Hi Tetsuo, On Tue, Jul 13, 2021 at 4:28 AM Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > syzbot is hitting might_sleep() warning at hci_sock_dev_event() due to > calling lock_sock() with rw spinlock held [1]. Among three possible > approaches [2], this patch chose holding a refcount via sock_hold() and > revalidating the element via sk_hashed(). > > Link: https://syzkaller.appspot.com/bug?extid=a5df189917e79d5e59c9 [1] > Link: https://lkml.kernel.org/r/05535d35-30d6-28b6-067e-272d01679d24@xxxxxxxxxxxxxxxxxxx [2] > Reported-by: syzbot <syzbot+a5df189917e79d5e59c9@xxxxxxxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Tested-by: syzbot <syzbot+a5df189917e79d5e59c9@xxxxxxxxxxxxxxxxxxxxxxxxx> > Fixes: e305509e678b3a4a ("Bluetooth: use correct lock to prevent UAF of hdev object") > --- > Changes in v3: > Don't use unlocked hci_pi(sk)->hdev != hdev test, for it is racy. > No need to defer hci_dev_put(hdev), for it can't be the last reference. > > Changes in v2: > Take hci_sk_list.lock for write in case bt_sock_unlink() is called after > sk_hashed(sk) test, and defer hci_dev_put(hdev) till schedulable context. How about we revert back to use bh_lock_sock_nested but use local_bh_disable like the following patch: https://patchwork.kernel.org/project/bluetooth/patch/20210713162838.693266-1-desmondcheongzx@xxxxxxxxx/ > net/bluetooth/hci_sock.c | 30 +++++++++++++++++++++++++++++- > 1 file changed, 29 insertions(+), 1 deletion(-) > > diff --git a/net/bluetooth/hci_sock.c b/net/bluetooth/hci_sock.c > index b04a5a02ecf3..786a06a232fd 100644 > --- a/net/bluetooth/hci_sock.c > +++ b/net/bluetooth/hci_sock.c > @@ -760,10 +760,18 @@ void hci_sock_dev_event(struct hci_dev *hdev, int event) > struct sock *sk; > > /* Detach sockets from device */ > +restart: > read_lock(&hci_sk_list.lock); > sk_for_each(sk, &hci_sk_list.head) { > + /* This sock_hold(sk) is safe, for bt_sock_unlink(sk) > + * is not called yet. > + */ > + sock_hold(sk); > + read_unlock(&hci_sk_list.lock); > lock_sock(sk); > - if (hci_pi(sk)->hdev == hdev) { > + write_lock(&hci_sk_list.lock); > + /* Check that bt_sock_unlink(sk) is not called yet. */ > + if (sk_hashed(sk) && hci_pi(sk)->hdev == hdev) { > hci_pi(sk)->hdev = NULL; > sk->sk_err = EPIPE; > sk->sk_state = BT_OPEN; > @@ -771,7 +779,27 @@ void hci_sock_dev_event(struct hci_dev *hdev, int event) > > hci_dev_put(hdev); > } > + write_unlock(&hci_sk_list.lock); > release_sock(sk); > + read_lock(&hci_sk_list.lock); > + /* If bt_sock_unlink(sk) is not called yet, we can > + * continue iteration. We can use __sock_put(sk) here > + * because hci_sock_release() will call sock_put(sk) > + * after bt_sock_unlink(sk). > + */ > + if (sk_hashed(sk)) { > + __sock_put(sk); > + continue; > + } > + /* Otherwise, we need to restart iteration, for the > + * next socket pointed by sk->next might be already > + * gone. We can't use __sock_put(sk) here because > + * hci_sock_release() might have already called > + * sock_put(sk) after bt_sock_unlink(sk). > + */ > + read_unlock(&hci_sk_list.lock); > + sock_put(sk); > + goto restart; > } > read_unlock(&hci_sk_list.lock); > } > -- > 2.18.4 > -- Luiz Augusto von Dentz
