[PATCH v3 3/3] tomoyo: reduce mmap_sem hold for mm->exe_file

Davidlohr Bueso
2015-02-24T19:42:59Z

The mm->exe_file is currently serialized with mmap_sem (shared) in order
to both safely (1) read the file and (2) compute the realpath by calling
tomoyo_realpath_from_path, making it an absolute overkill. 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

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---

Changes from v2: remove cleanups and cp initialization.

security/tomoyo/util.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/security/tomoyo/util.c b/security/tomoyo/util.c
index 2952ba5..29f3b65 100644
--- a/security/tomoyo/util.c
+++ b/security/tomoyo/util.c
@@ -948,16 +948,19 @@ bool tomoyo_path_matches_pattern(const struct tomoyo_path_info *filename,
*/
const char *tomoyo_get_exe(void)
{
- struct mm_struct *mm = current->mm;
- const char *cp = NULL;
+ struct file *exe_file;
+ const char *cp;
+ struct mm_struct *mm = current->mm;

- if (!mm)
- return NULL;
- down_read(&mm->mmap_sem);
- if (mm->exe_file)
- cp = tomoyo_realpath_from_path(&mm->exe_file->f_path);
- up_read(&mm->mmap_sem);
- return cp;
+ if (!mm)
+ return NULL;
+ exe_file = get_mm_exe_file(mm);
+ if (!exe_file)
+ return NULL;
+
+ cp = tomoyo_realpath_from_path(&exe_file->f_path);
+ fput(exe_file);
+ return cp;
}

/**
--
2.1.4