[PATCH 1/2] security: Add a cred_getsecid hook

[Casey Schaufler]

On 10/19/2017 4:14 PM, Matthew Garrett wrote:
> For IMA purposes, we want to be able to obtain the prepared secid in the
> bprm structure before the credentials are committed. Add a cred_getsecid
> hook that makes this possible.
>
> Signed-off-by: Matthew Garrett <mjg59 at google.com>
> Cc: Paul Moore <paul at paul-moore.com>
> Cc: Stephen Smalley <sds at tycho.nsa.gov>
> Cc: Eric Paris <eparis at parisplace.org>
> Cc: selinux at tycho.nsa.gov
> Cc: Casey Schaufler <casey at schaufler-ca.com>
> Cc: linux-security-module at vger.kernel.org
> Cc: Mimi Zohar <zohar at linux.vnet.ibm.com>
> Cc: Dmitry Kasatkin <dmitry.kasatkin at gmail.com>
> Cc: linux-integrity at vger.kernel.org
> ---
>  V2: incorporate Casey's requested change
>
>  include/linux/lsm_hooks.h  |  6 ++++++
>  include/linux/security.h   |  1 +
>  security/security.c        |  7 +++++++
>  security/selinux/hooks.c   |  8 ++++++++
>  security/smack/smack_lsm.c | 15 +++++++++++++++
>  5 files changed, 37 insertions(+)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index c9258124e417..c28c6f8b65dc 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -554,6 +554,10 @@
>   *	@new points to the new credentials.
>   *	@old points to the original credentials.
>   *	Transfer data from original creds to new creds
> + * @cred_getsecid:
> + *	Retrieve the security identifier of the cred structure @c
> + *	@c contains the credentials, secid will be placed into @secid.
> + *	In case of failure, @secid will be set to zero.
>   * @kernel_act_as:
>   *	Set the credentials for a kernel service to act as (subjective context).
>   *	@new points to the credentials to be modified.
> @@ -1507,6 +1511,7 @@ union security_list_options {
>  	int (*cred_prepare)(struct cred *new, const struct cred *old,
>  				gfp_t gfp);
>  	void (*cred_transfer)(struct cred *new, const struct cred *old);
> +	void (*cred_getsecid)(const struct cred *c, u32 *secid);
>  	int (*kernel_act_as)(struct cred *new, u32 secid);
>  	int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
>  	int (*kernel_module_request)(char *kmod_name);
> @@ -1779,6 +1784,7 @@ struct security_hook_heads {
>  	struct list_head cred_free;
>  	struct list_head cred_prepare;
>  	struct list_head cred_transfer;
> +	struct list_head cred_getsecid;
>  	struct list_head kernel_act_as;
>  	struct list_head kernel_create_files_as;
>  	struct list_head kernel_read_file;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index ce6265960d6c..14848fef8f62 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -324,6 +324,7 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp);
>  void security_cred_free(struct cred *cred);
>  int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
>  void security_transfer_creds(struct cred *new, const struct cred *old);
> +void security_cred_getsecid(const struct cred *c, u32 *secid);
>  int security_kernel_act_as(struct cred *new, u32 secid);
>  int security_kernel_create_files_as(struct cred *new, struct inode *inode);
>  int security_kernel_module_request(char *kmod_name);
> diff --git a/security/security.c b/security/security.c
> index 4bf0f571b4ef..02d217597400 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1004,6 +1004,13 @@ void security_transfer_creds(struct cred *new, const struct cred *old)
>  	call_void_hook(cred_transfer, new, old);
>  }
>  
> +void security_cred_getsecid(const struct cred *c, u32 *secid)
> +{
> +	*secid = 0;
> +	call_void_hook(cred_getsecid, c, secid);
> +}
> +EXPORT_SYMBOL(security_cred_getsecid);
> +
>  int security_kernel_act_as(struct cred *new, u32 secid)
>  {
>  	return call_int_hook(kernel_act_as, 0, new, secid);
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f5d304736852..1d11679674a6 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3836,6 +3836,13 @@ static void selinux_cred_transfer(struct cred *new, const struct cred *old)
>  	*tsec = *old_tsec;
>  }
>  
> +static void selinux_cred_getsecid(const struct cred *c, u32 *secid)
> +{
> +	rcu_read_lock();
> +	*secid = cred_sid(c);
> +	rcu_read_unlock();
> +}
> +
>  /*
>   * set the security data for a kernel service
>   * - all the creation contexts are set to unlabelled
> @@ -6338,6 +6345,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(cred_free, selinux_cred_free),
>  	LSM_HOOK_INIT(cred_prepare, selinux_cred_prepare),
>  	LSM_HOOK_INIT(cred_transfer, selinux_cred_transfer),
> +	LSM_HOOK_INIT(cred_getsecid, selinux_cred_getsecid),
>  	LSM_HOOK_INIT(kernel_act_as, selinux_kernel_act_as),
>  	LSM_HOOK_INIT(kernel_create_files_as, selinux_kernel_create_files_as),
>  	LSM_HOOK_INIT(kernel_module_request, selinux_kernel_module_request),
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 286171a16ed2..ed1bbf201e2f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2049,6 +2049,20 @@ static void smack_cred_transfer(struct cred *new, const struct cred *old)
>  	/* cbs copy rule list */
>  }
>  
> +/**
> + * smack_cred_getsecid - get the secid corresponding to a creds structure
> + * @c: the object creds
> + * @secid: where to put the result
> + *
> + * Sets the secid to contain a u32 version of the smack label.
> + */
> +static void smack_cred_getsecid(const struct cred *c, u32 *secid)
> +{
> +	rcu_read_lock();
> +	*secid = smk_of_task(c->security);
> +	rcu_read_unlock();
> +}
> +

smk_of_task does not return a u32, it returns a pointer to a
struct smack_known. You want

	+static void smack_cred_getsecid(const struct cred *cred, u32 *secid)
	+{
	+	struct smack_known *skp;
	+
	+	rcu_read_lock();
	+	skp = smk_of_task(cred->security);
	+	*secid = skp->smk_secid;
	+	rcu_read_unlock();
	+}

>  /**
>   * smack_kernel_act_as - Set the subjective context in a set of credentials
>   * @new: points to the set of credentials to be modified.
> @@ -4651,6 +4665,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(cred_free, smack_cred_free),
>  	LSM_HOOK_INIT(cred_prepare, smack_cred_prepare),
>  	LSM_HOOK_INIT(cred_transfer, smack_cred_transfer),
> +	LSM_HOOK_INIT(cred_getsecid, smack_cred_getsecid),
>  	LSM_HOOK_INIT(kernel_act_as, smack_kernel_act_as),
>  	LSM_HOOK_INIT(kernel_create_files_as, smack_kernel_create_files_as),
>  	LSM_HOOK_INIT(task_setpgid, smack_task_setpgid),

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