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

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Date:	Mon, 23 Feb 2015 16:59:19 -0500
From:	Paul Moore <paul@...l-moore.com>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, eparis@...hat.com,
	linux-audit@...hat.com
Subject: Re: [PATCH v2 2/3] kernel/audit: reduce mmap_sem hold for mm->exe_file

On Sunday, February 22, 2015 06:20:09 PM Davidlohr Bueso wrote:
> 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@...e.de>
> ---
> 
> changes from v1: rebased on top of 1/1.
> 
>  kernel/audit.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)

Merged into audit#next.

> 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)

-- 
paul moore
www.paul-moore.com

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