linux-kernel - Re: [PATCH] Bluetooth: Fix skb allocation in mgmt_remote

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Date:   Thu, 13 Jan 2022 23:07:02 +0100
From:   Radosław Biernacki <rad@...ihalf.com>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc:     linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        CrosBT Upstreaming <chromeos-bluetooth-upstreaming@...omium.org>,
        Archie Pusaka <apusaka@...omium.org>,
        Miao-chen Chou <mcchou@...omium.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        upstream@...ihalf.com, Angela Czubak <acz@...ihalf.com>,
        Marek Maslanka <mm@...ihalf.com>
Subject: Re: [PATCH] Bluetooth: Fix skb allocation in mgmt_remote_name()

Hi Luiz,

czw., 13 sty 2022 o 17:17 Luiz Augusto von Dentz
<luiz.dentz@...il.com> napisał(a):
>
> Hi Radoslaw,
>
> On Thu, Jan 13, 2022 at 7:09 AM Radoslaw Biernacki <rad@...ihalf.com> wrote:
> >
> > From: Radoslaw Biernacki <rad@...ihalf.com>
> >
> > This patch fixes skb allocation, as lack of space for ev might push skb
> > tail beyond its end.
> > Also introduce eir_precalc_len() that can be used instead of magic
> > numbers for similar eir operations on skb.
> >
> > Fixes: cf1bce1de7eeb ("Bluetooth: mgmt: Make use of mgmt_send_event_skb in MGMT_EV_DEVICE_FOUND")
> > Signed-off-by: Angela Czubak <acz@...ihalf.com>
> > Signed-off-by: Marek Maslanka <mm@...ihalf.com>
> > Signed-off-by: Radoslaw Biernacki <rad@...ihalf.com>
> > ---
> >  net/bluetooth/eir.h  |  5 +++++
> >  net/bluetooth/mgmt.c | 12 ++++--------
> >  2 files changed, 9 insertions(+), 8 deletions(-)
> >
> > diff --git a/net/bluetooth/eir.h b/net/bluetooth/eir.h
> > index 05e2e917fc25..e5876751f07e 100644
> > --- a/net/bluetooth/eir.h
> > +++ b/net/bluetooth/eir.h
> > @@ -15,6 +15,11 @@ u8 eir_create_scan_rsp(struct hci_dev *hdev, u8 instance, u8 *ptr);
> >  u8 eir_append_local_name(struct hci_dev *hdev, u8 *eir, u8 ad_len);
> >  u8 eir_append_appearance(struct hci_dev *hdev, u8 *ptr, u8 ad_len);
> >
> > +static inline u16 eir_precalc_len(u8 data_len)
> > +{
> > +       return sizeof(u8) * 2 + data_len;
> > +}
> > +
> >  static inline u16 eir_append_data(u8 *eir, u16 eir_len, u8 type,
> >                                   u8 *data, u8 data_len)
> >  {
> > diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
> > index 37087cf7dc5a..d517fd847730 100644
> > --- a/net/bluetooth/mgmt.c
> > +++ b/net/bluetooth/mgmt.c
> > @@ -9680,13 +9680,11 @@ void mgmt_remote_name(struct hci_dev *hdev, bdaddr_t *bdaddr, u8 link_type,
> >  {
> >         struct sk_buff *skb;
> >         struct mgmt_ev_device_found *ev;
> > -       u16 eir_len;
> > -       u32 flags;
> > +       u16 eir_len = 0;
> > +       u32 flags = 0;
> >
> > -       if (name_len)
> > -               skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND, 2 + name_len);
> > -       else
> > -               skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND, 0);
> > +       skb = mgmt_alloc_skb(hdev, MGMT_EV_DEVICE_FOUND,
> > +                            sizeof(*ev) + (name ? eir_precalc_len(name_len) : 0));
>
> Looks like mgmt_device_connected also has a similar problem.

Yes, I was planning to send a patch to this one though it will not be as slick.
It would be nice to have a helper which will call skb_put() and add
eir data at once.
Basically skb operation in pair to, what eir_append_data() does with
help of eir_len but without awkwardness when passing return value to
skb_put() (as it returns offset not size).
I will send V2 with two patches. I hope they will align with your
original goal of eliminating the necessity of intermediary buffers at
some point in future.

>
> >         ev = skb_put(skb, sizeof(*ev));
> >         bacpy(&ev->addr.bdaddr, bdaddr);
> > @@ -9696,10 +9694,8 @@ void mgmt_remote_name(struct hci_dev *hdev, bdaddr_t *bdaddr, u8 link_type,
> >         if (name) {
> >                 eir_len = eir_append_data(ev->eir, 0, EIR_NAME_COMPLETE, name,
> >                                           name_len);
> > -               flags = 0;
> >                 skb_put(skb, eir_len);
> >         } else {
> > -               eir_len = 0;
> >                 flags = MGMT_DEV_FOUND_NAME_REQUEST_FAILED;
> >         }
>
> These changes would leave flags and eir_len uninitialized.

Both are initialized to 0 by this patch.

>
> > --
> > 2.34.1.703.g22d0c6ccf7-goog
> >
>
>
> --
> Luiz Augusto von Dentz