[PATCH ghak90 V9 02/13] audit: add container id

[Richard Guy Briggs]

Implement the proc fs write to set the audit container identifier of a
process, emitting an AUDIT_CONTAINER_OP record to document the event.

This is a write from the container orchestrator task to a proc entry of
the form /proc/PID/audit_containerid where PID is the process ID of the
newly created task that is to become the first task in a container, or
an additional task added to a container.

The write expects up to a u64 value (unset: 18446744073709551615).

The writer must have capability CAP_AUDIT_CONTROL.

This will produce a record such as this:
  type=CONTAINER_OP msg=audit(2018-06-06 12:39:29.636:26949) : op=set opid=2209 contid=123456 old-contid=18446744073709551615

The "op" field indicates an initial set.  The "opid" field is the
object's PID, the process being "contained".  New and old audit
container identifier values are given in the "contid" fields.

It is not permitted to unset the audit container identifier.
A child inherits its parent's audit container identifier.

Store the audit container identifier in a refcounted kernel object that
is added to the master list of audit container identifiers.  This will
allow multiple container orchestrators/engines to work on the same
machine without danger of inadvertantly re-using an existing identifier.
It will also allow an orchestrator to inject a process into an existing
container by checking if the original container owner is the one
injecting the task.  A hash table list is used to optimize searches.

Please see the github audit kernel issue for the main feature:
  https://github.com/linux-audit/audit-kernel/issues/90
Please see the github audit userspace issue for supporting additions:
  https://github.com/linux-audit/audit-userspace/issues/51
Please see the github audit testsuiite issue for the test case:
  https://github.com/linux-audit/audit-testsuite/issues/64
Please see the github audit wiki for the feature overview:
  https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID

Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
Acked-by: Serge Hallyn <serge@xxxxxxxxxx>
Acked-by: Steve Grubb <sgrubb@xxxxxxxxxx>
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Reviewed-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
 fs/proc/base.c             |  36 +++++++++++
 include/linux/audit.h      |  33 ++++++++++
 include/uapi/linux/audit.h |   2 +
 kernel/audit.c             | 148 +++++++++++++++++++++++++++++++++++++++++++++
 kernel/audit.h             |   8 +++
 5 files changed, 227 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index d86c0afc8a85..6c17ab32e71b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1317,6 +1317,40 @@ static ssize_t proc_sessionid_read(struct file * file, char __user * buf,
 	.read		= proc_sessionid_read,
 	.llseek		= generic_file_llseek,
 };
+
+static ssize_t proc_contid_write(struct file *file, const char __user *buf,
+				   size_t count, loff_t *ppos)
+{
+	struct inode *inode = file_inode(file);
+	u64 contid;
+	int rv;
+	struct task_struct *task = get_proc_task(inode);
+
+	if (!task)
+		return -ESRCH;
+	if (*ppos != 0) {
+		/* No partial writes. */
+		put_task_struct(task);
+		return -EINVAL;
+	}
+
+	rv = kstrtou64_from_user(buf, count, 10, &contid);
+	if (rv < 0) {
+		put_task_struct(task);
+		return rv;
+	}
+
+	rv = audit_set_contid(task, contid);
+	put_task_struct(task);
+	if (rv < 0)
+		return rv;
+	return count;
+}
+
+static const struct file_operations proc_contid_operations = {
+	.write		= proc_contid_write,
+	.llseek		= generic_file_llseek,
+};
 #endif
 
 #ifdef CONFIG_FAULT_INJECTION
@@ -3219,6 +3253,7 @@ static int proc_stack_depth(struct seq_file *m, struct pid_namespace *ns,
 #ifdef CONFIG_AUDIT
 	REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
+	REG("audit_containerid", S_IWUSR, proc_contid_operations),
 #endif
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
@@ -3558,6 +3593,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
 #ifdef CONFIG_AUDIT
 	REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
+	REG("audit_containerid", S_IWUSR, proc_contid_operations),
 #endif
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
diff --git a/include/linux/audit.h b/include/linux/audit.h
index c2150415f9df..2800d4f1a2a8 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -100,9 +100,18 @@ enum audit_nfcfgop {
 	AUDIT_XT_OP_UNREGISTER,
 };
 
+struct audit_contobj {
+	struct list_head	list;
+	u64			id;
+	struct task_struct	*owner;
+	refcount_t		refcount;
+	struct rcu_head         rcu;
+};
+
 struct audit_task_info {
 	kuid_t			loginuid;
 	unsigned int		sessionid;
+	struct audit_contobj	*cont;
 #ifdef CONFIG_AUDITSYSCALL
 	struct audit_context	*ctx;
 #endif
@@ -204,6 +213,15 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
 	return tsk->audit->sessionid;
 }
 
