linux-kernel - [PATCH 3.16.y-ckt 085/254] fs: Fix theoretical division by 0 in super_cache

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Message-Id: <1416912004-5928-86-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 25 Nov 2014 10:37:15 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Al Viro <viro@...iv.linux.org.uk>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 085/254] fs: Fix theoretical division by 0 in super_cache_scan().

3.16.7-ckt2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@...ove.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@...ove.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index d20d5b11dedf..abb8c7f9599b 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);
-- 
2.1.0

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