diff mbox series

[RFC,v12,08/20] ipe: add userspace interface

Message ID 1706654228-17180-9-git-send-email-wufan@linux.microsoft.com (mailing list archive)
State Handled Elsewhere
Delegated to: Paul Moore
Headers show
Series Integrity Policy Enforcement LSM (IPE) | expand

Commit Message

Fan Wu Jan. 30, 2024, 10:36 p.m. UTC
From: Deven Bowers <deven.desai@linux.microsoft.com>

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@linux.microsoft.com>
Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

---
v2:
  + Split evaluation loop, access control hooks,
    and evaluation loop from policy parser and userspace
    interface to pass mailing list character limit

v3:
  + Move policy load and activation audit event to 03/12
  + Fix a potential panic when a policy failed to load.
  + use pr_warn for a failure to parse instead of an
    audit record
  + Remove comments from headers
  + Add lockdep assertions to ipe_update_active_policy and
    ipe_activate_policy
  + Fix up warnings with checkpatch --strict
  + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
    nodes.
  + Use memdup_user instead of kzalloc+simple_write_to_buffer.
  + Remove strict_parse command line parameter, as it is added
    by the sysctl command line.
  + Prefix extern variables with ipe_

v4:
  + Remove securityfs to reverse-dependency
  + Add SHA1 reverse dependency.
  + Add versioning scheme for IPE properties, and associated
    interface to query the versioning scheme.
  + Cause a parser to always return an error on unknown syntax.
  + Remove strict_parse option
  + Change active_policy interface from sysctl, to securityfs,
    and change scheme.

v5:
  + Cause an error if a default action is not defined for each
    operation.
  + Minor function renames

v6:
  + No changes

v7:
  + Propagating changes to support the new ipe_context structure in the
    evaluation loop.

  + Further split the parser and userspace interface changes into
    separate commits.

  + "raw" was renamed to "pkcs7" and made read only
  + "raw"'s write functionality (update a policy) moved to "update"
  + introduced "version", "policy_name" nodes.
  + "content" renamed to "policy"
  + changes to allow the compiled-in policy to be treated
    identical to deployed-after-the-fact policies.

v8:
  + Prevent securityfs initialization if the LSM is disabled

v9:
  + Switch to securityfs_recursive_remove for policy folder deletion

v10:
  + Simplify and correct concurrency
  + Fix typos

v11:
  + Correct code comments

v12:
  + Correct locking and remove redundant code
---
 security/ipe/Makefile    |   2 +
 security/ipe/fs.c        | 101 +++++++++
 security/ipe/fs.h        |  16 ++
 security/ipe/ipe.c       |   3 +
 security/ipe/ipe.h       |   2 +
 security/ipe/policy.c    | 123 ++++++++++
 security/ipe/policy.h    |   9 +
 security/ipe/policy_fs.c | 469 +++++++++++++++++++++++++++++++++++++++
 8 files changed, 725 insertions(+)
 create mode 100644 security/ipe/fs.c
 create mode 100644 security/ipe/fs.h
 create mode 100644 security/ipe/policy_fs.c

Comments

Paul Moore Feb. 3, 2024, 10:25 p.m. UTC | #1
On Jan 30, 2024 Fan Wu <wufan@linux.microsoft.com> wrote:
> 
> 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@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
> ---
> v2:
>   + Split evaluation loop, access control hooks,
>     and evaluation loop from policy parser and userspace
>     interface to pass mailing list character limit
> 
> v3:
>   + Move policy load and activation audit event to 03/12
>   + Fix a potential panic when a policy failed to load.
>   + use pr_warn for a failure to parse instead of an
>     audit record
>   + Remove comments from headers
>   + Add lockdep assertions to ipe_update_active_policy and
>     ipe_activate_policy
>   + Fix up warnings with checkpatch --strict
>   + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
>     nodes.
>   + Use memdup_user instead of kzalloc+simple_write_to_buffer.
>   + Remove strict_parse command line parameter, as it is added
>     by the sysctl command line.
>   + Prefix extern variables with ipe_
> 
> v4:
>   + Remove securityfs to reverse-dependency
>   + Add SHA1 reverse dependency.
>   + Add versioning scheme for IPE properties, and associated
>     interface to query the versioning scheme.
>   + Cause a parser to always return an error on unknown syntax.
>   + Remove strict_parse option
>   + Change active_policy interface from sysctl, to securityfs,
>     and change scheme.
> 
> v5:
>   + Cause an error if a default action is not defined for each
>     operation.
>   + Minor function renames
> 
> v6:
>   + No changes
> 
> v7:
>   + Propagating changes to support the new ipe_context structure in the
>     evaluation loop.
> 
>   + Further split the parser and userspace interface changes into
>     separate commits.
> 
>   + "raw" was renamed to "pkcs7" and made read only
>   + "raw"'s write functionality (update a policy) moved to "update"
>   + introduced "version", "policy_name" nodes.
>   + "content" renamed to "policy"
>   + changes to allow the compiled-in policy to be treated
>     identical to deployed-after-the-fact policies.
> 
> v8:
>   + Prevent securityfs initialization if the LSM is disabled
> 
> v9:
>   + Switch to securityfs_recursive_remove for policy folder deletion
> 
> v10:
>   + Simplify and correct concurrency
>   + Fix typos
> 
> v11:
>   + Correct code comments
> 
> v12:
>   + Correct locking and remove redundant code
> ---
>  security/ipe/Makefile    |   2 +
>  security/ipe/fs.c        | 101 +++++++++
>  security/ipe/fs.h        |  16 ++
>  security/ipe/ipe.c       |   3 +
>  security/ipe/ipe.h       |   2 +
>  security/ipe/policy.c    | 123 ++++++++++
>  security/ipe/policy.h    |   9 +
>  security/ipe/policy_fs.c | 469 +++++++++++++++++++++++++++++++++++++++
>  8 files changed, 725 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 f22a576a6d68..61fea3e38e11 100644
> --- a/security/ipe/policy.c
> +++ b/security/ipe/policy.c
> @@ -43,6 +71,68 @@ 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.
> + * @root: Supplies a pointer to the securityfs inode saved the 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.
> + *
> + * Context: Requires root->i_rwsem to be held.
> + * Return:
> + * * !IS_ERR	- The existing policy saved in the inode before update
> + * * -ENOENT	- Policy doesn't exist
> + * * -EINVAL	- New policy is invalid
> + */
> +struct ipe_policy *ipe_update_policy(struct inode *root,
> +				     const char *text, size_t textlen,
> +				     const char *pkcs7, size_t pkcs7len)
> +{
> +	int rc = 0;
> +	struct ipe_policy *old, *ap, *new = NULL;
> +
> +	old = (struct ipe_policy *)root->i_private;
> +	if (!old)
> +		return ERR_PTR(-ENOENT);
> +
> +	new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
> +	if (IS_ERR(new))
> +		return new;
> +
> +	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;
> +	}
> +
> +	root->i_private = new;
> +	swap(new->policyfs, old->policyfs);