+extern int audit_set_contid(struct task_struct *tsk, u64 contid);
+
+static inline u64 audit_get_contid(struct task_struct *tsk)
+{
+	if (!tsk->audit || !tsk->audit->cont)
+		return AUDIT_CID_UNSET;
+	return tsk->audit->cont->id;
+}
+
 extern u32 audit_enabled;
 
 extern int audit_signal_info(int sig, struct task_struct *t);
@@ -268,6 +286,11 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
 	return AUDIT_SID_UNSET;
 }
 
+static inline u64 audit_get_contid(struct task_struct *tsk)
+{
+	return AUDIT_CID_UNSET;
+}
+
 #define audit_enabled AUDIT_OFF
 
 static inline int audit_signal_info(int sig, struct task_struct *t)
@@ -692,6 +715,16 @@ static inline bool audit_loginuid_set(struct task_struct *tsk)
 	return uid_valid(audit_get_loginuid(tsk));
 }
 
+static inline bool audit_contid_valid(u64 contid)
+{
+	return contid != AUDIT_CID_UNSET;
+}
+
+static inline bool audit_contid_set(struct task_struct *tsk)
+{
+	return audit_contid_valid(audit_get_contid(tsk));
+}
+
 static inline void audit_log_string(struct audit_buffer *ab, const char *buf)
 {
 	audit_log_n_string(ab, buf, strlen(buf));
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 9b6a973f4cc3..859382527210 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -71,6 +71,7 @@
 #define AUDIT_TTY_SET		1017	/* Set TTY auditing status */
 #define AUDIT_SET_FEATURE	1018	/* Turn an audit feature on or off */
 #define AUDIT_GET_FEATURE	1019	/* Get which features are enabled */
+#define AUDIT_CONTAINER_OP	1020	/* Define the container id and info */
 
 #define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
 #define AUDIT_USER_AVC		1107	/* We filter this differently */
@@ -491,6 +492,7 @@ struct audit_tty_status {
 
 #define AUDIT_UID_UNSET (unsigned int)-1
 #define AUDIT_SID_UNSET ((unsigned int)-1)
+#define AUDIT_CID_UNSET ((u64)-1)
 
 /* audit_rule_data supports filter rules with both integer and string
  * fields.  It corresponds with AUDIT_ADD_RULE, AUDIT_DEL_RULE and
diff --git a/kernel/audit.c b/kernel/audit.c
index 5d8147a29291..6d387793f702 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -138,6 +138,13 @@ struct auditd_connection {
 
 /* Hash for inode-based rules */
 struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];
+/* Hash for contid object lists */
+struct list_head audit_contid_hash[AUDIT_CONTID_BUCKETS];
+/* Lock all additions and deletions to the contid hash lists, assignment
+ * of container objects to tasks.  There should be no need for
+ * interaction with tasklist_lock
+ */
+static DEFINE_SPINLOCK(audit_contobj_list_lock);
 
 static struct kmem_cache *audit_buffer_cache;
 
@@ -212,6 +219,33 @@ void __init audit_task_init(void)
 					     0, SLAB_PANIC, NULL);
 }
 
+/* rcu_read_lock must be held by caller unless new */
+static struct audit_contobj *_audit_contobj_hold(struct audit_contobj *cont)
+{
+	if (cont)
+		refcount_inc(&cont->refcount);
+	return cont;
+}
+
+static struct audit_contobj *_audit_contobj_get(struct task_struct *tsk)
+{
+	if (!tsk->audit)
+		return NULL;
+	return _audit_contobj_hold(tsk->audit->cont);
+}
+
+/* rcu_read_lock must be held by caller */
+static void _audit_contobj_put(struct audit_contobj *cont)
+{
+	if (!cont)
+		return;
+	if (refcount_dec_and_test(&cont->refcount)) {
+		put_task_struct(cont->owner);
+		list_del_rcu(&cont->list);
+		kfree_rcu(cont, rcu);
+	}
+}
+
 /**
  * audit_alloc - allocate an audit info block for a task
  * @tsk: task
@@ -232,6 +266,9 @@ int audit_alloc(struct task_struct *tsk)
 	}
 	info->loginuid = audit_get_loginuid(current);
 	info->sessionid = audit_get_sessionid(current);
+	rcu_read_lock();
+	info->cont = _audit_contobj_get(current);
+	rcu_read_unlock();
 	tsk->audit = info;
 
 	ret = audit_alloc_syscall(tsk);
@@ -246,6 +283,7 @@ int audit_alloc(struct task_struct *tsk)
 struct audit_task_info init_struct_audit = {
 	.loginuid = INVALID_UID,
 	.sessionid = AUDIT_SID_UNSET,
+	.cont = NULL,
 #ifdef CONFIG_AUDITSYSCALL
 	.ctx = NULL,
 #endif
@@ -262,6 +300,9 @@ void audit_free(struct task_struct *tsk)
 	struct audit_task_info *info = tsk->audit;
 
 	audit_free_syscall(tsk);
+	rcu_read_lock();
+	_audit_contobj_put(tsk->audit->cont);
+	rcu_read_unlock();
 	/* Freeing the audit_task_info struct must be performed after
 	 * audit_log_exit() due to need for loginuid and sessionid.
 	 */
@@ -1709,6 +1750,9 @@ static int __init audit_init(void)
 	for (i = 0; i < AUDIT_INODE_BUCKETS; i++)
 		INIT_LIST_HEAD(&audit_inode_hash[i]);
 
