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

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jan 21, 2019 at 03:51:11PM +0100, Marcel Holtmann wrote:
> Hi Greg,
> 
> >>>> 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:
> >> 
> >> it would be still good if we can get this verified by the reporter.
> > 
> > The "reporter" seems to have disappeared once they reported this stuff,
> > so I would not count on them doing anything here, we asked numerous
> > times :(
> > 
> > If the patches look correct, I recommend just merging it and I can
> > backport it to the stable releases and the distros can pick it up from
> > there.
> 
> I think that I have Johan merge them into bluetooth-next first and let
> them sit a little so we can verify they do not break anything else.
> You can pick them up later into -stable if nobody complained and we
> didn’t break qualification.

Sounds good to me, thanks.

greg k-h