releases/3.17.3/fs-fix-theoretical-division-by-0-in-super_cache_scan.patch

From 475d0db742e3755c6b267f48577ff7cbb7dfda0d Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 17 May 2014 20:56:38 +0900
Subject: fs: Fix theoretical division by 0 in super_cache_scan().

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit 475d0db742e3755c6b267f48577ff7cbb7dfda0d upstream.

total_objects could be 0 and is used as a denom.

While total_objects is a "long", total_objects == 0 unlikely happens for
3.12 and later kernels because 32-bit architectures would not be able to
hold (1 << 32) objects. However, total_objects == 0 may happen for kernels
between 3.1 and 3.11 because total_objects in prune_super() was an "int"
and (e.g.) x86_64 architecture might be able to hold (1 << 32) objects.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/super.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/super.c
+++ b/fs/super.c
@@ -80,6 +80,8 @@ static unsigned long super_cache_scan(st
 	inodes = list_lru_count_node(&sb->s_inode_lru, sc->nid);
 	dentries = list_lru_count_node(&sb->s_dentry_lru, sc->nid);
 	total_objects = dentries + inodes + fs_objects + 1;
+	if (!total_objects)
+		total_objects = 1;
 
 	/* proportion the scan between the caches */
 	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);