[PATCH] Bluetooth: RFCOMM: Use skb_trim to trim checksum

[Soenke Huster <soenke.huster@xxxxxxxxx>]

Use the skb helper instead of direct manipulation. This fixes the
following page fault, when connecting my Android phone:

    BUG: unable to handle page fault for address: ffffed1021de29ff
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    RIP: 0010:rfcomm_run+0x831/0x4040 (net/bluetooth/rfcomm/core.c:1751)

Signed-off-by: Soenke Huster <soenke.huster@xxxxxxxxx>
---
 net/bluetooth/rfcomm/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 7324764384b6..7360e905d045 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1747,8 +1747,8 @@ static struct rfcomm_session *rfcomm_recv_frame(struct rfcomm_session *s,
 	type = __get_type(hdr->ctrl);
 
 	/* Trim FCS */
-	skb->len--; skb->tail--;
-	fcs = *(u8 *)skb_tail_pointer(skb);
+	skb_trim(skb, skb->len - 1);
+	fcs = *(skb->data + skb->len);
 
 	if (__check_fcs(skb->data, type, fcs)) {
 		BT_ERR("bad checksum in packet");
-- 
2.36.1