[PATCH 3/3] audit: Audit proc cmdline value

[William Roberts <bill.c.roberts@gmail.com>]

During an audit event, cache and print the value of the process's
cmdline value (proc/<pid>/cmdline). This is useful in situations
where processes are started via fork'd virtual machines where the
comm field is incorrect. Often times, setting the comm field still
is insufficient as the comm width is not very wide and most
virtual machine "package names" do not fit. Also, during execution,
many threads have thier comm field set as well. By tying it back to
the global cmdline value for the process, audit records will be more
complete in systems with these properties. An example of where this
is useful and applicable is in the realm of Android.

The cached cmdline is tied to the lifecycle of the audit_context
structure and is built on demand.

Signed-off-by: William Roberts <wroberts@tresys.com>
---
 kernel/audit.h   |    1 +
 kernel/auditsc.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/kernel/audit.h b/kernel/audit.h
index b779642..bd6211f 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -202,6 +202,7 @@ struct audit_context {
 		} execve;
 	};
 	int fds[2];
+	char *cmdline;
 
 #if AUDIT_DEBUG
 	int		    put_count;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 90594c9..bfb1698 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -842,6 +842,14 @@ static inline struct audit_context *audit_get_context(struct task_struct *tsk,
 	return context;
 }
 
+static inline void audit_cmdline_free(struct audit_context *context)
+{
+	if (!context->cmdline)
+		return;
+	kfree(context->cmdline);
+	context->cmdline = NULL;
+}
+
 static inline void audit_free_names(struct audit_context *context)
 {
 	struct audit_names *n, *next;
@@ -955,6 +963,7 @@ static inline void audit_free_context(struct audit_context *context)
 	audit_free_aux(context);
 	kfree(context->filterkey);
 	kfree(context->sockaddr);
+	audit_cmdline_free(context);
 	kfree(context);
 }
 
@@ -1271,6 +1280,78 @@ static void show_special(struct audit_context *context, int *call_panic)
 	audit_log_end(ab);
 }
 
+static char *audit_cmdline_get(struct audit_buffer *ab,
+			       struct task_struct *task)
+{
+	int len;
+	int res;
+	char *buf;
+	struct mm_struct *mm;
+
+	if (!ab || !task)
+		return NULL;
+
+	mm = get_task_mm(task);
+	if (!mm)
+		return NULL;
+
+	len = get_cmdline_length(mm);
+	if (!len)
+		goto mm_err;
+
+	if (len > PATH_MAX)
+		len = PATH_MAX;
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		goto mm_err;
+
+	res = copy_cmdline(task, mm, buf, len);
+	if (res <= 0)
+		goto alloc_err;
+
+	mmput(mm);
+	/*
+	 * res is guarenteed not to be longer than
+	 * than the buf as it was truncated to len
+	 * in copy_cmdline()
+	 */
+	len = res;
+
+	/*
+	 * Ensure NULL terminated as application
+	 * could be using setproctitle(3)
+	 */
+	buf[len-1] = '\0';
+	return buf;
+
+alloc_err:
+	kfree(buf);
+mm_err:
+	mmput(mm);
+	return NULL;
+}
+
+static void audit_log_cmdline(struct audit_buffer *ab, struct task_struct *tsk,
+			 struct audit_context *context)
+{
+	char *msg = "(null)";
+	audit_log_format(ab, " cmdline=");
+
+	/* Already cached */
+	if (context->cmdline) {
+		msg = context->cmdline;
+		goto out;
+	}
+	/* Not cached */
+	context->cmdline = audit_cmdline_get(ab, tsk);
+	if (!context->cmdline)
+		goto out;
+	msg = context->cmdline;
+out:
+	audit_log_untrustedstring(ab, msg);
+}
+
 static void audit_log_exit(struct audit_context *context, struct task_struct *tsk)
 {
 	int i, call_panic = 0;
@@ -1302,6 +1383,7 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 			 context->name_count);
 
 	audit_log_task_info(ab, tsk);
+	audit_log_cmdline(ab, tsk, context);
 	audit_log_key(ab, context->filterkey);
 	audit_log_end(ab);
 
-- 
1.7.9.5

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