Should the swap() take place with @ipe_policy_lock held?

> +	mutex_lock(&ipe_policy_lock);
> +	ap = rcu_dereference_protected(ipe_active_policy,
> +				       lockdep_is_held(&ipe_policy_lock));
> +	if (old == ap) {
> +		rcu_assign_pointer(ipe_active_policy, new);
> +		mutex_unlock(&ipe_policy_lock);
> +		synchronize_rcu();

I'm guessing you are forcing a synchronize_rcu() here because you are
free()'ing @old in the caller, yes?  Looking at the code, I only see
one caller, update_policy().  With only one caller, why not free @old
directly in ipe_update_policy()?  Do you see others callers that would
do something different?

> +	} else {
> +		mutex_unlock(&ipe_policy_lock);
> +	}
> +
> +	return old;
> +err:
> +	ipe_free_policy(new);
> +	return ERR_PTR(rc);
> +}
> +
>  /**
>   * ipe_new_policy - Allocate and parse an ipe_policy structure.
>   *
> @@ -99,3 +189,36 @@ struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
>  	ipe_free_policy(new);
>  	return ERR_PTR(rc);
>  }
> +
> +/**
> + * ipe_set_active_pol - Make @p the active policy.
> + * @p: Supplies a pointer to the policy to make active.
> + *
> + * Context: Requires root->i_rwsem, which i_private has the policy, to be held.
> + * Return:
> + * * !IS_ERR	- Success
> + * * -EINVAL	- New active policy version is invalid
> + */
> +int ipe_set_active_pol(const struct ipe_policy *p)
> +{
> +	struct ipe_policy *ap = NULL;
> +
> +	mutex_lock(&ipe_policy_lock);
> +
> +	ap = rcu_dereference_protected(ipe_active_policy,
> +				       lockdep_is_held(&ipe_policy_lock));
> +	if (ap == p) {
> +		mutex_unlock(&ipe_policy_lock);
> +		return 0;
> +	}
> +	if (ap && ver_to_u64(ap) > ver_to_u64(p)) {
> +		mutex_unlock(&ipe_policy_lock);
> +		return -EINVAL;
> +	}
> +
> +	rcu_assign_pointer(ipe_active_policy, p);
> +	mutex_unlock(&ipe_policy_lock);
> +	synchronize_rcu();

Why do you need the synchronize_rcu() call here?

> +	return 0;
> +}


--
paul-moore.com
Fan Wu Feb. 5, 2024, 11:01 p.m. UTC | #2
On 2/3/2024 2:25 PM, Paul Moore wrote:
> On Jan 30, 2024 Fan Wu <wufan@linux.microsoft.com> wrote:
>>
>> 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@linux.microsoft.com>
>> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
>> ---
>> v2:
>>    + Split evaluation loop, access control hooks,
>>      and evaluation loop from policy parser and userspace
>>      interface to pass mailing list character limit
>>
>> v3:
>>    + Move policy load and activation audit event to 03/12
>>    + Fix a potential panic when a policy failed to load.
>>    + use pr_warn for a failure to parse instead of an
>>      audit record
>>    + Remove comments from headers
>>    + Add lockdep assertions to ipe_update_active_policy and
>>      ipe_activate_policy
>>    + Fix up warnings with checkpatch --strict
>>    + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
>>      nodes.
>>    + Use memdup_user instead of kzalloc+simple_write_to_buffer.
>>    + Remove strict_parse command line parameter, as it is added
>>      by the sysctl command line.
>>    + Prefix extern variables with ipe_
>>
>> v4:
>>    + Remove securityfs to reverse-dependency
>>    + Add SHA1 reverse dependency.
>>    + Add versioning scheme for IPE properties, and associated
>>      interface to query the versioning scheme.
>>    + Cause a parser to always return an error on unknown syntax.
>>    + Remove strict_parse option
>>    + Change active_policy interface from sysctl, to securityfs,
>>      and change scheme.
>>
>> v5:
>>    + Cause an error if a default action is not defined for each
>>      operation.
>>    + Minor function renames
>>
>> v6:
>>    + No changes
>>
>> v7:
>>    + Propagating changes to support the new ipe_context structure in the
>>      evaluation loop.
>>
>>    + Further split the parser and userspace interface changes into
>>      separate commits.
>>
>>    + "raw" was renamed to "pkcs7" and made read only
>>    + "raw"'s write functionality (update a policy) moved to "update"
>>    + introduced "version", "policy_name" nodes.
>>    + "content" renamed to "policy"
>>    + changes to allow the compiled-in policy to be treated
>>      identical to deployed-after-the-fact policies.
>>
>> v8:
>>    + Prevent securityfs initialization if the LSM is disabled
>>
>> v9:
>>    + Switch to securityfs_recursive_remove for policy folder deletion
>>
>> v10:
>>    + Simplify and correct concurrency
>>    + Fix typos
>>
>> v11:
>>    + Correct code comments
>>
>> v12:
>>    + Correct locking and remove redundant code
>> ---
>>   security/ipe/Makefile    |   2 +
>>   security/ipe/fs.c        | 101 +++++++++
>>   security/ipe/fs.h        |  16 ++
>>   security/ipe/ipe.c       |   3 +
>>   security/ipe/ipe.h       |   2 +
>>   security/ipe/policy.c    | 123 ++++++++++
>>   security/ipe/policy.h    |   9 +
>>   security/ipe/policy_fs.c | 469 +++++++++++++++++++++++++++++++++++++++
>>   8 files changed, 725 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 f22a576a6d68..61fea3e38e11 100644
>> --- a/security/ipe/policy.c
>> +++ b/security/ipe/policy.c
>> @@ -43,6 +71,68 @@ 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.
>> + * @root: Supplies a pointer to the securityfs inode saved the 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.
>> + *
>> + * Context: Requires root->i_rwsem to be held.
>> + * Return:
>> + * * !IS_ERR	- The existing policy saved in the inode before update
>> + * * -ENOENT	- Policy doesn't exist
>> + * * -EINVAL	- New policy is invalid
>> + */
>> +struct ipe_policy *ipe_update_policy(struct inode *root,
>> +				     const char *text, size_t textlen,
>> +				     const char *pkcs7, size_t pkcs7len)
>> +{
>> +	int rc = 0;
>> +	struct ipe_policy *old, *ap, *new = NULL;
>> +
>> +	old = (struct ipe_policy *)root->i_private;
>> +	if (!old)
>> +		return ERR_PTR(-ENOENT);
>> +
>> +	new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
>> +	if (IS_ERR(new))
>> +		return new;
>> +
>> +	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;
>> +	}
>> +
>> +	root->i_private = new;
>> +	swap(new->policyfs, old->policyfs);
> 
> Should the swap() take place with @ipe_policy_lock held?
> 
I think we are safe here because root->i_rwsem is held. Other two 
operations set_active and delete are also depending on the inode lock.
>> +	mutex_lock(&ipe_policy_lock);
>> +	ap = rcu_dereference_protected(ipe_active_policy,
>> +				       lockdep_is_held(&ipe_policy_lock));
>> +	if (old == ap) {
>> +		rcu_assign_pointer(ipe_active_policy, new);
>> +		mutex_unlock(&ipe_policy_lock);
>> +		synchronize_rcu();
> 
> I'm guessing you are forcing a synchronize_rcu() here because you are
> free()'ing @old in the caller, yes?  Looking at the code, I only see
> one caller, update_policy().  With only one caller, why not free @old
> directly in ipe_update_policy()?  Do you see others callers that would
> do something different?
> 
The call of synchronize_rcu() is because we are updating the current 
active policy so we need to set the new policy as active.

