linux-kernel - [ 33/46] cgroup: fix an off-by-one bug which may trigger BUG

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Message-Id: <20130506225824.144630895@linuxfoundation.org>
Date:	Mon,  6 May 2013 15:58:39 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
	Tejun Heo <tj@...nel.org>
Subject: [ 33/46] cgroup: fix an off-by-one bug which may trigger BUG_ON()

3.0-stable 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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/cgroup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2026,7 +2026,7 @@ 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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