[PATCH v39 13/42] LSM: Create new security_cred_getlsmblob LSM hook

[Casey Schaufler]

Create a new LSM hook security_cred_getlsmblob() which, like
security_cred_getsecid(), fetches LSM specific attributes from the
cred structure.  The associated data elements in the audit sub-system
are changed from a secid to a lsmblob to accommodate multiple possible
LSM audit users.

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
Acked-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Cc: linux-integrity@xxxxxxxxxxxxxxx
Cc: audit@xxxxxxxxxxxxxxx
Cc: Todd Kjos <tkjos@xxxxxxxxxx>
---
 include/linux/lsm_hook_defs.h     |  2 ++
 include/linux/security.h          |  7 +++++++
 security/integrity/ima/ima_main.c |  7 ++-----
 security/security.c               | 15 +++++++++++++++
 security/selinux/hooks.c          |  8 ++++++++
 security/smack/smack_lsm.c        | 18 ++++++++++++++++++
 6 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 3c51ee8e3d6c..fe9c1d89dc66 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -196,6 +196,8 @@ LSM_HOOK(int, 0, cred_prepare, struct cred *new, const struct cred *old,
 LSM_HOOK(void, LSM_RET_VOID, cred_transfer, struct cred *new,
 	 const struct cred *old)
 LSM_HOOK(void, LSM_RET_VOID, cred_getsecid, const struct cred *c, u32 *secid)
+LSM_HOOK(void, LSM_RET_VOID, cred_getlsmblob, const struct cred *c,
+	 struct lsmblob *blob)
 LSM_HOOK(int, 0, kernel_act_as, struct cred *new, u32 secid)
 LSM_HOOK(int, 0, kernel_create_files_as, struct cred *new, struct inode *inode)
 LSM_HOOK(int, 0, kernel_module_request, char *kmod_name)
diff --git a/include/linux/security.h b/include/linux/security.h
index e8b7f858de04..67ecf8588c90 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -460,6 +460,7 @@ 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);
+void security_cred_getlsmblob(const struct cred *c, struct lsmblob *blob);
 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);
@@ -1151,6 +1152,12 @@ static inline void security_cred_getsecid(const struct cred *c, u32 *secid)
 	*secid = 0;
 }
 
+static inline void security_cred_getlsmblob(const struct cred *c,
+					    struct lsmblob *blob)
+{
+	*secid = 0;
+}
+
 static inline int security_kernel_act_as(struct cred *cred, u32 secid)
 {
 	return 0;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 657143fe558d..c69eb9665cc1 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -526,8 +526,7 @@ int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
 int ima_bprm_check(struct linux_binprm *bprm)
 {
 	int ret;
-	u32 secid;
-	struct lsmblob blob = { };
+	struct lsmblob blob;
 
 	security_current_getlsmblob_subj(&blob);
 	ret = process_measurement(bprm->file, current_cred(),
@@ -535,9 +534,7 @@ int ima_bprm_check(struct linux_binprm *bprm)
 	if (ret)
 		return ret;
 
-	security_cred_getsecid(bprm->cred, &secid);
-	/* stacking scaffolding */
-	blob.scaffold.secid = secid;
+	security_cred_getlsmblob(bprm->cred, &blob);
 	return process_measurement(bprm->file, bprm->cred, &blob, NULL, 0,
 				   MAY_EXEC, CREDS_CHECK);
 }
diff --git a/security/security.c b/security/security.c
index ed4e9b5fdf70..1cbd45310f63 100644
--- a/security/security.c
+++ b/security/security.c
@@ -3111,6 +3111,21 @@ void security_cred_getsecid(const struct cred *c, u32 *secid)
 }
 EXPORT_SYMBOL(security_cred_getsecid);
 
+/**
+ * security_cred_getlsmblob() - Get the LSM data from a set of credentials
+ * @c: credentials
+ * @blob: destination for the LSM data
+ *
+ * Retrieve the security data of the cred structure @c.  In case of
+ * failure, @blob will be cleared.
+ */
+void security_cred_getlsmblob(const struct cred *c, struct lsmblob *blob)
+{
+	lsmblob_init(blob);
+	call_void_hook(cred_getlsmblob, c, blob);
+}
+EXPORT_SYMBOL(security_cred_getlsmblob);
+
 /**
  * security_kernel_act_as() - Set the kernel credentials to act as secid
  * @new: credentials
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 4ab923698da9..1bc28f5f6870 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3992,6 +3992,13 @@ static void selinux_cred_getsecid(const struct cred *c, u32 *secid)
 	*secid = cred_sid(c);
 }
 
+static void selinux_cred_getlsmblob(const struct cred *c, struct lsmblob *blob)
+{
+	blob->selinux.secid = cred_sid(c);
+	/* stacking scaffolding */
+	blob->scaffold.secid = blob->selinux.secid;
+}
+
 /*
  * set the security data for a kernel service
  * - all the creation contexts are set to unlabelled
@@ -7153,6 +7160,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 	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(cred_getlsmblob, selinux_cred_getlsmblob),
 	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 e6d49e59a0c0..7dab00bbd0ed 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2121,6 +2121,23 @@ static void smack_cred_getsecid(const struct cred *cred, u32 *secid)
 	rcu_read_unlock();
 }
 
+/**
+ * smack_cred_getlsmblob - get the Smack label for a creds structure
+ * @cred: the object creds
+ * @blob: where to put the data
+ *
+ * Sets the Smack part of the blob
+ */
+static void smack_cred_getlsmblob(const struct cred *cred,
+				  struct lsmblob *blob)
+{
+	rcu_read_lock();
+	blob->smack.skp = smk_of_task(smack_cred(cred));
+	/* stacking scaffolding */
+	blob->scaffold.secid = blob->smack.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.
@@ -5102,6 +5119,7 @@ static struct security_hook_list smack_hooks[] __ro_after_init = {
 	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(cred_getlsmblob, smack_cred_getlsmblob),
 	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),
-- 
2.41.0