I do agree we can free the old inside this function.
>> +	} else {
>> +		mutex_unlock(&ipe_policy_lock);
>> +	}
>> +
>> +	return old;
>> +err:
>> +	ipe_free_policy(new);
>> +	return ERR_PTR(rc);
>> +}
>> +
>>   /**
>>    * ipe_new_policy - Allocate and parse an ipe_policy structure.
>>    *
>> @@ -99,3 +189,36 @@ struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
>>   	ipe_free_policy(new);
>>   	return ERR_PTR(rc);
>>   }
>> +
>> +/**
>> + * ipe_set_active_pol - Make @p the active policy.
>> + * @p: Supplies a pointer to the policy to make active.
>> + *
>> + * Context: Requires root->i_rwsem, which i_private has the policy, to be held.
>> + * Return:
>> + * * !IS_ERR	- Success
>> + * * -EINVAL	- New active policy version is invalid
>> + */
>> +int ipe_set_active_pol(const struct ipe_policy *p)
>> +{
>> +	struct ipe_policy *ap = NULL;
>> +
>> +	mutex_lock(&ipe_policy_lock);
>> +
>> +	ap = rcu_dereference_protected(ipe_active_policy,
>> +				       lockdep_is_held(&ipe_policy_lock));
>> +	if (ap == p) {
>> +		mutex_unlock(&ipe_policy_lock);
>> +		return 0;
>> +	}
>> +	if (ap && ver_to_u64(ap) > ver_to_u64(p)) {
>> +		mutex_unlock(&ipe_policy_lock);
>> +		return -EINVAL;
>> +	}
>> +
>> +	rcu_assign_pointer(ipe_active_policy, p);
>> +	mutex_unlock(&ipe_policy_lock);
>> +	synchronize_rcu();
> 
> Why do you need the synchronize_rcu() call here?
> 
>> +	return 0;
>> +}
> 
> 
> --
> paul-moore.com
Paul Moore Feb. 5, 2024, 11:10 p.m. UTC | #3
On Mon, Feb 5, 2024 at 6:01 PM Fan Wu <wufan@linux.microsoft.com> wrote:
> On 2/3/2024 2:25 PM, Paul Moore wrote:
> > On Jan 30, 2024 Fan Wu <wufan@linux.microsoft.com> wrote:
> >>
> >> 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@linux.microsoft.com>
> >> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
> >> ---
> >> v2:
> >>    + Split evaluation loop, access control hooks,
> >>      and evaluation loop from policy parser and userspace
> >>      interface to pass mailing list character limit
> >>
> >> v3:
> >>    + Move policy load and activation audit event to 03/12
> >>    + Fix a potential panic when a policy failed to load.
> >>    + use pr_warn for a failure to parse instead of an
> >>      audit record
> >>    + Remove comments from headers
> >>    + Add lockdep assertions to ipe_update_active_policy and
> >>      ipe_activate_policy
> >>    + Fix up warnings with checkpatch --strict
> >>    + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
> >>      nodes.
> >>    + Use memdup_user instead of kzalloc+simple_write_to_buffer.
> >>    + Remove strict_parse command line parameter, as it is added
> >>      by the sysctl command line.
> >>    + Prefix extern variables with ipe_
> >>
> >> v4:
> >>    + Remove securityfs to reverse-dependency
> >>    + Add SHA1 reverse dependency.
> >>    + Add versioning scheme for IPE properties, and associated
> >>      interface to query the versioning scheme.
> >>    + Cause a parser to always return an error on unknown syntax.
> >>    + Remove strict_parse option
> >>    + Change active_policy interface from sysctl, to securityfs,
> >>      and change scheme.
> >>
> >> v5:
> >>    + Cause an error if a default action is not defined for each
> >>      operation.
> >>    + Minor function renames
> >>
> >> v6:
> >>    + No changes
> >>
> >> v7:
> >>    + Propagating changes to support the new ipe_context structure in the
> >>      evaluation loop.
> >>
> >>    + Further split the parser and userspace interface changes into
> >>      separate commits.
> >>
> >>    + "raw" was renamed to "pkcs7" and made read only
> >>    + "raw"'s write functionality (update a policy) moved to "update"
> >>    + introduced "version", "policy_name" nodes.
> >>    + "content" renamed to "policy"
> >>    + changes to allow the compiled-in policy to be treated
> >>      identical to deployed-after-the-fact policies.
> >>
> >> v8:
> >>    + Prevent securityfs initialization if the LSM is disabled
> >>
> >> v9:
> >>    + Switch to securityfs_recursive_remove for policy folder deletion
> >>
> >> v10:
> >>    + Simplify and correct concurrency
> >>    + Fix typos
> >>
> >> v11:
> >>    + Correct code comments
> >>
> >> v12:
> >>    + Correct locking and remove redundant code
> >> ---
> >>   security/ipe/Makefile    |   2 +
> >>   security/ipe/fs.c        | 101 +++++++++
> >>   security/ipe/fs.h        |  16 ++
> >>   security/ipe/ipe.c       |   3 +
> >>   security/ipe/ipe.h       |   2 +
> >>   security/ipe/policy.c    | 123 ++++++++++
> >>   security/ipe/policy.h    |   9 +
> >>   security/ipe/policy_fs.c | 469 +++++++++++++++++++++++++++++++++++++++
> >>   8 files changed, 725 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 f22a576a6d68..61fea3e38e11 100644
> >> --- a/security/ipe/policy.c
> >> +++ b/security/ipe/policy.c
> >> @@ -43,6 +71,68 @@ 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.
> >> + * @root: Supplies a pointer to the securityfs inode saved the 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.
> >> + *
> >> + * Context: Requires root->i_rwsem to be held.
> >> + * Return:
> >> + * * !IS_ERR        - The existing policy saved in the inode before update
> >> + * * -ENOENT        - Policy doesn't exist
> >> + * * -EINVAL        - New policy is invalid
> >> + */
> >> +struct ipe_policy *ipe_update_policy(struct inode *root,
> >> +                                 const char *text, size_t textlen,
> >> +                                 const char *pkcs7, size_t pkcs7len)
> >> +{
> >> +    int rc = 0;
> >> +    struct ipe_policy *old, *ap, *new = NULL;
> >> +
> >> +    old = (struct ipe_policy *)root->i_private;
> >> +    if (!old)
> >> +            return ERR_PTR(-ENOENT);
> >> +
> >> +    new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
> >> +    if (IS_ERR(new))
> >> +            return new;
> >> +
> >> +    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;
> >> +    }
> >> +
> >> +    root->i_private = new;
> >> +    swap(new->policyfs, old->policyfs);
> >
> > Should the swap() take place with @ipe_policy_lock held?
> >
> I think we are safe here because root->i_rwsem is held. Other two
> operations set_active and delete are also depending on the inode lock.
> >> +    mutex_lock(&ipe_policy_lock);
> >> +    ap = rcu_dereference_protected(ipe_active_policy,
> >> +                                   lockdep_is_held(&ipe_policy_lock));
> >> +    if (old == ap) {
> >> +            rcu_assign_pointer(ipe_active_policy, new);
> >> +            mutex_unlock(&ipe_policy_lock);
> >> +            synchronize_rcu();
> >
> > I'm guessing you are forcing a synchronize_rcu() here because you are
> > free()'ing @old in the caller, yes?  Looking at the code, I only see
> > one caller, update_policy().  With only one caller, why not free @old
> > directly in ipe_update_policy()?  Do you see others callers that would
> > do something different?
> >
> The call of synchronize_rcu() is because we are updating the current
> active policy so we need to set the new policy as active.