+	for (i = 0; i < AUDIT_CONTID_BUCKETS; i++)
+		INIT_LIST_HEAD(&audit_contid_hash[i]);
+
 	mutex_init(&audit_cmd_mutex.lock);
 	audit_cmd_mutex.owner = NULL;
 
@@ -2410,6 +2454,110 @@ int audit_signal_info(int sig, struct task_struct *t)
 	return audit_signal_info_syscall(t);
 }
 
+/*
+ * audit_set_contid - set current task's audit contid
+ * @task: target task
+ * @contid: contid value
+ *
+ * Returns 0 on success, -EPERM on permission failure.
+ *
+ * If the original container owner goes away, no task injection is
+ * possible to an existing container.
+ *
+ * Called (set) from fs/proc/base.c::proc_contid_write().
+ */
+int audit_set_contid(struct task_struct *task, u64 contid)
+{
+	int rc = 0;
+	struct audit_buffer *ab;
+	struct audit_contobj *oldcont = NULL;
+
+	task_lock(task);
+	/* Can't set if audit disabled */
+	if (!task->audit) {
+		task_unlock(task);
+		return -ENOPROTOOPT;
+	}
+	read_lock(&tasklist_lock);
+	/* Don't allow the contid to be unset */
+	if (!audit_contid_valid(contid)) {
+		rc = -EINVAL;
+		goto unlock;
+	}
+	/* if we don't have caps, reject */
+	if (!capable(CAP_AUDIT_CONTROL)) {
+		rc = -EPERM;
+		goto unlock;
+	}
+	/* if task has children or is not single-threaded, deny */
+	if (!list_empty(&task->children) ||
+	    !(thread_group_leader(task) && thread_group_empty(task))) {
+		rc = -EBUSY;
+		goto unlock;
+	}
+	/* if contid is already set, deny */
+	if (audit_contid_set(task))
+		rc = -EEXIST;
+unlock:
+	read_unlock(&tasklist_lock);
+	rcu_read_lock();
+	oldcont = _audit_contobj_get(task);
+	if (!rc) {
+		struct audit_contobj *cont = NULL, *newcont = NULL;
+		int h = audit_hash_contid(contid);
+
+		spin_lock(&audit_contobj_list_lock);
+		list_for_each_entry_rcu(cont, &audit_contid_hash[h], list)
+			if (cont->id == contid) {
+				/* task injection to existing container */
+				if (current == cont->owner) {
+					_audit_contobj_hold(cont);
+					newcont = cont;
+				} else {
+					rc = -ENOTUNIQ;
+					spin_unlock(&audit_contobj_list_lock);
+					goto conterror;
+				}
+				break;
+			}
+		if (!newcont) {
+			newcont = kmalloc(sizeof(*newcont), GFP_ATOMIC);
+			if (newcont) {
+				INIT_LIST_HEAD(&newcont->list);
+				newcont->id = contid;
+				newcont->owner = get_task_struct(current);
+				refcount_set(&newcont->refcount, 1);
+				list_add_rcu(&newcont->list,
+					     &audit_contid_hash[h]);
+			} else {
+				rc = -ENOMEM;
+				spin_unlock(&audit_contobj_list_lock);
+				goto conterror;
+			}
+		}
+		spin_unlock(&audit_contobj_list_lock);
+		task->audit->cont = newcont;
+		_audit_contobj_put(oldcont);
+	}
+conterror:
+	task_unlock(task);
+
+	if (!audit_enabled)
+		return rc;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONTAINER_OP);
+	if (!ab)
+		return rc;
+
+	audit_log_format(ab,
+			 "op=set opid=%d contid=%llu old-contid=%llu",
+			 task_tgid_nr(task), contid, oldcont ? oldcont->id : -1);
+	_audit_contobj_put(oldcont);
+	rcu_read_unlock();
+	audit_log_end(ab);
+	return rc;
+}
+
 /**
  * audit_log_end - end one audit record
  * @ab: the audit_buffer
diff --git a/kernel/audit.h b/kernel/audit.h
index 9bee09757068..182fc76ea276 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -210,6 +210,14 @@ static inline int audit_hash_ino(u32 ino)
 	return (ino & (AUDIT_INODE_BUCKETS-1));
 }
 
+#define AUDIT_CONTID_BUCKETS	32
+extern struct list_head audit_contid_hash[AUDIT_CONTID_BUCKETS];
+
+static inline int audit_hash_contid(u64 contid)
+{
+	return (contid & (AUDIT_CONTID_BUCKETS-1));
+}
+
 /* Indicates that audit should log the full pathname. */
 #define AUDIT_NAME_FULL -1
 
-- 
1.8.3.1