cgroup: fix an off-by-one bug which may trigger BUG_ON()

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@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c0739f8..d2a01fe 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2029,7 +2029,7 @@ 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;