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

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jan 18, 2019 at 02:12:23PM +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.

thanks,

greg k-h