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>

4 files changed, 6 insertions, 29 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 41b8cb115801..8202e5583479 100644
--- a/security/apparmor/lsm.c
+++ b/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') {
diff --git a/security/security.c b/security/security.c
index f825304f04a7..32052f5c76b2 100644
--- a/security/security.c
+++ b/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)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 262e108c36d4..bada3cd42b9c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5862,8 +5862,7 @@ bad:
 	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.
 	 */
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 94dc9d406ce3..8da4a6b9ca4d 100644
--- a/security/smack/smack_lsm.c
+++ b/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;