Re: [PATCH] Bluetooth: Verify that l2cap_get_conf_opt provides large enough buffer

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jan 18, 2019 at 01:43:19PM +0100, Marcel Holtmann wrote:
> The function l2cap_get_conf_opt will return L2CAP_CONF_OPT_SIZE + opt->len
> as length value. The opt->len however is in control over the remote user
> and can be used by an attacker to gain access beyond the bounds of the
> actual packet.
> 
> To prevent any potential leak of heap memory, it is enough to check that
> the resulting len calculation after calling l2cap_get_conf_opt is not
> below zero. A well formed packet will always return >= 0 here and will
> end with the length value being zero after the last option has been
> parsed. In case of malformed packets messing with the opt->len field the
> length value will become negative. If that is the case, then just abort
> and ignore the option.
> 
> In case an attacker uses a too short opt->len value, then garbage will
> be parsed, but that is protected by the unknown option handling and also
> the option parameter size checks.
> 
> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
> ---
>  net/bluetooth/l2cap_core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 77799e7d5a34..ccdc5c67d22a 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -3337,6 +3337,8 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>  
>  	while (len >= L2CAP_CONF_OPT_SIZE) {
>  		len -= l2cap_get_conf_opt(&req, &type, &olen, &val);
> +		if (len < 0)
> +			break;

<snip>

Patch looks good to me, thanks for fixing this all up:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>