it.

--srini
> Use the standard attribute permissions (RO, RW), as those are the
> "safest" and what you really want to be using here, as you already are.

> thanks,
>
> greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/