[PATCH ghak90 V5 02/10] 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 old-contid=18446744073709551615 contid=123456 pid=628 auid=root uid=root tty=ttyS0 ses=1 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 comm=bash exe=/usr/bin/bash res=yes

The "op" field indicates an initial set.  The "pid" to "ses" fields are
the orchestrator while the "opid" field is the object's PID, the process
being "contained".  Old and new audit container identifier values are
given in the "contid" fields, while res indicates its success.

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

See: https://github.com/linux-audit/audit-kernel/issues/90
See: https://github.com/linux-audit/audit-userspace/issues/51
See: https://github.com/linux-audit/audit-testsuite/issues/64
See: 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>
Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
---
 fs/proc/base.c             | 36 ++++++++++++++++++++++++
 include/linux/audit.h      | 25 +++++++++++++++++
 include/uapi/linux/audit.h |  2 ++
 kernel/audit.c             | 68 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 131 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a23651ce6960..2505c46c8701 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1294,6 +1294,40 @@ 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
@@ -3005,6 +3039,7 @@ 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),
@@ -3393,6 +3428,7 @@ 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 bde346e73f0c..301337776193 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -89,6 +89,7 @@ struct audit_field {
 struct audit_task_info {
 	kuid_t			loginuid;
 	unsigned int		sessionid;
+	u64			contid;
 #ifdef CONFIG_AUDITSYSCALL
 	struct audit_context	*ctx;
 #endif
@@ -189,6 +190,15 @@ 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)
+		return AUDIT_CID_UNSET;
+	return tsk->audit->contid;
+}
+
 extern u32 audit_enabled;
 #else /* CONFIG_AUDIT */
 static inline int audit_alloc(struct task_struct *task)
@@ -250,6 +260,11 @@ 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
 #endif /* CONFIG_AUDIT */
 
@@ -606,6 +621,16 @@ 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 36a7e3f18e69..d475cf3b4d7f 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 information */
 
 #define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
 #define AUDIT_USER_AVC		1107	/* We filter this differently */
@@ -471,6 +472,7 @@ 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 67498c5690bb..b5c702abeb42 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -244,6 +244,7 @@ int audit_alloc(struct task_struct *tsk)
 	}
 	info->loginuid = audit_get_loginuid(current);
 	info->sessionid = audit_get_sessionid(current);
+	info->contid = audit_get_contid(current);
 	tsk->audit = info;
 
 	ret = audit_alloc_syscall(tsk);
@@ -258,6 +259,7 @@ int audit_alloc(struct task_struct *tsk)
 struct audit_task_info init_struct_audit = {
 	.loginuid = INVALID_UID,
 	.sessionid = AUDIT_SID_UNSET,
+	.contid = AUDIT_CID_UNSET,
 #ifdef CONFIG_AUDITSYSCALL
 	.ctx = NULL,
 #endif
@@ -2341,6 +2343,72 @@ int audit_set_loginuid(kuid_t loginuid)
 }
 
 /**
+ * audit_set_contid - set current task's audit contid
+ * @contid: contid value
+ *
+ * Returns 0 on success, -EPERM on permission failure.
+ *
+ * Called (set) from fs/proc/base.c::proc_contid_write().
+ */
+int audit_set_contid(struct task_struct *task, u64 contid)
+{
+	u64 oldcontid;
+	int rc = 0;
+	struct audit_buffer *ab;
+	uid_t uid;
+	struct tty_struct *tty;
+	char comm[sizeof(current->comm)];
+
+	task_lock(task);
+	/* Can't set if audit disabled */
+	if (!task->audit) {
+		task_unlock(task);
+		return -ENOPROTOOPT;
+	}
+	oldcontid = audit_get_contid(task);
+	read_lock(&tasklist_lock);
+	/* Don't allow the audit containerid to be unset */
+	if (!audit_contid_valid(contid))
+		rc = -EINVAL;
+	/* if we don't have caps, reject */
+	else if (!capable(CAP_AUDIT_CONTROL))
+		rc = -EPERM;
+	/* if task has children or is not single-threaded, deny */
+	else if (!list_empty(&task->children))
+		rc = -EBUSY;
+	else if (!(thread_group_leader(task) && thread_group_empty(task)))
+		rc = -EALREADY;
+	read_unlock(&tasklist_lock);
+	if (!rc)
+		task->audit->contid = contid;
+	task_unlock(task);
+
+	if (!audit_enabled)
+		return rc;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONTAINER_OP);
+	if (!ab)
+		return rc;
+
+	uid = from_kuid(&init_user_ns, task_uid(current));
+	tty = audit_get_tty();
+	audit_log_format(ab, "op=set opid=%d old-contid=%llu contid=%llu pid=%d uid=%u auid=%u tty=%s ses=%u",
+			 task_tgid_nr(task), oldcontid, contid,
+			 task_tgid_nr(current), uid,
+			 from_kuid(&init_user_ns, audit_get_loginuid(current)),
+			 tty ? tty_name(tty) : "(none)",
+			 audit_get_sessionid(current));
+	audit_put_tty(tty);
+	audit_log_task_context(ab);
+	audit_log_format(ab, " comm=");
+	audit_log_untrustedstring(ab, get_task_comm(comm, current));
+	audit_log_d_path_exe(ab, current->mm);
+	audit_log_format(ab, " res=%d", !rc);
+	audit_log_end(ab);
+	return rc;
+}
+
+/**
  * audit_log_end - end one audit record
  * @ab: the audit_buffer
  *
-- 
1.8.3.1