linux-kernel - [PATCH] fs: Fix theoretical division by 0 in super_cache

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Message-Id: <201406232124.CCG86436.SFtOJOFLVOHFMQ@I-love.SAKURA.ne.jp>
Date:	Mon, 23 Jun 2014 21:24:46 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	viro@...IV.linux.org.uk
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs: Fix theoretical division by 0 in super_cache_scan().

>>From 7a2ed4e9c91864736ce5ad89489fd5862d59542e Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Sat, 17 May 2014 20:56:38 +0900
Subject: [PATCH] fs: Fix theoretical division by 0 in super_cache_scan().

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@...ove.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@....de>
Cc: stable <stable@...nel.org> # 3.1+
---
 fs/super.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 48377f7..1408362 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -81,6 +81,8 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	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);
-- 
1.7.1
--
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