Re: [PATCH v3] Bluetooth: call lock_sock() outside of spinlock section
From: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date: 2021-07-14 19:20:29
Also in:
netdev
Hi Tetsuo, On Tue, Jul 13, 2021 at 4:28 AM Tetsuo Handa [off-list ref] 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@i-love.sakura.ne.jp [2] Reported-by: syzbot <redacted> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Tested-by: syzbot <redacted> 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@gmail.com/
quoted hunk ↗ jump to hunk
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