lsm: security_task_getsecid_subj() -> security_current_getsecid_subj()

The security_task_getsecid_subj() LSM hook invites misuse by allowing callers to specify a task even though the hook is only safe when the current task is referenced. Fix this by removing the task_struct argument to the hook, requiring LSM implementations to use the current task. While we are changing the hook declaration we also rename the function to security_current_getsecid_subj() in an effort to reinforce that the hook captures the subjective credentials of the current task and not an arbitrary task on the system. Reviewed-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Paul Moore <paul@paul-moore.com>
mariobalanica · Nov 22, 2021 · 6326948 · 6326948
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diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
@@ -206,8 +206,7 @@ LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
 LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
 LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
 LSM_HOOK(int, 0, task_getsid, struct task_struct *p)
-LSM_HOOK(void, LSM_RET_VOID, task_getsecid_subj,
-	 struct task_struct *p, u32 *secid)
+LSM_HOOK(void, LSM_RET_VOID, current_getsecid_subj, u32 *secid)
 LSM_HOOK(void, LSM_RET_VOID, task_getsecid_obj,
 	 struct task_struct *p, u32 *secid)
 LSM_HOOK(int, 0, task_setnice, struct task_struct *p, int nice)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
@@ -719,11 +719,9 @@
  *	@p.
  *	@p contains the task_struct for the process.
  *	Return 0 if permission is granted.
- * @task_getsecid_subj:
- *	Retrieve the subjective security identifier of the task_struct in @p
- *	and return it in @secid.  Special care must be taken to ensure that @p
- *	is the either the "current" task, or the caller has exclusive access
- *	to @p.
+ * @current_getsecid_subj:
+ *	Retrieve the subjective security identifier of the current task and
+ *	return it in @secid.
  *	In case of failure, @secid will be set to zero.
  * @task_getsecid_obj:
  *	Retrieve the objective security identifier of the task_struct in @p

diff --git a/include/linux/security.h b/include/linux/security.h
@@ -418,7 +418,7 @@ int security_task_fix_setgid(struct cred *new, const struct cred *old,
 int security_task_setpgid(struct task_struct *p, pid_t pgid);
 int security_task_getpgid(struct task_struct *p);
 int security_task_getsid(struct task_struct *p);
-void security_task_getsecid_subj(struct task_struct *p, u32 *secid);
+void security_current_getsecid_subj(u32 *secid);
 void security_task_getsecid_obj(struct task_struct *p, u32 *secid);
 int security_task_setnice(struct task_struct *p, int nice);
 int security_task_setioprio(struct task_struct *p, int ioprio);
@@ -1119,7 +1119,7 @@ static inline int security_task_getsid(struct task_struct *p)
 	return 0;
 }
 
-static inline void security_task_getsecid_subj(struct task_struct *p, u32 *secid)
+static inline void security_current_getsecid_subj(u32 *secid)
 {
 	*secid = 0;
 }

diff --git a/kernel/audit.c b/kernel/audit.c
@@ -2132,7 +2132,7 @@ int audit_log_task_context(struct audit_buffer *ab)
 	int error;
 	u32 sid;
 
-	security_task_getsecid_subj(current, &sid);
+	security_current_getsecid_subj(&sid);
 	if (!sid)
 		return 0;
 
@@ -2353,7 +2353,7 @@ int audit_signal_info(int sig, struct task_struct *t)
 			audit_sig_uid = auid;
 		else
 			audit_sig_uid = uid;
-		security_task_getsecid_subj(current, &audit_sig_sid);
+		security_current_getsecid_subj(&audit_sig_sid);
 	}
 
 	return audit_signal_info_syscall(t);

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
@@ -1368,8 +1368,7 @@ int audit_filter(int msgtype, unsigned int listtype)
 			case AUDIT_SUBJ_SEN:
 			case AUDIT_SUBJ_CLR:
 				if (f->lsm_rule) {
-					security_task_getsecid_subj(current,
-								    &sid);
+					security_current_getsecid_subj(&sid);
 					result = security_audit_rule_match(sid,
 						   f->type, f->op, f->lsm_rule);
 				}

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
@@ -666,7 +666,16 @@ static int audit_filter_rules(struct task_struct *tsk,
 			   logged upon error */
 			if (f->lsm_rule) {
 				if (need_sid) {
-					security_task_getsecid_subj(tsk, &sid);
+					/* @tsk should always be equal to
+					 * @current with the exception of
+					 * fork()/copy_process() in which case
+					 * the new @tsk creds are still a dup
+					 * of @current's creds so we can still
+					 * use security_current_getsecid_subj()
+					 * here even though it always refs
+					 * @current's creds
+					 */
+					security_current_getsecid_subj(&sid);
 					need_sid = 0;
 				}
 				result = security_audit_rule_match(sid, f->type,

diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
@@ -1537,7 +1537,7 @@ int __init netlbl_unlabel_defconf(void)
 	/* Only the kernel is allowed to call this function and the only time
 	 * it is called is at bootup before the audit subsystem is reporting
 	 * messages so don't worry to much about these values. */
-	security_task_getsecid_subj(current, &audit_info.secid);
+	security_current_getsecid_subj(&audit_info.secid);
 	audit_info.loginuid = GLOBAL_ROOT_UID;
 	audit_info.sessionid = 0;
 

diff --git a/net/netlabel/netlabel_user.h b/net/netlabel/netlabel_user.h
@@ -32,7 +32,7 @@
  */
 static inline void netlbl_netlink_auditinfo(struct netlbl_audit *audit_info)
 {
-	security_task_getsecid_subj(current, &audit_info->secid);
+	security_current_getsecid_subj(&audit_info->secid);
 	audit_info->loginuid = audit_get_loginuid(current);
 	audit_info->sessionid = audit_get_sessionid(current);
 }

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
@@ -728,7 +728,14 @@ static void apparmor_bprm_committed_creds(struct linux_binprm *bprm)
 	return;
 }
 
-static void apparmor_task_getsecid(struct task_struct *p, u32 *secid)
+static void apparmor_current_getsecid_subj(u32 *secid)
+{
+	struct aa_label *label = aa_get_current_label();
+	*secid = label->secid;
+	aa_put_label(label);
+}
+
+static void apparmor_task_getsecid_obj(struct task_struct *p, u32 *secid)
 {
 	struct aa_label *label = aa_get_task_label(p);
 	*secid = label->secid;
@@ -1252,8 +1259,8 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
 
 	LSM_HOOK_INIT(task_free, apparmor_task_free),
 	LSM_HOOK_INIT(task_alloc, apparmor_task_alloc),
-	LSM_HOOK_INIT(task_getsecid_subj, apparmor_task_getsecid),
-	LSM_HOOK_INIT(task_getsecid_obj, apparmor_task_getsecid),
+	LSM_HOOK_INIT(current_getsecid_subj, apparmor_current_getsecid_subj),
+	LSM_HOOK_INIT(task_getsecid_obj, apparmor_task_getsecid_obj),
 	LSM_HOOK_INIT(task_setrlimit, apparmor_task_setrlimit),
 	LSM_HOOK_INIT(task_kill, apparmor_task_kill),
 

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
@@ -76,7 +76,7 @@ int ima_must_appraise(struct user_namespace *mnt_userns, struct inode *inode,
 	if (!ima_appraise)
 		return 0;
 
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	return ima_match_policy(mnt_userns, inode, current_cred(), secid,
 				func, mask, IMA_APPRAISE | IMA_HASH, NULL,
 				NULL, NULL, NULL);

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
@@ -408,7 +408,7 @@ int ima_file_mmap(struct file *file, unsigned long prot)
 	u32 secid;
 
 	if (file && (prot & PROT_EXEC)) {
-		security_task_getsecid_subj(current, &secid);
+		security_current_getsecid_subj(&secid);
 		return process_measurement(file, current_cred(), secid, NULL,
 					   0, MAY_EXEC, MMAP_CHECK);
 	}
@@ -446,7 +446,7 @@ int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
 	    !(prot & PROT_EXEC) || (vma->vm_flags & VM_EXEC))
 		return 0;
 
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	inode = file_inode(vma->vm_file);
 	action = ima_get_action(file_mnt_user_ns(vma->vm_file), inode,
 				current_cred(), secid, MAY_EXEC, MMAP_CHECK,
@@ -487,7 +487,7 @@ int ima_bprm_check(struct linux_binprm *bprm)
 	int ret;
 	u32 secid;
 
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	ret = process_measurement(bprm->file, current_cred(), secid, NULL, 0,
 				  MAY_EXEC, BPRM_CHECK);
 	if (ret)
@@ -512,7 +512,7 @@ int ima_file_check(struct file *file, int mask)
 {
 	u32 secid;
 
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	return process_measurement(file, current_cred(), secid, NULL, 0,
 				   mask & (MAY_READ | MAY_WRITE | MAY_EXEC |
 					   MAY_APPEND), FILE_CHECK);
@@ -709,7 +709,7 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id,
 
 	/* Read entire file for all partial reads. */
 	func = read_idmap[read_id] ?: FILE_CHECK;
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	return process_measurement(file, current_cred(), secid, NULL,
 				   0, MAY_READ, func);
 }
@@ -752,7 +752,7 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
 	}
 
 	func = read_idmap[read_id] ?: FILE_CHECK;
-	security_task_getsecid_subj(current, &secid);
+	security_current_getsecid_subj(&secid);
 	return process_measurement(file, current_cred(), secid, buf, size,
 				   MAY_READ, func);
 }
@@ -905,7 +905,7 @@ int process_buffer_measurement(struct user_namespace *mnt_userns,
 	 * buffer measurements.
 	 */
 	if (func) {
-		security_task_getsecid_subj(current, &secid);
+		security_current_getsecid_subj(&secid);
 		action = ima_get_action(mnt_userns, inode, current_cred(),
 					secid, 0, func, &pcr, &template,
 					func_data, NULL);

diff --git a/security/security.c b/security/security.c
@@ -1808,12 +1808,12 @@ int security_task_getsid(struct task_struct *p)
 	return call_int_hook(task_getsid, 0, p);
 }
 
