linux-kernel - [009/118] cgroup: fix an off-by-one bug which may trigger BUG

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Message-ID: <lsq.1368193181.351454482@decadent.org.uk>
Date:	Fri, 10 May 2013 14:39:41 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Tejun Heo" <tj@...nel.org>,
	"Li Zefan" <lizefan@...wei.com>
Subject: [009/118] cgroup: fix an off-by-one bug which may trigger BUG_ON()

3.2.45-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Li Zefan <lizefan@...wei.com>

commit 3ac1707a13a3da9cfc8f242a15b2fae6df2c5f88 upstream.

The 3rd parameter of flex_array_prealloc() is the number of elements,
not the index of the last element.

The effect of the bug is, when opening cgroup.procs, a flex array will
be allocated and all elements of the array is allocated with
GFP_KERNEL flag, but the last one is GFP_ATOMIC, and if we fail to
allocate memory for it, it'll trigger a BUG_ON().

Signed-off-by: Li Zefan <lizefan@...wei.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2029,7 +2029,7 @@ int cgroup_attach_proc(struct cgroup *cg
 	if (!group)
 		return -ENOMEM;
 	/* pre-allocate to guarantee space while iterating in rcu read-side. */
-	retval = flex_array_prealloc(group, 0, group_size - 1, GFP_KERNEL);
+	retval = flex_array_prealloc(group, 0, group_size, GFP_KERNEL);
 	if (retval)
 		goto out_free_group_list;
 

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