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cgroup: fix use-after-free when umounting cgroupfs 

Try:
  # mount -t cgroup xxx /cgroup
  # mkdir /cgroup/sub && rmdir /cgroup/sub && umount /cgroup

And you might see this:

ida_remove called for id=1 which is not allocated.

It's because cgroup_kill_sb() is called to destroy root->cgroup_ida
and free cgrp->root before ida_simple_removed() is called. What's
worse is we're accessing cgrp->root while it has been freed.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Li Zefan 2013-04-26 11:58:02 -07:00 committed by Tejun Heo
parent 712317ad97
commit cc20e01cd6
1 changed files with 4 additions and 2 deletions
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6
kernel/cgroup.c
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@ -848,9 +848,12 @@ static void cgroup_free_fn(struct work_struct *work)
*/ */
dput(cgrp->parent->dentry); dput(cgrp->parent->dentry);
ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
/* /*
* Drop the active superblock reference that we took when we * Drop the active superblock reference that we took when we
* created the cgroup * created the cgroup. This will free cgrp->root, if we are
* holding the last reference to @sb.
*/ */
deactivate_super(cgrp->root->sb); deactivate_super(cgrp->root->sb);
@ -862,7 +865,6 @@ static void cgroup_free_fn(struct work_struct *work)
simple_xattrs_free(&cgrp->xattrs); simple_xattrs_free(&cgrp->xattrs);
ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
kfree(rcu_dereference_raw(cgrp->name)); kfree(rcu_dereference_raw(cgrp->name));
kfree(cgrp); kfree(cgrp);
} }