Unless I'm mistaken, a syncronize_rcu() call only ensures that the
current task will see the updated value by waiting until all current
RCU critical sections have finished.  Given the mutex involved here I
don't believe this is necessary, but please correct me if I'm wrong.
Fan Wu Feb. 5, 2024, 11:21 p.m. UTC | #4
On 2/5/2024 3:10 PM, Paul Moore wrote:
> On Mon, Feb 5, 2024 at 6:01 PM Fan Wu <wufan@linux.microsoft.com> wrote:
>> On 2/3/2024 2:25 PM, Paul Moore wrote:
>>> On Jan 30, 2024 Fan Wu <wufan@linux.microsoft.com> wrote:
>>>>
>>>> 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@linux.microsoft.com>
>>>> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
>>>> ---
>>>> v2:
>>>>     + Split evaluation loop, access control hooks,
>>>>       and evaluation loop from policy parser and userspace
>>>>       interface to pass mailing list character limit
>>>>
>>>> v3:
>>>>     + Move policy load and activation audit event to 03/12
>>>>     + Fix a potential panic when a policy failed to load.
>>>>     + use pr_warn for a failure to parse instead of an
>>>>       audit record
>>>>     + Remove comments from headers
>>>>     + Add lockdep assertions to ipe_update_active_policy and
>>>>       ipe_activate_policy
>>>>     + Fix up warnings with checkpatch --strict
>>>>     + Use file_ns_capable for CAP_MAC_ADMIN for securityfs
>>>>       nodes.
>>>>     + Use memdup_user instead of kzalloc+simple_write_to_buffer.
>>>>     + Remove strict_parse command line parameter, as it is added
>>>>       by the sysctl command line.
>>>>     + Prefix extern variables with ipe_
>>>>
>>>> v4:
>>>>     + Remove securityfs to reverse-dependency
>>>>     + Add SHA1 reverse dependency.
>>>>     + Add versioning scheme for IPE properties, and associated
>>>>       interface to query the versioning scheme.
>>>>     + Cause a parser to always return an error on unknown syntax.
>>>>     + Remove strict_parse option
>>>>     + Change active_policy interface from sysctl, to securityfs,
>>>>       and change scheme.
>>>>
>>>> v5:
>>>>     + Cause an error if a default action is not defined for each
>>>>       operation.
>>>>     + Minor function renames
>>>>
>>>> v6:
>>>>     + No changes
>>>>
>>>> v7:
>>>>     + Propagating changes to support the new ipe_context structure in the
>>>>       evaluation loop.
>>>>
>>>>     + Further split the parser and userspace interface changes into
>>>>       separate commits.
>>>>
>>>>     + "raw" was renamed to "pkcs7" and made read only
>>>>     + "raw"'s write functionality (update a policy) moved to "update"
>>>>     + introduced "version", "policy_name" nodes.
>>>>     + "content" renamed to "policy"
>>>>     + changes to allow the compiled-in policy to be treated
>>>>       identical to deployed-after-the-fact policies.
>>>>
>>>> v8:
>>>>     + Prevent securityfs initialization if the LSM is disabled
>>>>
>>>> v9:
>>>>     + Switch to securityfs_recursive_remove for policy folder deletion
>>>>
>>>> v10:
>>>>     + Simplify and correct concurrency
>>>>     + Fix typos
>>>>
>>>> v11:
>>>>     + Correct code comments
>>>>
>>>> v12:
>>>>     + Correct locking and remove redundant code
>>>> ---
>>>>    security/ipe/Makefile    |   2 +
>>>>    security/ipe/fs.c        | 101 +++++++++
>>>>    security/ipe/fs.h        |  16 ++
>>>>    security/ipe/ipe.c       |   3 +
>>>>    security/ipe/ipe.h       |   2 +
>>>>    security/ipe/policy.c    | 123 ++++++++++
>>>>    security/ipe/policy.h    |   9 +
>>>>    security/ipe/policy_fs.c | 469 +++++++++++++++++++++++++++++++++++++++
>>>>    8 files changed, 725 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 f22a576a6d68..61fea3e38e11 100644
>>>> --- a/security/ipe/policy.c
>>>> +++ b/security/ipe/policy.c
>>>> @@ -43,6 +71,68 @@ 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.
>>>> + * @root: Supplies a pointer to the securityfs inode saved the 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.
>>>> + *
>>>> + * Context: Requires root->i_rwsem to be held.
>>>> + * Return:
>>>> + * * !IS_ERR        - The existing policy saved in the inode before update
>>>> + * * -ENOENT        - Policy doesn't exist
>>>> + * * -EINVAL        - New policy is invalid
>>>> + */
>>>> +struct ipe_policy *ipe_update_policy(struct inode *root,
>>>> +                                 const char *text, size_t textlen,
>>>> +                                 const char *pkcs7, size_t pkcs7len)
>>>> +{
>>>> +    int rc = 0;
>>>> +    struct ipe_policy *old, *ap, *new = NULL;
>>>> +
>>>> +    old = (struct ipe_policy *)root->i_private;
>>>> +    if (!old)
>>>> +            return ERR_PTR(-ENOENT);
>>>> +
>>>> +    new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
>>>> +    if (IS_ERR(new))
>>>> +            return new;
>>>> +
>>>> +    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;
>>>> +    }
>>>> +
>>>> +    root->i_private = new;
>>>> +    swap(new->policyfs, old->policyfs);
>>>
>>> Should the swap() take place with @ipe_policy_lock held?
>>>
>> I think we are safe here because root->i_rwsem is held. Other two
>> operations set_active and delete are also depending on the inode lock.
>>>> +    mutex_lock(&ipe_policy_lock);
>>>> +    ap = rcu_dereference_protected(ipe_active_policy,
>>>> +                                   lockdep_is_held(&ipe_policy_lock));
>>>> +    if (old == ap) {
>>>> +            rcu_assign_pointer(ipe_active_policy, new);
>>>> +            mutex_unlock(&ipe_policy_lock);
>>>> +            synchronize_rcu();
>>>
>>> I'm guessing you are forcing a synchronize_rcu() here because you are
>>> free()'ing @old in the caller, yes?  Looking at the code, I only see
>>> one caller, update_policy().  With only one caller, why not free @old
>>> directly in ipe_update_policy()?  Do you see others callers that would
>>> do something different?
>>>
>> The call of synchronize_rcu() is because we are updating the current
>> active policy so we need to set the new policy as active.
> 
> Unless I'm mistaken, a syncronize_rcu() call only ensures that the
> current task will see the updated value by waiting until all current
> RCU critical sections have finished.  Given the mutex involved here I
> don't believe this is necessary, but please correct me if I'm wrong.
> 
Sorry for the confusion. I think your previous comment was right, the 
call of synchronize_rcu() is to free the old one. And I should put the 
free of old just after the synchronize_rcu() call.

