tomoyo: 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) 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

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/security/tomoyo/util.c b/security/tomoyo/util.c
index 2952ba576fb9ceed3f64c23663a2b40f3cfbe13e..b974a6997d7f8b7a81f8d2062c59a810b0a6c2d7 100644 (file)
--- a/security/tomoyo/util.c
+++ b/security/tomoyo/util.c
@@ -948,15 +948,18 @@ bool tomoyo_path_matches_pattern(const struct tomoyo_path_info *filename,
  */
 const char *tomoyo_get_exe(void)
 {
+       struct file *exe_file;
+       const char *cp;
        struct mm_struct *mm = current->mm;
-       const char *cp = NULL;
 
        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);
+       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;
 }