On Thu, 2017-10-26 at 01:40 -0700, Matthew Garrett via Selinux 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@xxxxxxxxxx>
> Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
> Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
> Cc: Eric Paris <eparis@xxxxxxxxxxxxxx>
> Cc: selinux@xxxxxxxxxxxxx
> Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Cc: linux-security-module@xxxxxxxxxxxxxxx
> Cc: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
> Cc: linux-integrity@xxxxxxxxxxxxxxx
> ---
> V3: Fix smack_cred_getsecid()
>
> 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 | 18 ++++++++++++++++++
> 5 files changed, 40 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();
Is rcu_read_lock() necessary here? Seems like we use cred_sid() in many
places without it.
> +}
> +
> /*
> * 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..37c35aaa6955 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2049,6 +2049,23 @@ 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;
> +
> + rcu_read_lock();
> + skp = smk_of_task(c->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 +4668,7 @@ 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),
