linux-kernel - [PATCHv2 2/2] audit: fix exe_file access in audit_exe

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Message-Id: <1471962039-14940-3-git-send-email-mguzik@redhat.com>
Date:   Tue, 23 Aug 2016 16:20:39 +0200
From:   Mateusz Guzik <mguzik@...hat.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Richard Guy Briggs <rgb@...hat.com>
Cc:     ebiederm@...ssion.com, oleg@...hat.com, sgrubb@...hat.com,
        pmoore@...hat.com, eparis@...hat.com, luto@...capital.net,
        linux-audit@...hat.com, linux-kernel@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCHv2 2/2] audit: fix exe_file access in audit_exe_compare

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

diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index d6709eb..0d302a8 100644
--- 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 *tsk, struct audit_fsnotify_mark *mark)
 	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);
 }
-- 
1.8.3.1