* [PATCH] audit: fix audit_exe_compare using get_mm_exe_file
@ 2016-08-22 15:41 Richard Guy Briggs
2016-08-22 16:27 ` Mateusz Guzik
0 siblings, 1 reply; 2+ messages in thread
From: Richard Guy Briggs @ 2016-08-22 15:41 UTC (permalink / raw)
To: linux-audit, linux-kernel
Cc: Richard Guy Briggs, mguzik, ebiederm, oleg, skinsbursky, luto,
sgrubb, pmoore, eparis
Fix original naive attempt to get/lock access to task->mm->exe_file by
using get_mm_exe_file and checking for NULL.
See: https://lkml.org/lkml/2016/7/30/97
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
kernel/audit_watch.c | 13 ++++++++++---
1 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index d6709eb..0b29279 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>
@@ -540,14 +541,20 @@ int audit_dupe_exe(struct audit_krule *new, struct audit_krule *old)
int audit_exe_compare(struct task_struct *tsk, struct audit_fsnotify_mark *mark)
{
+ struct mm_struct *mm;
struct file *exe_file;
unsigned long ino;
dev_t dev;
- rcu_read_lock();
- exe_file = rcu_dereference(tsk->mm->exe_file);
+ mm = get_task_mm(tsk);
+ if (!mm)
+ return 0;
+ exe_file = get_mm_exe_file(mm);
+ mmput(mm);
+ 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);
}
--
1.7.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] audit: fix audit_exe_compare using get_mm_exe_file
2016-08-22 15:41 [PATCH] audit: fix audit_exe_compare using get_mm_exe_file Richard Guy Briggs
@ 2016-08-22 16:27 ` Mateusz Guzik
0 siblings, 0 replies; 2+ messages in thread
From: Mateusz Guzik @ 2016-08-22 16:27 UTC (permalink / raw)
To: Richard Guy Briggs
Cc: linux-audit, linux-kernel, ebiederm, oleg, skinsbursky, luto,
sgrubb, pmoore, eparis
On Mon, Aug 22, 2016 at 11:41:34AM -0400, Richard Guy Briggs wrote:
> Fix original naive attempt to get/lock access to task->mm->exe_file by
> using get_mm_exe_file and checking for NULL.
>
> See: https://lkml.org/lkml/2016/7/30/97
>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
> kernel/audit_watch.c | 13 ++++++++++---
> 1 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
> index d6709eb..0b29279 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>
> @@ -540,14 +541,20 @@ int audit_dupe_exe(struct audit_krule *new, struct audit_krule *old)
>
> int audit_exe_compare(struct task_struct *tsk, struct audit_fsnotify_mark *mark)
> {
> + struct mm_struct *mm;
> struct file *exe_file;
> unsigned long ino;
> dev_t dev;
>
> - rcu_read_lock();
> - exe_file = rcu_dereference(tsk->mm->exe_file);
> + mm = get_task_mm(tsk);
> + if (!mm)
> + return 0;
> + exe_file = get_mm_exe_file(mm);
> + mmput(mm);
> + 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);
> }
I think this works but I have a better idea. This basically duplicates a
part of proc_exe_link and does unnecessary work.
Instead, one can introduce get_task_exe_file. task_lock held guarantees
the stability of mm struct itself, and then we can we can try to grab
the file without mm refcount dance.
I'll implement this later today.
--
Mateusz Guzik
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2016-08-22 16:27 ` Mateusz Guzik
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