[PATCH v2 2/3] kernel/audit: reduce mmap_sem hold for mm->exe_file

Davidlohr Bueso
2015-02-23T02:20:24Z

The mm->exe_file is currently serialized with mmap_sem (shared)
in order to both safely (1) read the file and (2) audit it via
audit_log_d_path(). Good users will, on the other hand, make use
of the more standard get_mm_exe_file(), requiring only holding
the mmap_sem to read the value, and relying on reference counting
to make sure that the exe file won't dissapear underneath us.

Additionally, upon NULL return of get_mm_exe_file, we also call
audit_log_format(ab, " exe=(null)").

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---

changes from v1: rebased on top of 1/1.

kernel/audit.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index a71cbfe..b446d54 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -43,6 +43,7 @@

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/file.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/atomic.h>
@@ -1841,15 +1842,20 @@ EXPORT_SYMBOL(audit_log_task_context);
void audit_log_d_path_exe(struct audit_buffer *ab,
struct mm_struct *mm)
{
- if (!mm) {
- audit_log_format(ab, " exe=(null)");
- return;
- }
+ struct file *exe_file;
+
+ if (!mm)
+ goto out_null;

- down_read(&mm->mmap_sem);
- if (mm->exe_file)
- audit_log_d_path(ab, " exe=", &mm->exe_file->f_path);
- up_read(&mm->mmap_sem);
+ exe_file = get_mm_exe_file(mm);
+ if (!exe_file)
+ goto out_null;
+
+ audit_log_d_path(ab, " exe=", &exe_file->f_path);
+ fput(exe_file);
+ return;
+out_null:
+ audit_log_format(ab, " exe=(null)");
}

void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk)
--
2.1.4