From 45e4d11fa6f4b019553893e8ed20a1b6d461103b Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 11 Mar 2020 11:53:09 +0100 Subject: [PATCH] binderfs: use refcount for binder control devices too Binderfs binder-control devices are cleaned up via binderfs_evict_inode too() which will use refcount_dec_and_test(). However, we missed to set the refcount for binderfs binder-control devices and so we underflowed when the binderfs instance got unmounted. Pretty obvious oversight and should have been part of the more general UAF fix. The good news is that having test cases (suprisingly) helps. Technically, we could detect that we're about to cleanup the binder-control dentry in binderfs_evict_inode() and then simply clean it up. But that makes the assumption that the binder driver itself will never make use of a binderfs binder-control device after the binderfs instance it belongs to has been unmounted and the superblock for it been destroyed. While it is unlikely to ever come to this let's be on the safe side. Performance-wise this also really doesn't matter since the binder-control device is only every really when creating the binderfs filesystem or creating additional binder devices. Both operations are pretty rare. Fixes: f0fe2c0f050d ("binder: prevent UAF for binderfs devices II") Link: https://lore.kernel.org/r/CA+G9fYusdfg7PMfC9Xce-xLT7NiyKSbgojpK35GOm=Pf9jXXrA@mail.gmail.com Reported-by: Naresh Kamboju Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner Acked-by: Todd Kjos Link: https://lore.kernel.org/r/20200311105309.1742827-1-christian.brauner@ubuntu.com Signed-off-by: Greg Kroah-Hartman --- drivers/android/binderfs.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c index 14a4bef358cd..3fd7cf48c39e 100644 --- a/drivers/android/binderfs.c +++ b/drivers/android/binderfs.c @@ -448,6 +448,7 @@ static int binderfs_binder_ctl_create(struct super_block *sb) inode->i_uid = info->root_uid; inode->i_gid = info->root_gid; + refcount_set(&device->ref, 1); device->binderfs_inode = inode; device->miscdev.minor = minor;