proc,security: move restriction on writing /proc/pid/attr nodes to proc

Processes can only alter their own security attributes via
/proc/pid/attr nodes.  This is presently enforced by each individual
security module and is also imposed by the Linux credentials
implementation, which only allows a task to alter its own credentials.
Move the check enforcing this restriction from the individual
security modules to proc_pid_attr_write() before calling the security hook,
and drop the unnecessary task argument to the security hook since it can
only ever be the current task.
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

fs/proc/base.c

@@ -2488,6 +2488,12 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
 	length = -ESRCH;
 	if (!task)
 		goto out_no_task;
+
+	/* A task may only write its own attributes. */
+	length = -EACCES;
+	if (current != task)
+		goto out;
+
 	if (count > PAGE_SIZE)
 		count = PAGE_SIZE;
 
@@ -2503,14 +2509,13 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
 	}
 
 	/* Guard against adverse ptrace interaction */
-	length = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
+	length = mutex_lock_interruptible(&current->signal->cred_guard_mutex);
 	if (length < 0)
 		goto out_free;
 
-	length = security_setprocattr(task,
-				      (char*)file->f_path.dentry->d_name.name,
+	length = security_setprocattr(file->f_path.dentry->d_name.name,
 				      page, count);
-	mutex_unlock(&task->signal->cred_guard_mutex);
+	mutex_unlock(&current->signal->cred_guard_mutex);
 out_free:
 	kfree(page);
 out:

include/linux/lsm_hooks.h

@@ -1547,8 +1547,7 @@ union security_list_options {
 	void (*d_instantiate)(struct dentry *dentry, struct inode *inode);
 
 	int (*getprocattr)(struct task_struct *p, char *name, char **value);
-	int (*setprocattr)(struct task_struct *p, char *name, void *value,
-				size_t size);
+	int (*setprocattr)(const char *name, void *value, size_t size);
 	int (*ismaclabel)(const char *name);
 	int (*secid_to_secctx)(u32 secid, char **secdata, u32 *seclen);
 	int (*secctx_to_secid)(const char *secdata, u32 seclen, u32 *secid);

include/linux/security.h

@@ -361,7 +361,7 @@ int security_sem_semop(struct sem_array *sma, struct sembuf *sops,
 			unsigned nsops, int alter);
 void security_d_instantiate(struct dentry *dentry, struct inode *inode);
 int security_getprocattr(struct task_struct *p, char *name, char **value);
-int security_setprocattr(struct task_struct *p, char *name, void *value, size_t size);
+int security_setprocattr(const char *name, void *value, size_t size);
 int security_netlink_send(struct sock *sk, struct sk_buff *skb);
 int security_ismaclabel(const char *name);
 int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen);
@@ -1106,7 +1106,7 @@ static inline int security_getprocattr(struct task_struct *p, char *name, char *
 	return -EINVAL;
 }
 
-static inline int security_setprocattr(struct task_struct *p, char *name, void *value, size_t size)
+static inline int security_setprocattr(char *name, void *value, size_t size)
 {
 	return -EINVAL;
 }

security/apparmor/lsm.c

@@ -495,8 +495,8 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 	return error;
 }
 
-static int apparmor_setprocattr(struct task_struct *task, char *name,
-				void *value, size_t size)
+static int apparmor_setprocattr(const char *name, void *value,
+				size_t size)
 {
 	struct common_audit_data sa;
 	struct apparmor_audit_data aad = {0,};
@@ -506,9 +506,6 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 
 	if (size == 0)
 		return -EINVAL;
-	/* task can only write its own attributes */
-	if (current != task)
-		return -EACCES;
 
 	/* AppArmor requires that the buffer must be null terminated atm */
 	if (args[size - 1] != '\0') {

security/security.c

@@ -1170,9 +1170,9 @@ int security_getprocattr(struct task_struct *p, char *name, char **value)
 	return call_int_hook(getprocattr, -EINVAL, p, name, value);
 }
 
-int security_setprocattr(struct task_struct *p, char *name, void *value, size_t size)
+int security_setprocattr(const char *name, void *value, size_t size)
 {
-	return call_int_hook(setprocattr, -EINVAL, p, name, value, size);
+	return call_int_hook(setprocattr, -EINVAL, name, value, size);
 }
 
 int security_netlink_send(struct sock *sk, struct sk_buff *skb)

security/selinux/hooks.c

@@ -5862,8 +5862,7 @@ static int selinux_getprocattr(struct task_struct *p,
 	return error;
 }
 
-static int selinux_setprocattr(struct task_struct *p,
-			       char *name, void *value, size_t size)
+static int selinux_setprocattr(const char *name, void *value, size_t size)
 {
 	struct task_security_struct *tsec;
 	struct cred *new;
@@ -5871,16 +5870,6 @@ static int selinux_setprocattr(struct task_struct *p,
 	int error;
 	char *str = value;
 
-	if (current != p) {
-		/*
-		 * A task may only alter its own credentials.
-		 * SELinux has always enforced this restriction,
-		 * and it is now mandated by the Linux credentials
-		 * infrastructure; see Documentation/security/credentials.txt.
-		 */
-		return -EACCES;
-	}
-
 	/*
 	 * Basic control over ability to set these attributes at all.
 	 */

security/smack/smack_lsm.c

@@ -3620,7 +3620,6 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 
 /**
  * smack_setprocattr - Smack process attribute setting
- * @p: the object task
  * @name: the name of the attribute in /proc/.../attr
  * @value: the value to set
  * @size: the size of the value
@@ -3630,8 +3629,7 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
  *
  * Returns the length of the smack label or an error code
  */
-static int smack_setprocattr(struct task_struct *p, char *name,
-			     void *value, size_t size)
+static int smack_setprocattr(const char *name, void *value, size_t size)
 {
 	struct task_smack *tsp = current_security();
 	struct cred *new;
@@ -3639,13 +3637,6 @@ static int smack_setprocattr(struct task_struct *p, char *name,
 	struct smack_known_list_elem *sklep;
 	int rc;
 
-	/*
-	 * Changing another process' Smack value is too dangerous
-	 * and supports no sane use case.
-	 */
-	if (p != current)
-		return -EPERM;
-
 	if (!smack_privileged(CAP_MAC_ADMIN) && list_empty(&tsp->smk_relabel))
 		return -EPERM;