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

From: Greg KH
Date: Wed Oct 07 2015 - 13:12:34 EST


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 :)

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
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