[PATCH 1/2] security: Add a cred_getsecid hook
Casey Schaufler
casey at schaufler-ca.com
Mon Oct 16 21:58:05 UTC 2017
On 10/16/2017 1:37 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.
Why do you want the secid? What are you planning to do with it?
>
> 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
> ---
> include/linux/lsm_hooks.h | 6 ++++++
> include/linux/security.h | 1 +
> security/security.c | 7 +++++++
> security/selinux/hooks.c | 8 ++++++++
> security/smack/smack.h | 10 ++++++++++
> security/smack/smack_lsm.c | 14 ++++++++++++++
> 6 files changed, 46 insertions(+)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index ce02f76a6188..48a929fd47e6 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -556,6 +556,10 @@
> * @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
> + * @p 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.
> @@ -1510,6 +1514,7 @@ 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);
> @@ -1783,6 +1788,7 @@ 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 458e24bea2d4..8d969958c25e 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 55b5997e4b72..0f5784880c94 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1009,6 +1009,13 @@ 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 33fd061305c4..e0828e9130c7 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3829,6 +3829,13 @@ 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
> @@ -6332,6 +6339,7 @@ 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.h b/security/smack/smack.h
> index 6a71fc7831ab..5af7b7e709bc 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -391,6 +391,16 @@ static inline struct smack_known *smk_of_task_struct(const struct task_struct *t
> return skp;
> }
>
> +static inline struct smack_known *smk_of_cred(const struct cred *c)
> +{
> + struct smack_known *skp;
> +
> + rcu_read_lock();
> + skp = smk_of_task(c->security);
> + rcu_read_unlock();
> + return skp;
> +}
> +
Don't put a one-use function in the header file. Code it
directly in smack_cred_getsecid(). You're doubling the size
of the code and obscuring it doing it this way.
> /*
> * Present a pointer to the forked smack label entry in an task blob.
> */
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 463af86812c7..f1710cf76f7f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2080,6 +2080,19 @@ 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)
> +{
> + struct smack_known *skp = smk_of_cred(c);
> + *secid = skp->smk_secid;
> +}
> +
> /**
> * smack_kernel_act_as - Set the subjective context in a set of credentials
> * @new: points to the set of credentials to be modified.
> @@ -4684,6 +4697,7 @@ 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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