Thanks,
Fan
diff mbox series

Patch

diff --git a/security/ipe/Makefile b/security/ipe/Makefile
index d7f2870d7c09..cfbed03a8885 100644
--- a/security/ipe/Makefile
+++ b/security/ipe/Makefile
@@ -8,6 +8,8 @@ 
 obj-$(CONFIG_SECURITY_IPE) += \
 	eval.o \
 	hooks.o \
+	fs.o \
 	ipe.o \
 	policy.o \
+	policy_fs.o \
 	policy_parser.o \
diff --git a/security/ipe/fs.c b/security/ipe/fs.c
new file mode 100644
index 000000000000..4949296caeb5
--- /dev/null
+++ b/security/ipe/fs.c
@@ -0,0 +1,101 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/dcache.h>
+#include <linux/security.h>
+
+#include "ipe.h"
+#include "fs.h"
+#include "policy.h"
+
+static struct dentry *np __ro_after_init;
+static struct dentry *root __ro_after_init;
+struct dentry *policy_root __ro_after_init;
+
+/**
+ * new_policy - Write handler for the securityfs node, "ipe/new_policy".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t new_policy(struct file *f, const char __user *data,
+			  size_t len, loff_t *offset)
+{
+	int rc = 0;
+	char *copy = NULL;
+	struct ipe_policy *p = NULL;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	copy = memdup_user_nul(data, len);
+	if (IS_ERR(copy))
+		return PTR_ERR(copy);
+
+	p = ipe_new_policy(NULL, 0, copy, len);
+	if (IS_ERR(p)) {
+		rc = PTR_ERR(p);
+		goto out;
+	}
+
+	rc = ipe_new_policyfs_node(p);
+
+out:
+	if (rc < 0)
+		ipe_free_policy(p);
+	kfree(copy);
+	return (rc < 0) ? rc : len;
+}
+
+static const struct file_operations np_fops = {
+	.write = new_policy,
+};
+
+/**
+ * ipe_init_securityfs - Initialize IPE's securityfs tree at fsinit.
+ *
+ * Return:
+ * * !0	- Error
+ * * 0	- OK
+ */
+static int __init ipe_init_securityfs(void)
+{
+	int rc = 0;
+
+	if (!ipe_enabled)
+		return -EOPNOTSUPP;
+
+	root = securityfs_create_dir("ipe", NULL);
+	if (IS_ERR(root)) {
+		rc = PTR_ERR(root);
+		goto err;
+	}
+
+	policy_root = securityfs_create_dir("policies", root);
+	if (IS_ERR(policy_root)) {
+		rc = PTR_ERR(policy_root);
+		goto err;
+	}
+
+	np = securityfs_create_file("new_policy", 0200, root, NULL, &np_fops);
+	if (IS_ERR(np)) {
+		rc = PTR_ERR(np);
+		goto err;
+	}
+
+	return 0;
+err:
+	securityfs_remove(np);
+	securityfs_remove(policy_root);
+	securityfs_remove(root);
+	return rc;
+}
+
+fs_initcall(ipe_init_securityfs);
diff --git a/security/ipe/fs.h b/security/ipe/fs.h
new file mode 100644
index 000000000000..c1fc0ca4ae93
--- /dev/null
+++ b/security/ipe/fs.h
@@ -0,0 +1,16 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#ifndef _IPE_FS_H
+#define _IPE_FS_H
+
+#include "policy.h"
+
+extern struct dentry *policy_root __ro_after_init;
+
+int ipe_new_policyfs_node(struct ipe_policy *p);
+void ipe_del_policyfs_node(struct ipe_policy *p);
+
+#endif /* _IPE_FS_H */
diff --git a/security/ipe/ipe.c b/security/ipe/ipe.c
index ed3acf6174d8..034ee8cd6802 100644
--- a/security/ipe/ipe.c
+++ b/security/ipe/ipe.c
@@ -8,6 +8,8 @@ 
 #include "eval.h"
 #include "hooks.h"
 
+bool ipe_enabled;
+
 static struct lsm_blob_sizes ipe_blobs __ro_after_init = {
 #ifdef CONFIG_BLK_DEV_INITRD
 	.lbs_superblock = sizeof(struct ipe_sb),
@@ -50,6 +52,7 @@  static struct security_hook_list ipe_hooks[] __ro_after_init = {
 static int __init ipe_init(void)
 {
 	security_add_hooks(ipe_hooks, ARRAY_SIZE(ipe_hooks), &ipe_lsmid);
+	ipe_enabled = true;
 
 	return 0;
 }
