linux-kernel - [PATCH 4.4 020/118] audit: fix exe_file access in audit_exe

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Message-Id: <20160922172939.630065749@linuxfoundation.org>
Date:   Thu, 22 Sep 2016 19:28:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mateusz Guzik <mguzik@...hat.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Richard Guy Briggs <rgb@...hat.com>,
        Paul Moore <paul@...l-moore.com>
Subject: [PATCH 4.4 020/118] audit: fix exe_file access in audit_exe_compare

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mateusz Guzik <mguzik@...hat.com>

commit 5efc244346f9f338765da3d592f7947b0afdc4b5 upstream.

Prior to the change the function would blindly deference mm, exe_file
and exe_file->f_inode, each of which could have been NULL or freed.

Use get_task_exe_file to safely obtain stable exe_file.

Signed-off-by: Mateusz Guzik <mguzik@...hat.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Acked-by: Richard Guy Briggs <rgb@...hat.com>
Signed-off-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/audit_watch.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -19,6 +19,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
+#include <linux/file.h>
 #include <linux/kernel.h>
 #include <linux/audit.h>
 #include <linux/kthread.h>
@@ -544,10 +545,11 @@ int audit_exe_compare(struct task_struct
 	unsigned long ino;
 	dev_t dev;
 
-	rcu_read_lock();
-	exe_file = rcu_dereference(tsk->mm->exe_file);
+	exe_file = get_task_exe_file(tsk);
+	if (!exe_file)
+		return 0;
 	ino = exe_file->f_inode->i_ino;
 	dev = exe_file->f_inode->i_sb->s_dev;
-	rcu_read_unlock();
+	fput(exe_file);
 	return audit_mark_compare(mark, ino, dev);
 }