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

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(a)suse.de&gt; --- changes from v1: rebased on top of 1/1. kernel/audit.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-)

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)