Bluetooth: btusb: use skb_pull to avoid unsafe access in QCA dump handling

Use skb_pull() and skb_pull_data() to safely parse QCA dump packets.

This avoids direct pointer math on skb->data, which could lead to
invalid access if the packet is shorter than expected.

Signed-off-by: En-Wei Wu <en-wei.wu@canonical.com>
---
 drivers/bluetooth/btusb.c | 99 ++++++++++++++++-----------------------
 1 file changed, 41 insertions(+), 58 deletions(-)

Hi Paul,

> Also, how did you test this?
I triggered the device coredump by `$ echo 1` to the file named
"coredump" in the sysfs device node of the hci device. The symbolic
link of the file can be found at
/sys/class/bluetooth/hci*/device/coredump.
After triggering the coredump, the core dump file can be found at
/sys/class/devcoredump.

Kind regards,
En-Wei

On Tue, 6 May 2025 at 16:46, Paul Menzel <pmenzel@molgen.mpg.de> wrote:
>
> Dear En-Wei,
>
>
> Thank you for your patch.
>
> Am 06.05.25 um 04:48 schrieb En-Wei Wu:
> > Use skb_pull() and skb_pull_data() to safely parse QCA dump packets.
> >
> > This avoids direct pointer math on skb->data, which could lead to
> > invalid access if the packet is shorter than expected.
>
> Please add a Fixes: tag.
>
> Also, how did you test this?
>
> > Signed-off-by: En-Wei Wu <en-wei.wu@canonical.com>
> > ---
> >   drivers/bluetooth/btusb.c | 99 ++++++++++++++++-----------------------
> >   1 file changed, 41 insertions(+), 58 deletions(-)
> >
> > diff --git a/drivers/bluetooth/btusb.c b/drivers/bluetooth/btusb.c
> > index 357b18dae8de..17136924a278 100644
> > --- a/drivers/bluetooth/btusb.c
> > +++ b/drivers/bluetooth/btusb.c
> > @@ -2979,9 +2979,8 @@ static void btusb_coredump_qca(struct hci_dev *hdev)
> >   static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >   {
> >       int ret = 0;
> > +     int skip = 0;
>
> `unsigned int`, as the signature is:
>
>      include/linux/skbuff.h:void *skb_pull(struct sk_buff *skb, unsigned
> int len);
>
> >       u8 pkt_type;
> > -     u8 *sk_ptr;
> > -     unsigned int sk_len;
> >       u16 seqno;
> >       u32 dump_size;
> >
> > @@ -2990,18 +2989,14 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >       struct usb_device *udev = btdata->udev;
> >
> >       pkt_type = hci_skb_pkt_type(skb);
> > -     sk_ptr = skb->data;
> > -     sk_len = skb->len;
> > -
> > -     if (pkt_type == HCI_ACLDATA_PKT) {
> > -             sk_ptr += HCI_ACL_HDR_SIZE;
> > -             sk_len -= HCI_ACL_HDR_SIZE;
> > -     }
> > +     if (pkt_type == HCI_ACLDATA_PKT)
> > +             skip = sizeof(struct hci_acl_hdr) + sizeof(struct hci_event_hdr);
> > +     else
> > +             skip = sizeof(struct hci_event_hdr);
>
> Maybe write it as below:
>
>      skip = sizeof(struct hci_event_hdr);
>
>      if (pkt_type == HCI_ACLDATA_PKT)
>         skip += sizeof(struct hci_acl_hdr);
>
>
> Kind regards,
>
> Paul
>
>
> >
> > -     sk_ptr += HCI_EVENT_HDR_SIZE;
> > -     sk_len -= HCI_EVENT_HDR_SIZE;
> > +     skb_pull(skb, skip);
> > +     dump_hdr = (struct qca_dump_hdr *)skb->data;
> >
> > -     dump_hdr = (struct qca_dump_hdr *)sk_ptr;
> >       seqno = le16_to_cpu(dump_hdr->seqno);
> >       if (seqno == 0) {
> >               set_bit(BTUSB_HW_SSR_ACTIVE, &btdata->flags);
> > @@ -3021,16 +3016,15 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >
> >               btdata->qca_dump.ram_dump_size = dump_size;
> >               btdata->qca_dump.ram_dump_seqno = 0;
> > -             sk_ptr += offsetof(struct qca_dump_hdr, data0);
> > -             sk_len -= offsetof(struct qca_dump_hdr, data0);
> > +
> > +             skb_pull(skb, offsetof(struct qca_dump_hdr, data0));
> >
> >               usb_disable_autosuspend(udev);
> >               bt_dev_info(hdev, "%s memdump size(%u)\n",
> >                           (pkt_type == HCI_ACLDATA_PKT) ? "ACL" : "event",
> >                           dump_size);
> >       } else {
> > -             sk_ptr += offsetof(struct qca_dump_hdr, data);
> > -             sk_len -= offsetof(struct qca_dump_hdr, data);
> > +             skb_pull(skb, offsetof(struct qca_dump_hdr, data));
> >       }
> >
