Patchwork [067/118] cgroup: fix an off-by-one bug which may trigger BUG_ON()

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Submitter Luis Henriques
Date May 7, 2013, 1:38 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/242295/
State New
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Luis Henriques - May 7, 2013, 1:38 p.m. -stable review patch.  If anyone has any objections, please let me know.


From: Li Zefan <>

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 <>
Signed-off-by: Tejun Heo <>
Signed-off-by: Luis Henriques <>
 kernel/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 87fbb45..5168e37 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2079,7 +2079,7 @@  static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 	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;