Messages in this thread Patch in this message | | | Date | Fri, 26 Apr 2013 10:54:11 +0800 | From | Li Zefan <> | Subject | [PATCH] cgroup: fix use-after-free when umounting cgroupfs |
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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> --- kernel/cgroup.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6780459..a45aa12 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -845,9 +845,12 @@ static void cgroup_free_fn(struct work_struct *work) */ dput(cgrp->parent->dentry); + ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id); + /* * 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); @@ -859,7 +862,6 @@ static void cgroup_free_fn(struct work_struct *work) simple_xattrs_free(&cgrp->xattrs); - ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id); kfree(rcu_dereference_raw(cgrp->name)); kfree(cgrp); } -- 1.8.0.2
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