[PATCH 2/4] audit: Enable cacheing of cmdline in audit_context

[William Roberts]

Rather then reading from userspace on every call,
cache the page in the audit_context and couple
to that objects life-cycle.

Change-Id: Ia0d432bc4aba8588840f0dc0026a1e9483e5b485
Signed-off-by: William Roberts <wroberts at tresys.com>
---
 kernel/auditsc.c |   48 +++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 11 deletions(-)

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 45fd3d0..27f8224 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -270,6 +270,7 @@ struct audit_context {
 		} mmap;
 	};
 	int fds[2];
+	char *cmdline;
 
 #if AUDIT_DEBUG
 	int		    put_count;
@@ -1044,6 +1045,14 @@ static inline void audit_free_aux(struct audit_context *context)
 	}
 }
 
+static inline void audit_cmdline_free(struct audit_context *ctx)
+{
+	if (!ctx->cmdline)
+		return;
+	free_page((unsigned long)ctx->cmdline);
+	ctx->cmdline = NULL;
+}
+
 static inline void audit_zero_context(struct audit_context *context,
 				      enum audit_state state)
 {
@@ -1118,6 +1127,7 @@ 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);
 		context  = previous;
 	} while (context);
@@ -1154,35 +1164,51 @@ error_path:
 
 EXPORT_SYMBOL(audit_log_task_context);
 
-static void audit_log_add_cmdline(struct audit_buffer *ab,
+static char *audit_cmdline_get_page(struct audit_buffer *ab,
 				  struct task_struct *tsk)
 {
 	int len;
 	unsigned long page;
-	char *msg = "(null)";
-
-	audit_log_format(ab, " cmdline=");
 
 	/* Get the process cmdline */
 	page = __get_free_page(GFP_TEMPORARY);
 	if (!page) {
-		audit_log_untrustedstring(ab, msg);
-		return;
+		return NULL;
 	}
 	len = proc_pid_cmdline(tsk, (char *)page);
 	if (len <= 0) {
 		free_page(page);
-		audit_log_untrustedstring(ab, msg);
-		return;
+		return NULL;
 	}
 	/*
 	 * Ensure NULL terminated! Application could
 	 * could be using setproctitle(3).
 	 */
 	((char *)page)[len-1] = '\0';
-	msg = (char *)page;
+
+	/* XXX: Re-alloc to something smaller then a page here? */
+	return (char *)page;
+}
+
+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 yet */
+	context->cmdline = audit_cmdline_get_page(ab, tsk);
+	if (!context->cmdline)
+		goto out;
+	msg = context->cmdline;
+out:
 	audit_log_untrustedstring(ab, msg);
-	free_page(page);
 }
 
 static void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
@@ -1211,7 +1237,6 @@ static void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk
 		}
 		up_read(&mm->mmap_sem);
 	}
-	audit_log_add_cmdline(ab, tsk);
 	audit_log_task_context(ab);
 }
 
@@ -1679,6 +1704,7 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 
 
 	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