linux-kernel - [PATCH 3.2 050/164] fs: Fix theoretical division by 0 in super_cache

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Date:	Fri, 12 Dec 2014 06:14:25 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Christoph Hellwig" <hch@....de>,
	"Al Viro" <viro@...iv.linux.org.uk>,
	"Tetsuo Handa" <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [PATCH 3.2 050/164] fs: Fix theoretical division by 0 in
 super_cache_scan().

3.2.65-rc1 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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/super.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/fs/super.c
+++ b/fs/super.c
@@ -68,6 +68,8 @@ static int prune_super(struct shrinker *
 
 	total_objects = sb->s_nr_dentry_unused +
 			sb->s_nr_inodes_unused + fs_objects + 1;
+	if (!total_objects)
+		total_objects = 1;
 
 	if (sc->nr_to_scan) {
 		int	dentries;

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