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

Paul Moore
2015-02-23T21:59:25Z

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@suse.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