diff --git a/security/ipe/ipe.h b/security/ipe/ipe.h
index f1e7c3222b6d..1862c710dab8 100644
--- a/security/ipe/ipe.h
+++ b/security/ipe/ipe.h
@@ -16,4 +16,6 @@ 
 struct ipe_sb *ipe_sb(const struct super_block *sb);
 #endif /* CONFIG_BLK_DEV_INITRD */
 
+extern bool ipe_enabled;
+
 #endif /* _IPE_H */
diff --git a/security/ipe/policy.c b/security/ipe/policy.c
index f22a576a6d68..61fea3e38e11 100644
--- a/security/ipe/policy.c
+++ b/security/ipe/policy.c
@@ -7,9 +7,36 @@ 
 #include <linux/verification.h>
 
 #include "ipe.h"
+#include "eval.h"
+#include "fs.h"
 #include "policy.h"
 #include "policy_parser.h"
 
+/* lock for synchronizing writers across ipe policy */
+DEFINE_MUTEX(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;
+
+	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);
 	/*
 	 * p->text is allocated only when p->pkcs7 is not NULL
@@ -43,6 +71,68 @@  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.
+ * @root: Supplies a pointer to the securityfs inode saved the 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.
+ *
+ * Context: Requires root->i_rwsem to be held.
+ * Return:
+ * * !IS_ERR	- The existing policy saved in the inode before update
+ * * -ENOENT	- Policy doesn't exist
+ * * -EINVAL	- New policy is invalid
+ */
+struct ipe_policy *ipe_update_policy(struct inode *root,
+				     const char *text, size_t textlen,
+				     const char *pkcs7, size_t pkcs7len)
+{
+	int rc = 0;
+	struct ipe_policy *old, *ap, *new = NULL;
+
+	old = (struct ipe_policy *)root->i_private;
+	if (!old)
+		return ERR_PTR(-ENOENT);
+
+	new = ipe_new_policy(text, textlen, pkcs7, pkcs7len);
+	if (IS_ERR(new))
+		return new;
+
+	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;
+	}
+
+	root->i_private = new;
+	swap(new->policyfs, old->policyfs);
+
+	mutex_lock(&ipe_policy_lock);
+	ap = rcu_dereference_protected(ipe_active_policy,
+				       lockdep_is_held(&ipe_policy_lock));
+	if (old == ap) {
+		rcu_assign_pointer(ipe_active_policy, new);
+		mutex_unlock(&ipe_policy_lock);
+		synchronize_rcu();
+	} else {
+		mutex_unlock(&ipe_policy_lock);
+	}
+
+	return old;
+err:
+	ipe_free_policy(new);
+	return ERR_PTR(rc);
+}
+
 /**
  * ipe_new_policy - Allocate and parse an ipe_policy structure.
  *
@@ -99,3 +189,36 @@  struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
 	ipe_free_policy(new);
 	return ERR_PTR(rc);
 }
+
+/**
+ * ipe_set_active_pol - Make @p the active policy.
+ * @p: Supplies a pointer to the policy to make active.
+ *
+ * Context: Requires root->i_rwsem, which i_private has the policy, to be held.
+ * Return:
+ * * !IS_ERR	- Success
+ * * -EINVAL	- New active policy version is invalid
+ */
+int ipe_set_active_pol(const struct ipe_policy *p)
+{
+	struct ipe_policy *ap = NULL;
+
+	mutex_lock(&ipe_policy_lock);
+
+	ap = rcu_dereference_protected(ipe_active_policy,
+				       lockdep_is_held(&ipe_policy_lock));
+	if (ap == p) {
+		mutex_unlock(&ipe_policy_lock);
+		return 0;
+	}
+	if (ap && ver_to_u64(ap) > ver_to_u64(p)) {
+		mutex_unlock(&ipe_policy_lock);
+		return -EINVAL;
+	}
+
+	rcu_assign_pointer(ipe_active_policy, p);
+	mutex_unlock(&ipe_policy_lock);
+	synchronize_rcu();
+
+	return 0;
+}
diff --git a/security/ipe/policy.h b/security/ipe/policy.h
index fb48024bb63e..060ffdbc62d6 100644
--- a/security/ipe/policy.h
+++ b/security/ipe/policy.h
@@ -7,6 +7,7 @@ 
 
