netdev - Re: [PATCH] Bluetooth: add timeout sanity check to hci

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Date:   Thu, 19 Aug 2021 17:05:41 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+be2baed593ea56c6a84c@...kaller.appspotmail.com
Subject: Re: [PATCH] Bluetooth: add timeout sanity check to hci_inquiry

Hi Pavel,

> Syzbot hit "task hung" bug in hci_req_sync(). The problem was in
> unreasonable huge inquiry timeout passed from userspace.
> Fix it by adding sanity check for timeout value and add constant to
> hsi_sock.h to inform userspace, that hci_inquiry_req::length field has
> maximum possible value.
> 
> Since hci_inquiry() is the only user of hci_req_sync() with user
> controlled timeout value, it makes sense to check timeout value in
> hci_inquiry() and don't touch hci_req_sync().
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-and-tested-by: syzbot+be2baed593ea56c6a84c@...kaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> ---
> 
> Hi, Bluetooth maintainers/reviewers!
> 
> I believe, 60 seconds will be more than enough for inquiry request. I've
> searched for examples on the internet and maximum ir.length I found was 
> 8. Maybe, we have users, which need more than 60 seconds... I look forward
> to receiving your views on this value.
> 
> ---
> include/net/bluetooth/hci_sock.h | 1 +
> net/bluetooth/hci_core.c         | 5 +++++
> 2 files changed, 6 insertions(+)
> 
> diff --git a/include/net/bluetooth/hci_sock.h b/include/net/bluetooth/hci_sock.h
> index 9949870f7d78..1cd63d4da00b 100644
> --- a/include/net/bluetooth/hci_sock.h
> +++ b/include/net/bluetooth/hci_sock.h
> @@ -168,6 +168,7 @@ struct hci_inquiry_req {
> 	__u16 dev_id;
> 	__u16 flags;
> 	__u8  lap[3];
> +#define HCI_INQUIRY_MAX_TIMEOUT		30
> 	__u8  length;
> 	__u8  num_rsp;
> };
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index e1a545c8a69f..104babf67351 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -1343,6 +1343,11 @@ int hci_inquiry(void __user *arg)
> 		goto done;
> 	}
> 

	/* Restrict maximum inquiry length to 60 seconds */
	if (ir.length > 60) {
		..
	}

> +	if (ir.length > HCI_INQUIRY_MAX_TIMEOUT) {
> +		err = -EINVAL;
> +		goto done;
> +	}
> +

I found this easier to read than adding anything define somewhere else. And since this is a legacy interface that is no longer used by bluetoothd, this should be fine. We will start to deprecate this eventually.

And I prefer 1 minute max time here. Just to be safe.

Regards

Marcel