* [RFC] Bluetooth: L2CAP: Fix to handling fragmented header
@ 2020-07-28 7:04 Luiz Augusto von Dentz
2020-07-28 7:22 ` Marcel Holtmann
0 siblings, 1 reply; 3+ messages in thread
From: Luiz Augusto von Dentz @ 2020-07-28 7:04 UTC (permalink / raw)
To: linux-bluetooth
From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Bluetooth Core Specification v5.2, Vol. 3, Part A, section 1.4, table
1.1:
'Start Fragments always either begin with the first octet of the Basic
L2CAP header of a PDU or they have a length of zero (see [Vol 2] Part
B, Section 6.6.2).'
This text has been changed recently as it previously stated:
'Start Fragments always begin with the Basic L2CAP header of a PDU.'
Apparently this was changed by the following errata:
https://www.bluetooth.org/tse/errata_view.cfm?errata_id=10216
In past this has not been a problem but it seems new controllers are
apparently doing it as it has been reported in Zephyr:
https://github.com/zephyrproject-rtos/zephyr/issues/26900
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
net/bluetooth/l2cap_core.c | 104 +++++++++++++++++++++++++++++--------
1 file changed, 83 insertions(+), 21 deletions(-)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index ade83e224567..193bea314222 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -8269,6 +8269,63 @@ static void l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
mutex_unlock(&conn->chan_lock);
}
+/* Append fragment into frame respecting the maximum len of rx_skb */
+static int l2cap_recv_frag(struct l2cap_conn *conn, struct sk_buff *skb,
+ u16 len)
+{
+ if (!conn->rx_skb) {
+ /* Allocate skb for the complete frame (with header) */
+ conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL);
+ if (!conn->rx_skb)
+ return -ENOMEM;
+ /* Init rx_len */
+ conn->rx_len = len;
+ }
+
+ /* Copy as much as the rx_skb can hold */
+ len = min_t(u16, len, skb->len);
+ skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, len), len);
+ skb_pull(skb, len);
+ conn->rx_len -= len;
+
+ return len;
+}
+
+static int l2cap_recv_header(struct l2cap_conn *conn, struct sk_buff *skb)
+{
+ struct l2cap_hdr *hdr;
+ struct sk_buff *rx_skb;
+ int len;
+
+ /* Append just enough to complete the header */
+ len = l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE - conn->rx_skb->len);
+
+ /* If header could not be read just continue */
+ if (len < 0 || conn->rx_skb->len < L2CAP_HDR_SIZE)
+ return len;
+
+ rx_skb = conn->rx_skb;
+ conn->rx_skb = NULL;
+
+ hdr = (struct l2cap_hdr *) rx_skb->data;
+
+ /* Append existing rx_skb as that allocates only enough for the
+ * headers.
+ */
+ len = l2cap_recv_frag(conn, rx_skb,
+ __le16_to_cpu(hdr->len) + L2CAP_HDR_SIZE);
+ kfree_skb(rx_skb);
+
+ return len;
+}
+
+static void l2cap_recv_reset(struct l2cap_conn *conn)
+{
+ kfree_skb(conn->rx_skb);
+ conn->rx_skb = NULL;
+ conn->rx_len = 0;
+}
+
void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
{
struct l2cap_conn *conn = hcon->l2cap_data;
@@ -8291,19 +8348,19 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
case ACL_START:
case ACL_START_NO_FLUSH:
case ACL_COMPLETE:
- if (conn->rx_len) {
+ if (conn->rx_skb) {
BT_ERR("Unexpected start frame (len %d)", skb->len);
- kfree_skb(conn->rx_skb);
- conn->rx_skb = NULL;
- conn->rx_len = 0;
+ l2cap_recv_reset(conn);
l2cap_conn_unreliable(conn, ECOMM);
}
- /* Start fragment always begin with Basic L2CAP header */
+ /* Start fragment may not contain the L2CAP header so just
+ * copy the initial byte when that happens.