 #include <linux/list.h>
 #include <linux/types.h>
+#include <linux/fs.h>
 
 enum ipe_op_type {
 	IPE_OP_EXEC = 0,
@@ -76,10 +77,18 @@  struct ipe_policy {
 	size_t textlen;
 
 	struct ipe_parsed_policy *parsed;
+
+	struct dentry *policyfs;
 };
 
 struct ipe_policy *ipe_new_policy(const char *text, size_t textlen,
 				  const char *pkcs7, size_t pkcs7len);
 void ipe_free_policy(struct ipe_policy *pol);
+struct ipe_policy *ipe_update_policy(struct inode *root,
+				     const char *text,
+				     size_t textlen, const char *pkcs7,
+				     size_t pkcs7len);
+int ipe_set_active_pol(const struct ipe_policy *p);
+extern struct mutex ipe_policy_lock;
 
 #endif /* _IPE_POLICY_H */
diff --git a/security/ipe/policy_fs.c b/security/ipe/policy_fs.c
new file mode 100644
index 000000000000..abdf1ad843e0
--- /dev/null
+++ b/security/ipe/policy_fs.c
@@ -0,0 +1,469 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/types.h>
+#include <linux/dcache.h>
+#include <linux/security.h>
+
+#include "ipe.h"
+#include "policy.h"
+#include "eval.h"
+#include "fs.h"
+
+#define MAX_VERSION_SIZE ARRAY_SIZE("65535.65535.65535")
+
+/**
+ * ipefs_file - defines a file in securityfs.
+ */
+struct ipefs_file {
+	const char *name;
+	umode_t access;
+	const struct file_operations *fops;
+};
+
+/**
+ * read_pkcs7 - Read handler for "ipe/policies/$name/pkcs7".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * @data will be populated with the pkcs7 blob representing the policy
+ * on success. If the policy is unsigned (like the boot policy), this
+ * will return -ENOENT.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t read_pkcs7(struct file *f, char __user *data,
+			  size_t len, loff_t *offset)
+{
+	int rc = 0;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+
+	inode_lock_shared(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	if (!p->pkcs7) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	rc = simple_read_from_buffer(data, len, offset, p->pkcs7, p->pkcs7len);
+
+out:
+	inode_unlock_shared(root);
+
+	return rc;
+}
+
+/**
+ * read_policy - Read handler for "ipe/policies/$name/policy".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * @data will be populated with the plain-text version of the policy
+ * on success.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t read_policy(struct file *f, char __user *data,
+			   size_t len, loff_t *offset)
+{
+	int rc = 0;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+
+	inode_lock_shared(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	rc = simple_read_from_buffer(data, len, offset, p->text, p->textlen);
+
+out:
+	inode_unlock_shared(root);
+
+	return rc;
+}
+
+/**
+ * read_name: Read handler for "ipe/policies/$name/name".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * @data will be populated with the policy_name attribute on success.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t read_name(struct file *f, char __user *data,
+			 size_t len, loff_t *offset)
+{
+	int rc = 0;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+
+	inode_lock_shared(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	rc = simple_read_from_buffer(data, len, offset, p->parsed->name,
+				     strlen(p->parsed->name));
+
+out:
+	inode_unlock_shared(root);
+
+	return rc;
+}
+
+/**
+ * read_version - Read handler for "ipe/policies/$name/version".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * @data will be populated with the version string on success.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t read_version(struct file *f, char __user *data,
+			    size_t len, loff_t *offset)
+{
+	ssize_t rc = 0;
+	size_t strsize = 0;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+	char buffer[MAX_VERSION_SIZE] = { 0 };
+
+	root = d_inode(f->f_path.dentry->d_parent);
+
+	inode_lock_shared(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	strsize = scnprintf(buffer, ARRAY_SIZE(buffer), "%hu.%hu.%hu",
+			    p->parsed->version.major, p->parsed->version.minor,
+			    p->parsed->version.rev);
+
+	rc = simple_read_from_buffer(data, len, offset, buffer, strsize);
+
+out:
+	inode_unlock_shared(root);
+
+	return rc;
+}
+
+/**
+ * setactive - Write handler for "ipe/policies/$name/active".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t setactive(struct file *f, const char __user *data,
+			 size_t len, loff_t *offset)
+{
+	int rc = 0;
+	bool value = false;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	rc = kstrtobool_from_user(data, len, &value);
+	if (rc)
+		return rc;
+
+	if (!value)
+		return -EINVAL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+	inode_lock(root);
+
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		rc = -ENOENT;
+		goto out;
+	}
+
+	rc = ipe_set_active_pol(p);
+
+out:
+	inode_unlock(root);
+	return (rc < 0) ? rc : len;
+}
+
+/**
+ * getactive - Read handler for "ipe/policies/$name/active".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * @data will be populated with the 1 or 0 depending on if the