-void security_task_getsecid_subj(struct task_struct *p, u32 *secid)
+void security_current_getsecid_subj(u32 *secid)
 {
 	*secid = 0;
-	call_void_hook(task_getsecid_subj, p, secid);
+	call_void_hook(current_getsecid_subj, secid);
 }
-EXPORT_SYMBOL(security_task_getsecid_subj);
+EXPORT_SYMBOL(security_current_getsecid_subj);
 
 void security_task_getsecid_obj(struct task_struct *p, u32 *secid)
 {

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
@@ -229,19 +229,6 @@ static inline u32 cred_sid(const struct cred *cred)
 	return tsec->sid;
 }
 
-/*
- * get the subjective security ID of a task
- */
-static inline u32 task_sid_subj(const struct task_struct *task)
-{
-	u32 sid;
-
-	rcu_read_lock();
-	sid = cred_sid(rcu_dereference(task->cred));
-	rcu_read_unlock();
-	return sid;
-}
-
 /*
  * get the objective security ID of a task
  */
@@ -4205,9 +4192,9 @@ static int selinux_task_getsid(struct task_struct *p)
 			    PROCESS__GETSESSION, NULL);
 }
 
-static void selinux_task_getsecid_subj(struct task_struct *p, u32 *secid)
+static void selinux_current_getsecid_subj(u32 *secid)
 {
-	*secid = task_sid_subj(p);
+	*secid = current_sid();
 }
 
 static void selinux_task_getsecid_obj(struct task_struct *p, u32 *secid)
@@ -7159,7 +7146,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(task_setpgid, selinux_task_setpgid),
 	LSM_HOOK_INIT(task_getpgid, selinux_task_getpgid),
 	LSM_HOOK_INIT(task_getsid, selinux_task_getsid),
-	LSM_HOOK_INIT(task_getsecid_subj, selinux_task_getsecid_subj),
+	LSM_HOOK_INIT(current_getsecid_subj, selinux_current_getsecid_subj),
 	LSM_HOOK_INIT(task_getsecid_obj, selinux_task_getsecid_obj),
 	LSM_HOOK_INIT(task_setnice, selinux_task_setnice),
 	LSM_HOOK_INIT(task_setioprio, selinux_task_setioprio),

diff --git a/security/smack/smack.h b/security/smack/smack.h
@@ -389,22 +389,6 @@ static inline struct smack_known *smk_of_task(const struct task_smack *tsp)
 	return tsp->smk_task;
 }
 
-static inline struct smack_known *smk_of_task_struct_subj(
-						const struct task_struct *t)
-{
-	struct smack_known *skp;
-	const struct cred *cred;
-
-	rcu_read_lock();
-
-	cred = rcu_dereference(t->cred);
-	skp = smk_of_task(smack_cred(cred));
-
-	rcu_read_unlock();
-
-	return skp;
-}
-
 static inline struct smack_known *smk_of_task_struct_obj(
 						const struct task_struct *t)
 {

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
@@ -2067,15 +2067,14 @@ static int smack_task_getsid(struct task_struct *p)
 }
 
 /**
- * smack_task_getsecid_subj - get the subjective secid of the task
- * @p: the task
+ * smack_current_getsecid_subj - get the subjective secid of the current task
  * @secid: where to put the result
  *
  * Sets the secid to contain a u32 version of the task's subjective smack label.
  */
-static void smack_task_getsecid_subj(struct task_struct *p, u32 *secid)
+static void smack_current_getsecid_subj(u32 *secid)
 {
-	struct smack_known *skp = smk_of_task_struct_subj(p);
+	struct smack_known *skp = smk_of_current();
 
 	*secid = skp->smk_secid;
 }
@@ -4807,7 +4806,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(task_setpgid, smack_task_setpgid),
 	LSM_HOOK_INIT(task_getpgid, smack_task_getpgid),
 	LSM_HOOK_INIT(task_getsid, smack_task_getsid),
-	LSM_HOOK_INIT(task_getsecid_subj, smack_task_getsecid_subj),
+	LSM_HOOK_INIT(current_getsecid_subj, smack_current_getsecid_subj),
 	LSM_HOOK_INIT(task_getsecid_obj, smack_task_getsecid_obj),
 	LSM_HOOK_INIT(task_setnice, smack_task_setnice),
 	LSM_HOOK_INIT(task_setioprio, smack_task_setioprio),