linux-kernel - [PATCH v3 3/3] tomoyo: reduce mmap_sem hold for mm->exe

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Date:	Tue, 24 Feb 2015 11:42:46 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	akpm@...ux-foundation.org, dave@...olabs.net, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, takedakn@...data.co.jp,
	linux-security-module@...r.kernel.org,
	tomoyo-dev-en@...ts.sourceforge.jp
Subject: [PATCH v3 3/3] 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

Signed-off-by: Davidlohr Bueso <dbueso@...e.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



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