Re: [PATCH 1/5] libnvdimm: fix updating of kernel key during nvdimm key update

[Dan Williams <dan.j.williams@intel.com>]

On Fri, Oct 12, 2018 at 11:23 AM Dave Jiang <dave.jiang@intel.com> wrote:
>
> There are several issues WRT kernel key update when we are doing nvdimm
> security key update.
>
> 1. The kernel key created needs to have proper permission for update
> 2. We need to check key_update() return value and make sure it didn't fail
> 3. We need to not hold the key->sem when calling key_update() since it will
>    call down_write() when doing modification to the key.
>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/nvdimm/security.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvdimm/security.c b/drivers/nvdimm/security.c
> index 776c440a02ef..ef83bdf47c31 100644
> --- a/drivers/nvdimm/security.c
> +++ b/drivers/nvdimm/security.c
> @@ -27,7 +27,7 @@ static struct key *make_kernel_key(struct key *key)
>
>         new_key = key_alloc(&key_type_logon, key->description,
>                         GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
> -                       KEY_POS_SEARCH, KEY_ALLOC_NOT_IN_QUOTA, NULL);
> +                       KEY_POS_ALL, KEY_ALLOC_NOT_IN_QUOTA, NULL);

Should that be (KEY_POS_ALL & ~KEY_POS_SETATTR)? I don't see a reason
why we would ever change key attributes.

>         if (IS_ERR(new_key))
>                 return NULL;
>
> @@ -419,11 +419,19 @@ int nvdimm_security_change_key(struct nvdimm *nvdimm,
>                 dev_warn(dev, "key update failed: %d\n", rc);
>
>         if (old_key) {
> +               up_read(&old_key->sem);
>                 /* copy new payload to old payload */

Let's delete that comment and replace it with one that talks about the
locking rules. Namely that we are done with the old_key payload after
->change_key() returns and that key_update() will take the write lock
on the payload to update it.

> -               if (rc == 0)
> -                       key_update(make_key_ref(old_key, 1), new_data,
> +               if (rc == 0) {
> +                       rc = key_update(make_key_ref(old_key, 1), new_data,
>                                         old_key->datalen);
> -               up_read(&old_key->sem);
> +                       if (rc < 0) {
> +                               dev_warn(dev,
> +                                       "kernel key update failed: %d\n", rc);
> +                               key_invalidate(old_key);
> +                               key_put(old_key);

I added a local 'key_destroy()' helper for that invalidate+put pattern.
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