[RFC PATCH ghak90 (was ghak32) V3 01/10] 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_ID 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_ID 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 or re-set the audit container identifier.
A child inherits its parent's audit container identifier, but then can
be set only once after.

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>
---
 fs/proc/base.c             | 37 ++++++++++++++++++++++++
 include/linux/audit.h      | 25 ++++++++++++++++
 include/uapi/linux/audit.h |  2 ++
 kernel/auditsc.c           | 71 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 135 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index eafa39a..318dff4 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1302,6 +1302,41 @@ 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
@@ -2995,6 +3030,7 @@ static int proc_pid_patch_state(struct seq_file *m, struct pid_namespace *ns,
 #ifdef CONFIG_AUDITSYSCALL
 	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),
@@ -3386,6 +3422,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
 #ifdef CONFIG_AUDITSYSCALL
 	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 4f824c4..497cd81 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -219,6 +219,8 @@ static inline void audit_log_task_info(struct audit_buffer *ab,
 struct audit_task_info {
 	kuid_t			loginuid;
 	unsigned int		sessionid;
+	u64			contid;
+	bool			inherited; /* containerid inheritance */
 	struct audit_context	*ctx;
 };
 extern struct audit_task_info init_struct_audit;
@@ -331,6 +333,7 @@ static inline void audit_ptrace(struct task_struct *t)
 extern int auditsc_get_stamp(struct audit_context *ctx,
 			      struct timespec64 *t, unsigned int *serial);
 extern int audit_set_loginuid(kuid_t loginuid);
+extern int audit_set_contid(struct task_struct *tsk, u64 contid);
 
 static inline kuid_t audit_get_loginuid(struct task_struct *tsk)
 {
@@ -348,6 +351,14 @@ 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)
+{
+	if (!tsk->audit)
+		return AUDIT_CID_UNSET;
+	else
+		return tsk->audit->contid;
+}
+
 extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp);
 extern void __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode);
 extern void __audit_bprm(struct linux_binprm *bprm);
@@ -542,6 +553,10 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk)
 {
 	return AUDIT_SID_UNSET;
 }
+static inline kuid_t audit_get_contid(struct task_struct *tsk)
+{
+	return AUDIT_CID_UNSET;
+}
 static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
 { }
 static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid,
@@ -606,6 +621,16 @@ static inline bool audit_loginuid_set(struct task_struct *tsk)
 	return uid_valid(audit_get_loginuid(tsk));
 }
 
+static inline bool cid_valid(u64 contid)
+{
+	return contid != AUDIT_CID_UNSET;
+}
+
+static inline bool audit_contid_set(struct task_struct *tsk)
+{
+	return cid_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 04f9bd2..c3b1aca 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_ID	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 */
@@ -466,6 +467,7 @@ 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/auditsc.c b/kernel/auditsc.c
index 59ef7a81..611e926 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -956,6 +956,8 @@ int audit_alloc(struct task_struct *tsk)
 		return -ENOMEM;
 	info->loginuid = audit_get_loginuid(current);
 	info->sessionid = audit_get_sessionid(current);
+	info->contid = audit_get_contid(current);
+	info->inherited = true;
 	tsk->audit = info;
 
 	if (likely(!audit_ever_enabled))
@@ -985,6 +987,8 @@ 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,
+	.inherited = true,
 	.ctx = NULL,
 };
 
@@ -2112,6 +2116,73 @@ int audit_set_loginuid(kuid_t loginuid)
 }
 
 /**
+ * audit_set_contid - set current task's audit_context 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)];
+
+	/* Can't set if audit disabled */
+	if (!task->audit)
+		return -ENOPROTOOPT;
+	oldcontid = audit_get_contid(task);
+	/* Don't allow the audit containerid to be unset */
+	if (!cid_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;
+	/* it is already set, and not inherited from the parent, reject */
+	else if (cid_valid(oldcontid) && !task->audit->inherited)
+		rc = -EEXIST;
+	if (!rc) {
+		task_lock(task);
+		task->audit->contid = contid;
+		task->audit->inherited = false;
+		task_unlock(task);
+	}
+
+	if (!audit_enabled)
+		return rc;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_CONTAINER_ID);
+	if (!ab)
+		return rc;
+
+	uid = from_kuid(&init_user_ns, task_uid(current));
+	tty = audit_get_tty(current);
+	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_mq_open - record audit data for a POSIX MQ open
  * @oflag: open flag
  * @mode: mode bits
-- 
1.8.3.1