[PATCH] Bluetooth: check L2CAP length in first ACL fragment

[Emeltchenko Andrei <Andrei.Emeltchenko.news@gmail.com>]

From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>

Current Bluetooth code assembles fragments of big L2CAP packets
in l2cap_recv_acldata and then checks allowed L2CAP size in
assembled L2CAP packet (pi->imtu < skb->len).

The patch moves allowed L2CAP size check to the early stage when
we receive the first fragment of L2CAP packet. First fragment has
already L2CAP header including length.

Trace below is received when using stress tools sending big
fragmented L2CAP packets.
...
[ 1712.798492] swapper: page allocation failure. order:4, mode:0x4020
[ 1712.804809] [<c0031870>] (unwind_backtrace+0x0/0xdc) from [<c00a1f70>]
(__alloc_pages_nodemask+0x4)
[ 1712.814666] [<c00a1f70>] (__alloc_pages_nodemask+0x47c/0x4d4) from
[<c00a1fd8>] (__get_free_pages+)
[ 1712.824645] [<c00a1fd8>] (__get_free_pages+0x10/0x3c) from [<c026eb5c>]
(__alloc_skb+0x4c/0xfc)
[ 1712.833465] [<c026eb5c>] (__alloc_skb+0x4c/0xfc) from [<bf28c738>]
(l2cap_recv_acldata+0xf0/0x1f8 )
[ 1712.843322] [<bf28c738>] (l2cap_recv_acldata+0xf0/0x1f8 [l2cap]) from
[<bf0094ac>] (hci_rx_task+0x)
...

After applying patch dmesg looks like:
...
l2cap_recv_acldata: Frame exceeding recv MTU (len 64182, MTU 1013)
l2cap_recv_acldata: Unexpected continuation frame (len 34)
...

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
---
 net/bluetooth/l2cap.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 9fad312..21824d7 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -4654,6 +4654,8 @@ static int l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 fl
 
 	if (flags & ACL_START) {
 		struct l2cap_hdr *hdr;
+		struct sock *sk;
+		u16 cid;
 		int len;
 
 		if (conn->rx_len) {
@@ -4672,6 +4674,7 @@ static int l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 fl
 
 		hdr = (struct l2cap_hdr *) skb->data;
 		len = __le16_to_cpu(hdr->len) + L2CAP_HDR_SIZE;
+		cid = __le16_to_cpu(hdr->cid);
 
 		if (len == skb->len) {
 			/* Complete frame received */
@@ -4688,6 +4691,14 @@ static int l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 fl
 			goto drop;
 		}
 
+		sk = l2cap_get_chan_by_scid(&conn->chan_list, cid);
+		if (l2cap_pi(sk)->imtu < len) {
+			BT_ERR("Frame exceeding recv MTU (len %d, MTU %d)",
+					len, l2cap_pi(sk)->imtu);
+			conn->rx_len = 0; /* needed? */
+			goto drop;
+		}
+
 		/* Allocate skb for the complete frame (with header) */
 		conn->rx_skb = bt_skb_alloc(len, GFP_ATOMIC);
 		if (!conn->rx_skb)
-- 
1.7.0.4