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Subject: Re: [Linux-kernel-mentees] [PATCH] Fix uninit-value in
 hci_chan_lookup_handle
To:     linux-kernel-mentees@lists.linuxfoundation.org
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200905020410.20350-1-anant.thazhemadam@gmail.com>
From:   Anant Thazhemadam <anant.thazhemadam@gmail.com>
Message-ID: <b7c54f39-976c-644b-a451-83d8d508f0bb@gmail.com>
Date:   Fri, 25 Sep 2020 23:30:50 +0530
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On 05/09/20 7:34 am, Anant Thazhemadam wrote:
> When the amount of data stored in the location corresponding to
> iov_iter *from is less then 4, some data seems to go uninitialized.
>
> Updating this condition accordingly, makes sense both intuitively and 
> logically as well, since the other check for extreme condition done is if
> len > HCI_MAX_FRAME_SIZE, which is HCI_MAX_ACL_SIZE (which is 1024) + 4;
> which itself gives some idea about what must be the ideal mininum size.
>
> Reported-and-tested by: syzbot+4c14a8f574461e1c3659@syzkaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
> ---
> If there is some explicit reason why len < 4 doesn't work, and only len < 2 works, 
> please do let me know.
> The commit message that introduced the initial change 
> (512b2268156a4e15ebf897f9a883bdee153a54b7) wasn't exactly very helpful in this 
> respect, and I couldn't find a whole lot of discussion regarding this either.
>
>  drivers/bluetooth/hci_vhci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
> index 8ab26dec5f6e..0c49821d7b98 100644
> --- a/drivers/bluetooth/hci_vhci.c
> +++ b/drivers/bluetooth/hci_vhci.c
> @@ -159,7 +159,7 @@ static inline ssize_t vhci_get_user(struct vhci_data *data,
>  	__u8 pkt_type, opcode;
>  	int ret;
>  
> -	if (len < 2 || len > HCI_MAX_FRAME_SIZE)
> +	if (len < 4 || len > HCI_MAX_FRAME_SIZE)
>  		return -EINVAL;
>  
>  	skb = bt_skb_alloc(len, GFP_KERNEL);
Hi,

Looks like this patch might have missed the attention of those
who can tell me if this works or why it might not.
For some more context; more details about the bug can be found at
??? https://syzkaller.appspot.com/bug?id=287b84cc1c834c7878c4193d7b18760067f10a77
I should've highlighted that in my initial mail. My apologies.

Thanks,
Anant