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([187.13.206.89]) by smtp.gmail.com with ESMTPSA id ada2fe7eead31-79fb193e849sm78576137.8.2026.09.15.09.02.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 09:02:51 -0700 (PDT) From: Aldo Ariel Panzardo To: Luiz Augusto von Dentz Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Aldo Ariel Panzardo Subject: [PATCH] Bluetooth: L2CAP: validate frame length before control and FCS access Date: Tue, 15 Sep 2026 13:02:39 -0300 Message-ID: <20260915160239.3106697-1-qwe.aldo@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit l2cap_data_rcv() unpacks either a two-byte or four-byte control field without first ensuring that it is present. A short ERTM or streaming-mode frame can therefore cause an out-of-bounds read. There is a second short-frame case when CRC16 is enabled. After the control field is pulled, l2cap_check_fcs() subtracts two from skb->len without checking it. If fewer than two bytes remain, the subtraction wraps; skb_trim() leaves the buffer unchanged and the subsequent FCS load reads past the logical end of the frame. Validate that the frame contains both its control field and, when enabled, its FCS before either field is accessed. Fixes: 1c2acffb76d4 ("Bluetooth: Add initial support for ERTM packets transfers") Fixes: fcc203c30d72 ("Bluetooth: Add support for FCS option to L2CAP") Cc: stable@vger.kernel.org Signed-off-by: Aldo Ariel Panzardo --- net/bluetooth/l2cap_core.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 1156aba4e..40ebabe34 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -6683,9 +6683,17 @@ static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control, static int l2cap_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb) { struct l2cap_ctrl *control = &bt_cb(skb)->l2cap; - u16 len; + u16 len, min_len; u8 event; + min_len = test_bit(FLAG_EXT_CTRL, &chan->flags) ? + L2CAP_EXT_CTRL_SIZE : L2CAP_ENH_CTRL_SIZE; + if (chan->fcs == L2CAP_FCS_CRC16) + min_len += L2CAP_FCS_SIZE; + + if (skb->len < min_len) + goto drop; + __unpack_control(chan, skb); len = skb->len; -- 2.43.0