From: Christian Brauner christian.brauner@ubuntu.com
[ Upstream commit 211b64e4b5b6bd5fdc19cd525c2cc9a90e6b0ec9 ]
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=Pf9jXXr... Reported-by: Naresh Kamboju naresh.kamboju@linaro.org Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner christian.brauner@ubuntu.com Acked-by: Todd Kjos tkjos@google.com Link: https://lore.kernel.org/r/20200311105309.1742827-1-christian.brauner@ubuntu.... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/android/binderfs.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c index 110e41f920c27..f303106b3362b 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;