Re: [RFC PATCH v9 05/16] ipe: add userspace interface

[Paul Moore]

On Mon, Jan 30, 2023 at 5:58 PM Fan Wu <wufan@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx>
>
> As is typical with LSMs, IPE uses securityfs as its interface with
> userspace. for a complete list of the interfaces and the respective
> inputs/outputs, please see the documentation under
> admin-guide/LSM/ipe.rst
>
> Signed-off-by: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Fan Wu <wufan@xxxxxxxxxxxxxxxxxxx>

...

> ---
>  security/ipe/Makefile    |   2 +
>  security/ipe/fs.c        | 101 +++++++++
>  security/ipe/fs.h        |  17 ++
>  security/ipe/ipe.c       |   3 +
>  security/ipe/ipe.h       |   2 +
>  security/ipe/policy.c    | 135 ++++++++++++
>  security/ipe/policy.h    |   7 +
>  security/ipe/policy_fs.c | 459 +++++++++++++++++++++++++++++++++++++++
>  8 files changed, 726 insertions(+)
>  create mode 100644 security/ipe/fs.c
>  create mode 100644 security/ipe/fs.h
>  create mode 100644 security/ipe/policy_fs.c

...

> diff --git a/security/ipe/policy.c b/security/ipe/policy.c
> index 772d876b1087..a5e9c6e5691b 100644
> --- a/security/ipe/policy.c
> +++ b/security/ipe/policy.c
> @@ -4,12 +4,39 @@
>   */
>
>  #include "ipe.h"
> +#include "eval.h"
> +#include "fs.h"
>  #include "policy.h"
>  #include "policy_parser.h"
>  #include "digest.h"
>
>  #include <linux/verification.h>
>
> +/* lock for synchronizing writers across ipe policy */
> +DEFINE_SPINLOCK(ipe_policy_lock);
> +
> +/**
> + * ver_to_u64 - Convert an internal ipe_policy_version to a u64.
> + * @p: Policy to extract the version from.
> + *
> + * Bits (LSB is index 0):
> + *     [48,32] -> Major
> + *     [32,16] -> Minor
> + *     [16, 0] -> Revision
> + *
> + * Return: u64 version of the embedded version structure.
> + */
> +static inline u64 ver_to_u64(const struct ipe_policy *const p)
> +{
> +       u64 r = 0;

No need to set @r to 0 since you set it to the version immediately below.

> +       r = (((u64)p->parsed->version.major) << 32)
> +         | (((u64)p->parsed->version.minor) << 16)
> +         | ((u64)(p->parsed->version.rev));
> +
> +       return r;
> +}
> +
>  /**
>   * ipe_free_policy - Deallocate a given IPE policy.
>   * @p: Supplies the policy to free.
> @@ -21,6 +48,7 @@ void ipe_free_policy(struct ipe_policy *p)
>         if (IS_ERR_OR_NULL(p))
>                 return;
>
> +       ipe_del_policyfs_node(p);
>         free_parsed_policy(p->parsed);
>         if (!p->pkcs7)
>                 kfree(p->text);
> @@ -39,6 +67,70 @@ static int set_pkcs7_data(void *ctx, const void *data, size_t len,
>         return 0;
>  }
>
> +/**
> + * ipe_update_policy - parse a new policy and replace @old with it.
> + * @addr: Supplies a pointer to the i_private for saving policy.
> + * @text: Supplies a pointer to the plain text policy.
> + * @textlen: Supplies the length of @text.
> + * @pkcs7: Supplies a pointer to a buffer containing a pkcs7 message.
> + * @pkcs7len: Supplies the length of @pkcs7len.
> + *
> + * @text/@textlen is mutually exclusive with @pkcs7/@pkcs7len - see
> + * ipe_new_policy.
> + *
> + * Return:
> + * * !IS_ERR   - OK
> + * * -ENOENT   - Policy doesn't exist
> + * * -EINVAL   - New policy is invalid
> + */
> +struct ipe_policy *ipe_update_policy(struct ipe_policy __rcu **addr,
> +                                    const char *text, size_t textlen,
> +                                    const char *pkcs7, size_t pkcs7len)
> +{
> +       int rc = 0;
> +       struct ipe_policy *old, *new;
> +
> +       old = ipe_get_policy_rcu(*addr);
> +       if (!old) {
> +               rc = -ENOENT;
> +               goto err;
> +       }
> +
> +       new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
> +       if (IS_ERR(new)) {
> +               rc = PTR_ERR(new);
> +               goto err;
> +       }
> +
> +       if (strcmp(new->parsed->name, old->parsed->name)) {
> +               rc = -EINVAL;
> +               goto err;
> +       }
> +
> +       if (ver_to_u64(old) > ver_to_u64(new)) {
> +               rc = -EINVAL;
> +               goto err;
> +       }
> +
> +       if (ipe_is_policy_active(old)) {

I don't understand the is-active check, you want to make @new the new
active policy regardless, right?  Could this is-active check ever be
false?

> +               spin_lock(&ipe_policy_lock);
> +               rcu_assign_pointer(ipe_active_policy, new);
> +               spin_unlock(&ipe_policy_lock);
> +               synchronize_rcu();
> +       }
> +
> +       rcu_assign_pointer(*addr, new);
> +
> +       swap(new->policyfs, old->policyfs);
> +       ipe_free_policy(old);
> +
> +       goto out;
> +err:
> +       ipe_free_policy(new);
> +out:
> +       return (rc < 0) ? ERR_PTR(rc) : new;
> +}
> +
>  /**
>   * ipe_new_policy - Allocate and parse an ipe_policy structure.
>   *
> @@ -117,3 +209,46 @@ struct ipe_policy *ipe_get_policy_rcu(struct ipe_policy __rcu *p)
>
>         return rv;
>  }
> +
> +/**
> + * ipe_set_active_pol - Make @p the active policy.
> + * @p: Supplies a pointer to the policy to make active.
> + */
> +int ipe_set_active_pol(const struct ipe_policy *p)
> +{
> +       int rc = 0;
> +       struct ipe_policy *ap = NULL;
> +
> +       ap = ipe_get_policy_rcu(ipe_active_policy);
> +       if (ap && ver_to_u64(ap) > ver_to_u64(p)) {
> +               rc = -EINVAL;
> +               goto out;
> +       }
> +
> +       spin_lock(&ipe_policy_lock);
> +       rcu_assign_pointer(ipe_active_policy, p);
> +       spin_unlock(&ipe_policy_lock);
> +       synchronize_rcu();
> +
> +out:
> +       return rc;
> +}
> +
> +/**
> + * ipe_is_policy_active - Determine wehther @p is the active policy.
> + * @p: Supplies a pointer to the policy to check.
> + *
> + * Return:
> + * * true      - @p is the active policy
> + * * false     - @p is not the active policy
> + */
> +bool ipe_is_policy_active(const struct ipe_policy *p)
> +{
> +       bool rv;
> +
> +       rcu_read_lock();
> +       rv = rcu_access_pointer(ipe_active_policy) == p;
> +       rcu_read_unlock();
> +
> +       return rv;
> +}

--
paul-moore.com