+ */
if (skb->len < L2CAP_HDR_SIZE) {
- BT_ERR("Frame is too short (len %d)", skb->len);
- l2cap_conn_unreliable(conn, ECOMM);
- goto drop;
+ if (l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE) < 0)
+ goto drop;
+ return;
}
hdr = (struct l2cap_hdr *) skb->data;
@@ -8324,38 +8381,43 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
goto drop;
}
- /* Allocate skb for the complete frame (with header) */
- conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL);
- if (!conn->rx_skb)
+ /* Append fragment into frame (with header) */
+ if (l2cap_recv_frag(conn, skb, len) < 0)
goto drop;
- skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb->len),
- skb->len);
- conn->rx_len = len - skb->len;
break;
case ACL_CONT:
BT_DBG("Cont: frag len %d (expecting %d)", skb->len, conn->rx_len);
- if (!conn->rx_len) {
+ if (!conn->rx_skb) {
BT_ERR("Unexpected continuation frame (len %d)", skb->len);
l2cap_conn_unreliable(conn, ECOMM);
goto drop;
}
+ /* Complete the L2CAP header if it has not been read */
+ if (conn->rx_skb->len < L2CAP_HDR_SIZE) {
+ if (l2cap_recv_header(conn, skb) < 0) {
+ l2cap_conn_unreliable(conn, ECOMM);
+ goto drop;
+ }
+
+ /* Header still could not be read just continue */
+ if (conn->rx_skb->len < L2CAP_HDR_SIZE)
+ return;
+ }
+
if (skb->len > conn->rx_len) {
BT_ERR("Fragment is too long (len %d, expected %d)",
skb->len, conn->rx_len);
- kfree_skb(conn->rx_skb);
- conn->rx_skb = NULL;
- conn->rx_len = 0;
+ l2cap_recv_reset(conn);
l2cap_conn_unreliable(conn, ECOMM);
goto drop;
}
- skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb->len),
- skb->len);
- conn->rx_len -= skb->len;
+ /* Append fragment into frame (with header) */
+ l2cap_recv_frag(conn, skb, skb->len);
if (!conn->rx_len) {
/* Complete frame received. l2cap_recv_frame
--
2.26.2
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [RFC] Bluetooth: L2CAP: Fix to handling fragmented header
2020-07-28 7:04 [RFC] Bluetooth: L2CAP: Fix to handling fragmented header Luiz Augusto von Dentz
@ 2020-07-28 7:22 ` Marcel Holtmann
2020-07-28 16:39 ` Luiz Augusto von Dentz
0 siblings, 1 reply; 3+ messages in thread
From: Marcel Holtmann @ 2020-07-28 7:22 UTC (permalink / raw)
To: Luiz Augusto von Dentz; +Cc: linux-bluetooth
Hi Luiz,
> Bluetooth Core Specification v5.2, Vol. 3, Part A, section 1.4, table
> 1.1:
>
> 'Start Fragments always either begin with the first octet of the Basic
> L2CAP header of a PDU or they have a length of zero (see [Vol 2] Part
> B, Section 6.6.2).'
>
> This text has been changed recently as it previously stated:
>
> 'Start Fragments always begin with the Basic L2CAP header of a PDU.'
>
> Apparently this was changed by the following errata:
>
> https://www.bluetooth.org/tse/errata_view.cfm?errata_id=10216
>
> In past this has not been a problem but it seems new controllers are
> apparently doing it as it has been reported in Zephyr:
>
> https://github.com/zephyrproject-rtos/zephyr/issues/26900
>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> ---
> net/bluetooth/l2cap_core.c | 104 +++++++++++++++++++++++++++++--------
> 1 file changed, 83 insertions(+), 21 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index ade83e224567..193bea314222 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -8269,6 +8269,63 @@ static void l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
> mutex_unlock(&conn->chan_lock);
> }
>
> +/* Append fragment into frame respecting the maximum len of rx_skb */
> +static int l2cap_recv_frag(struct l2cap_conn *conn, struct sk_buff *skb,
> + u16 len)
> +{
> + if (!conn->rx_skb) {
> + /* Allocate skb for the complete frame (with header) */
> + conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL);
> + if (!conn->rx_skb)
> + return -ENOMEM;
> + /* Init rx_len */
> + conn->rx_len = len;
> + }
> +
> + /* Copy as much as the rx_skb can hold */
> + len = min_t(u16, len, skb->len);
> + skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, len), len);
> + skb_pull(skb, len);
> + conn->rx_len -= len;
> +
> + return len;
> +}
> +
> +static int l2cap_recv_header(struct l2cap_conn *conn, struct sk_buff *skb)
> +{
> + struct l2cap_hdr *hdr;
> + struct sk_buff *rx_skb;
> + int len;
> +
> + /* Append just enough to complete the header */
> + len = l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE - conn->rx_skb->len);
> +
> + /* If header could not be read just continue */
> + if (len < 0 || conn->rx_skb->len < L2CAP_HDR_SIZE)
> + return len;
> +
> + rx_skb = conn->rx_skb;
> + conn->rx_skb = NULL;
> +
> + hdr = (struct l2cap_hdr *) rx_skb->data;
so I think it is pointless to insist on getting the complete header. We really just need the first 2 octets.
struct l2cap_hdr {
__le16 len;
__le16 cid;
} __packed;
Once we have received at least 2 octets, we can get_unaligned_le16(rx_skb->data) and then just continue.
