linux-kernel - [PATCH] Bluetooth: RFCOMM: Use skb

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Date:   Wed,  8 Jun 2022 15:51:06 +0200
From:   Soenke Huster <soenke.huster@...oes.de>
To:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Soenke Huster <soenke.huster@...oes.de>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Bluetooth: RFCOMM: Use skb_trim to trim checksum

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@...oes.de>
---
 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