> >       if (!btdata->qca_dump.ram_dump_size) {
> > @@ -3050,7 +3044,6 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >               return ret;
> >       }
> >
> > -     skb_pull(skb, skb->len - sk_len);
> >       hci_devcd_append(hdev, skb);
> >       btdata->qca_dump.ram_dump_seqno++;
> >       if (seqno == QCA_LAST_SEQUENCE_NUM) {
> > @@ -3078,68 +3071,58 @@ static int handle_dump_pkt_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >   /* Return: true if the ACL packet is a dump packet, false otherwise. */
> >   static bool acl_pkt_is_dump_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >   {
> > -     u8 *sk_ptr;
> > -     unsigned int sk_len;
> > -
> >       struct hci_event_hdr *event_hdr;
> >       struct hci_acl_hdr *acl_hdr;
> >       struct qca_dump_hdr *dump_hdr;
> > +     struct sk_buff *clone = skb_clone(skb, GFP_ATOMIC);
> > +     bool is_dump = false;
> >
> > -     sk_ptr = skb->data;
> > -     sk_len = skb->len;
> > -
> > -     acl_hdr = hci_acl_hdr(skb);
> > -     if (le16_to_cpu(acl_hdr->handle) != QCA_MEMDUMP_ACL_HANDLE)
> > +     if (!clone)
> >               return false;
> >
> > -     sk_ptr += HCI_ACL_HDR_SIZE;
> > -     sk_len -= HCI_ACL_HDR_SIZE;
> > -     event_hdr = (struct hci_event_hdr *)sk_ptr;
> > -
> > -     if ((event_hdr->evt != HCI_VENDOR_PKT) ||
> > -         (event_hdr->plen != (sk_len - HCI_EVENT_HDR_SIZE)))
> > -             return false;
> > +     acl_hdr = skb_pull_data(clone, sizeof(*acl_hdr));
> > +     if (!acl_hdr || (le16_to_cpu(acl_hdr->handle) != QCA_MEMDUMP_ACL_HANDLE))
> > +             goto out;
> >
> > -     sk_ptr += HCI_EVENT_HDR_SIZE;
> > -     sk_len -= HCI_EVENT_HDR_SIZE;
> > +     event_hdr = skb_pull_data(clone, sizeof(*event_hdr));
> > +     if (!event_hdr || (event_hdr->evt != HCI_VENDOR_PKT))
> > +             goto out;
> >
> > -     dump_hdr = (struct qca_dump_hdr *)sk_ptr;
> > -     if ((sk_len < offsetof(struct qca_dump_hdr, data)) ||
> > -         (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
> > -         (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
> > -             return false;
> > +     dump_hdr = skb_pull_data(clone, sizeof(*dump_hdr));
> > +     if (!dump_hdr || (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
> > +        (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
> > +             goto out;
> >
> > -     return true;
> > +     is_dump = true;
> > +out:
> > +     consume_skb(clone);
> > +     return is_dump;
> >   }
> >
> >   /* Return: true if the event packet is a dump packet, false otherwise. */
> >   static bool evt_pkt_is_dump_qca(struct hci_dev *hdev, struct sk_buff *skb)
> >   {
> > -     u8 *sk_ptr;
> > -     unsigned int sk_len;
> > -
> >       struct hci_event_hdr *event_hdr;
> >       struct qca_dump_hdr *dump_hdr;
> > +     struct sk_buff *clone = skb_clone(skb, GFP_ATOMIC);
> > +     bool is_dump = false;
> >
> > -     sk_ptr = skb->data;
> > -     sk_len = skb->len;
> > -
> > -     event_hdr = hci_event_hdr(skb);
> > -
> > -     if ((event_hdr->evt != HCI_VENDOR_PKT)
> > -         || (event_hdr->plen != (sk_len - HCI_EVENT_HDR_SIZE)))
> > +     if (!clone)
> >               return false;
> >
> > -     sk_ptr += HCI_EVENT_HDR_SIZE;
> > -     sk_len -= HCI_EVENT_HDR_SIZE;
> > +     event_hdr = skb_pull_data(clone, sizeof(*event_hdr));
> > +     if (!event_hdr || (event_hdr->evt != HCI_VENDOR_PKT))
> > +             goto out;
> >
> > -     dump_hdr = (struct qca_dump_hdr *)sk_ptr;
> > -     if ((sk_len < offsetof(struct qca_dump_hdr, data)) ||
> > -         (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
> > -         (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
> > -             return false;
> > +     dump_hdr = skb_pull_data(clone, sizeof(*dump_hdr));
> > +     if (!dump_hdr || (dump_hdr->vse_class != QCA_MEMDUMP_VSE_CLASS) ||
> > +        (dump_hdr->msg_type != QCA_MEMDUMP_MSG_TYPE))
> > +             goto out;
> >
> > -     return true;
> > +     is_dump = true;
> > +out:
> > +     consume_skb(clone);
> > +     return is_dump;
> >   }
> >
> >   static int btusb_recv_acl_qca(struct hci_dev *hdev, struct sk_buff *skb)
>