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References: <20221105190446.1324053-1-syoshida@redhat.com>
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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Mon, 7 Nov 2022 10:49:48 -0800
Message-ID: <CABBYNZLqk_4Xz3RuSq_cEhvyTG+Qz1icVKjvKunufCLLXhh_zg@mail.gmail.com>
Subject: Re: [PATCH] Bluetooth: Fix use-after-free read in hci_cmd_timeout()
To:     Shigeru Yoshida <syoshida@redhat.com>
Cc:     marcel@holtmann.org, johan.hedberg@gmail.com,
        linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        syzbot+19a9f729f05272857487@syzkaller.appspotmail.com
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Hi Shigeru,

On Sat, Nov 5, 2022 at 12:04 PM Shigeru Yoshida <syoshida@redhat.com> wrote:
>
> syzbot reported use-after-free in hci_cmd_timeout() [1].  The scenario
> for the issue is as follows:
>
> Task                                    Workqueue
> ----------------------------------------------------------------------
> hci_dev_open_sync
>   ...
>   hci_dev_init_sync  <- failed
>   ...
>   if (hdev->sent_cmd)
>     kfree_skb(hdev->sent_cmd)
>                                         hci_cmd_timeout
>                                           ...
>                                           if (hdev->sent_cmd)
>                                             sent = hdev->sent_cmd->data
>                                                    ^^ UAF occurred
>     hdev->sent_cmd = NULL
>
> When hci_dev_init_sync() failed, hci_dev_open_sync() frees
> hdev->send_cmd and set it to NULL.  However, hci_cmd_timeout() can run
> just after freeing hdev->sent_cmd because hdev->cmd_timer is not
> canceled.
>
> This patch fixes the issue by canceling hdev->cmd_timer before freeing
> hdev->sent_cmd.
>
> Link: https://syzkaller.appspot.com/bug?id=cb23ebfc8f304f510fb717cb783fe8b496c7ffb1 [1]
> Reported-by: syzbot+19a9f729f05272857487@syzkaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> ---
>  net/bluetooth/hci_sync.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 76c3107c9f91..a011065220e4 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -4696,6 +4696,7 @@ int hci_dev_open_sync(struct hci_dev *hdev)
>                         hdev->flush(hdev);
>
>                 if (hdev->sent_cmd) {
> +                       cancel_delayed_work_sync(&hdev->cmd_timer);
>                         kfree_skb(hdev->sent_cmd);
>                         hdev->sent_cmd = NULL;
>                 }
> --
> 2.38.1

A similar fix has already been applied:

https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=64b5c4c8e79c131fe8f135bab5e5dfaa245c5776


-- 
Luiz Augusto von Dentz