Regards
Marcel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC] Bluetooth: L2CAP: Fix to handling fragmented header
2020-07-28 7:22 ` Marcel Holtmann
@ 2020-07-28 16:39 ` Luiz Augusto von Dentz
0 siblings, 0 replies; 3+ messages in thread
From: Luiz Augusto von Dentz @ 2020-07-28 16:39 UTC (permalink / raw)
To: Marcel Holtmann; +Cc: linux-bluetooth
Hi Marcel,
On Tue, Jul 28, 2020 at 12:22 AM Marcel Holtmann <marcel@holtmann.org> wrote:
>
> Hi Luiz,
>
> > Bluetooth Core Specification v5.2, Vol. 3, Part A, section 1.4, table
> > 1.1:
> >
> > 'Start Fragments always either begin with the first octet of the Basic
> > L2CAP header of a PDU or they have a length of zero (see [Vol 2] Part
> > B, Section 6.6.2).'
> >
> > This text has been changed recently as it previously stated:
> >
> > 'Start Fragments always begin with the Basic L2CAP header of a PDU.'
> >
> > Apparently this was changed by the following errata:
> >
> > https://www.bluetooth.org/tse/errata_view.cfm?errata_id=10216
> >
> > In past this has not been a problem but it seems new controllers are
> > apparently doing it as it has been reported in Zephyr:
> >
> > https://github.com/zephyrproject-rtos/zephyr/issues/26900
> >
> > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> > ---
> > net/bluetooth/l2cap_core.c | 104 +++++++++++++++++++++++++++++--------
> > 1 file changed, 83 insertions(+), 21 deletions(-)
> >
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index ade83e224567..193bea314222 100644
> > --- a/net/bluetooth/l2cap_core.c
> > +++ b/net/bluetooth/l2cap_core.c
> > @@ -8269,6 +8269,63 @@ static void l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt)
> > mutex_unlock(&conn->chan_lock);
> > }
> >
> > +/* Append fragment into frame respecting the maximum len of rx_skb */
> > +static int l2cap_recv_frag(struct l2cap_conn *conn, struct sk_buff *skb,
> > + u16 len)
> > +{
> > + if (!conn->rx_skb) {
> > + /* Allocate skb for the complete frame (with header) */
> > + conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL);
> > + if (!conn->rx_skb)
> > + return -ENOMEM;
> > + /* Init rx_len */
> > + conn->rx_len = len;
> > + }
> > +
> > + /* Copy as much as the rx_skb can hold */
> > + len = min_t(u16, len, skb->len);
> > + skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, len), len);
> > + skb_pull(skb, len);
> > + conn->rx_len -= len;
> > +
> > + return len;
> > +}
> > +
> > +static int l2cap_recv_header(struct l2cap_conn *conn, struct sk_buff *skb)
> > +{
> > + struct l2cap_hdr *hdr;
> > + struct sk_buff *rx_skb;
> > + int len;
> > +
> > + /* Append just enough to complete the header */
> > + len = l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE - conn->rx_skb->len);
> > +
> > + /* If header could not be read just continue */
> > + if (len < 0 || conn->rx_skb->len < L2CAP_HDR_SIZE)
> > + return len;
> > +
> > + rx_skb = conn->rx_skb;
> > + conn->rx_skb = NULL;
> > +
> > + hdr = (struct l2cap_hdr *) rx_skb->data;
>
> so I think it is pointless to insist on getting the complete header. We really just need the first 2 octets.
>
> struct l2cap_hdr {
> __le16 len;
> __le16 cid;
> } __packed;
Indeed, I've totally forgotten about the cid so I will change this to
not use L2CAP_HDR_SIZE but 2 instead.
> Once we have received at least 2 octets, we can get_unaligned_le16(rx_skb->data) and then just continue.
Sure, I was trying to figure out if there is any way to grow the the
rx_skb since I will be just allocating 2 bytes for it if the header is
not available, we could perhaps take a different approach and always
allocate based on the conn->mtu that way we don't have to wait the
length to received to allocate a second skb and copy over the length
into it, obviously that would only be done if length was fragmented.
> Regards
>
> Marcel
>
--
Luiz Augusto von Dentz
^ permalink raw reply [flat|nested] 3+ messages in thread
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