cgroup: fix use-after-free when umounting cgroupfs

PATCH Applied Li Zefan 2 participants 2 messages Apr 26, 2013 cgroup

lore

Share & tools

lore

Li Zefan

author

2013-04-26 02:54 UTC #0 lore raw

PATCH 1/1 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 <[email protected]>

---
 kernel/cgroup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

kernel/cgroup.c +4 -2

index 6780459..a45aa12 100644
@@ -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);
 }

Signature · 1 line

1.8.0.2

Tejun Heo

maintainer Applied

2013-04-26 18:59 UTC #1 lore raw

Quoted 6 lines · Li Zefan

Try:

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

And you might see this:

Quoted 7 lines

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 <[email protected]>

Applied to cgroup/for-3.10.

Thanks.

Signature · 1 line

tejun