[PATCH] Bluetooth: L2CAP: don't check for out-of-bounds value

From: Simon Horman <horms@kernel.org>
To: Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: Dan Carpenter <dan.carpenter@linaro.org>,
	linux-bluetooth@vger.kernel.org, Simon Horman <horms@kernel.org>
Subject: [PATCH] Bluetooth: L2CAP: don't check for out-of-bounds value
Date: Fri, 26 May 2023 16:16:54 +0200	[thread overview]
Message-ID: <20230526-l2cap-16bit-v1-1-2cfb83dd28ee@kernel.org> (raw)

In l2cap_connect(), scid is an unsigned 16bit variable. Thus, it's
maximum value is L2CAP_CID_DYN_END (0xffff) and there is no need
to check for this value being exceeded.

Flagged by Smatch as:

  .../l2cap_core.c:4165 l2cap_connect() warn: impossible condition '(scid > 65535) => (0-u16max > u16max)'

Signed-off-by: Simon Horman <horms@kernel.org>
---
 net/bluetooth/l2cap_core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index ae397c6819d9..a5d85a5f5930 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4161,8 +4161,12 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
 
 	result = L2CAP_CR_NO_MEM;
 
-	/* Check for valid dynamic CID range (as per Erratum 3253) */
-	if (scid < L2CAP_CID_DYN_START || scid > L2CAP_CID_DYN_END) {
+	/* Check for valid dynamic CID range (as per Erratum 3253).
+	 * As scid is an unsigned 16bit variable it's maximum
+	 * value is L2CAP_CID_DYN_END (0xffff): there is no need to check
+	 * if scid exceeds that value here.
+	 */
+	if (scid < L2CAP_CID_DYN_START) {
 		result = L2CAP_CR_INVALID_SCID;
 		goto response;
 	}