+ * corresponding policy is active.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t getactive(struct file *f, char __user *data,
+			 size_t len, loff_t *offset)
+{
+	int rc = 0;
+	const char *str;
+	struct inode *root = NULL;
+	const struct ipe_policy *p = NULL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+
+	inode_lock_shared(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		inode_unlock_shared(root);
+		return -ENOENT;
+	}
+	inode_unlock_shared(root);
+
+	str = (p == rcu_access_pointer(ipe_active_policy)) ? "1" : "0";
+	rc = simple_read_from_buffer(data, len, offset, str, 1);
+
+	return rc;
+}
+
+/**
+ * update_policy - Write handler for "ipe/policies/$name/update".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * On success this updates the policy represented by $name,
+ * in-place.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t update_policy(struct file *f, const char __user *data,
+			     size_t len, loff_t *offset)
+{
+	char *copy = NULL;
+	struct inode *root = NULL;
+	struct ipe_policy *old = NULL;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	copy = memdup_user(data, len);
+	if (IS_ERR(copy))
+		return PTR_ERR(copy);
+
+	root = d_inode(f->f_path.dentry->d_parent);
+	inode_lock(root);
+	old = ipe_update_policy(root, NULL, 0, copy, len);
+	inode_unlock(root);
+
+	kfree(copy);
+	if (IS_ERR(old))
+		return PTR_ERR(old);
+	ipe_free_policy(old);
+
+	return len;
+}
+
+/**
+ * delete_policy - write handler for  "ipe/policies/$name/delete".
+ * @f: Supplies a file structure representing the securityfs node.
+ * @data: Supplies a buffer passed to the write syscall.
+ * @len: Supplies the length of @data.
+ * @offset: unused.
+ *
+ * On success this deletes the policy represented by $name.
+ *
+ * Return:
+ * * >0	- Success, Length of buffer written
+ * * <0	- Error
+ */
+static ssize_t delete_policy(struct file *f, const char __user *data,
+			     size_t len, loff_t *offset)
+{
+	int rc = 0;
+	bool value = false;
+	struct inode *root = NULL;
+	struct ipe_policy *p = NULL;
+	struct ipe_policy *ap = NULL;
+
+	if (!file_ns_capable(f, &init_user_ns, CAP_MAC_ADMIN))
+		return -EPERM;
+
+	rc = kstrtobool_from_user(data, len, &value);
+	if (rc)
+		return rc;
+
+	if (!value)
+		return -EINVAL;
+
+	root = d_inode(f->f_path.dentry->d_parent);
+	inode_lock(root);
+	p = (struct ipe_policy *)root->i_private;
+	if (!p) {
+		inode_unlock(root);
+		return -ENOENT;
+	}
+
+	mutex_lock(&ipe_policy_lock);
+	ap = rcu_dereference_protected(ipe_active_policy,
+				       lockdep_is_held(&ipe_policy_lock));
+	if (p == ap) {
+		mutex_unlock(&ipe_policy_lock);
+		inode_unlock(root);
+		return -EPERM;
+	}
+	mutex_unlock(&ipe_policy_lock);
+
+	root->i_private = NULL;
+	inode_unlock(root);
+
+	ipe_free_policy(p);
+	return len;
+}
+
+static const struct file_operations content_fops = {
+	.read = read_policy,
+};
+
+static const struct file_operations pkcs7_fops = {
+	.read = read_pkcs7,
+};
+
+static const struct file_operations name_fops = {
+	.read = read_name,
+};
+
+static const struct file_operations ver_fops = {
+	.read = read_version,
+};
+
+static const struct file_operations active_fops = {
+	.write = setactive,
+	.read = getactive,
+};
+
+static const struct file_operations update_fops = {
+	.write = update_policy,
+};
+
+static const struct file_operations delete_fops = {
+	.write = delete_policy,
+};
+
+/**
+ * policy_subdir - files under a policy subdirectory
+ */
+static const struct ipefs_file policy_subdir[] = {
+	{ "pkcs7", 0444, &pkcs7_fops },
+	{ "policy", 0444, &content_fops },
+	{ "name", 0444, &name_fops },
+	{ "version", 0444, &ver_fops },
+	{ "active", 0600, &active_fops },
+	{ "update", 0200, &update_fops },
+	{ "delete", 0200, &delete_fops },
+};
+
+/**
+ * ipe_del_policyfs_node - Delete a securityfs entry for @p.
+ * @p: Supplies a pointer to the policy to delete a securityfs entry for.
+ */
+void ipe_del_policyfs_node(struct ipe_policy *p)
+{
+	securityfs_recursive_remove(p->policyfs);
+	p->policyfs = NULL;
+}
+
+/**
+ * ipe_new_policyfs_node - Create a securityfs entry for @p.
+ * @p: Supplies a pointer to the policy to create a securityfs entry for.
+ *
+ * Return:
+ * * 0	- OK
+ * * !0	- Error
+ */
+int ipe_new_policyfs_node(struct ipe_policy *p)
+{
+	int rc = 0;
+	size_t i = 0;
+	struct dentry *d = NULL;
+	struct dentry *policyfs = NULL;
+	struct inode *root = NULL;
+	const struct ipefs_file *f = NULL;
+
+	if (p->policyfs)
+		return 0;
+
+	policyfs = securityfs_create_dir(p->parsed->name, policy_root);
+	if (IS_ERR(policyfs))
+		return PTR_ERR(policyfs);
+
+	root = d_inode(policyfs);
+
+	for (i = 0; i < ARRAY_SIZE(policy_subdir); ++i) {
+		f = &policy_subdir[i];
+
+		d = securityfs_create_file(f->name, f->access, policyfs,
+					   NULL, f->fops);
+		if (IS_ERR(d)) {
+			rc = PTR_ERR(d);
+			goto err;
+		}
+	}
+
+	inode_lock(root);
+	p->policyfs = policyfs;
+	root->i_private = p;
+	inode_unlock(root);
+
+	return 0;
+err:
+	securityfs_recursive_remove(policyfs);
+	return rc;
+}