linux-kernel - [PATCH v3] usb: gadget: ether: Fix MAC address parsing

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Date:	Thu, 14 May 2015 18:50:54 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	balbi@...com, gregkh@...uxfoundation.org
Cc:	k.opasiak@...sung.com, andrzej.p@...sung.com,
	m.szyprowski@...sung.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, stefan@...er.ch
Subject: [PATCH v3] usb: gadget: ether: Fix MAC address parsing

MAC addresses can be written without leading zeros. A popular
example is libc's ether_ntoa_r function which creates such
MAC addresses.

Example:
00:14:3d:0f:ff:fe can be written as 0:14:3d:f:ff:fe

The function get_ether_addr potentially also parsed past the
end of the user provided string. Use the opportunity and fix
the function to never parse beyond the end of the string while
allowing MAC addresses with and without leading zeros. Also
corner cases such as 00:14:3d:0f:ff:0 + new-line character
are parsed correctly.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
Changes since v2:
- Fix parameter description
- Return with error if invalid charaters are part of the string

 drivers/usb/gadget/function/u_ether.c | 70 ++++++++++++++++++++++++++++-------
 1 file changed, 56 insertions(+), 14 deletions(-)

diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
index f1fd777..c71ab21 100644
--- a/drivers/usb/gadget/function/u_ether.c
+++ b/drivers/usb/gadget/function/u_ether.c
@@ -703,25 +703,62 @@ static int eth_stop(struct net_device *net)
 
 /*-------------------------------------------------------------------------*/
 
+/**
+ * get_ether_addr - parse ethernet address from string
+ * @str: string to parse
+ * @dev_addr: a buffer in which the parsed ethernet address will be
+ *      written
+ *
+ * Several common formats are supported:
+ * 1) 00:14:3d:0f:ff:fe (no skipped 0, semicolons)
+ * 2) 00.14.3d.0f.ff.fe (no skipped 0, dots)
+ * 3) 00143d0ffffe (no skipped 0, no separator)
+ * 4) 0:14:3d:f:ff:fe (skipped leading 0, semicolons)
+ * 5) 0.14.3d.f.ff.fe (skipped leading 0, dots)
+ *
+ * The function will not cross the end of the provided string even
+ * when the string has the wrong format.
+ *
+ * Returns 0 on success, or -EINVAL on error
+ */
 static int get_ether_addr(const char *str, u8 *dev_addr)
 {
-	if (str) {
-		unsigned	i;
+	int num, i;
 
-		for (i = 0; i < 6; i++) {
-			unsigned char num;
+	for (i = 0; i < ETH_ALEN; i++) {
+		int j = 0;
 
-			if ((*str == '.') || (*str == ':'))
+		dev_addr[i] = 0;
+		while (*str) {
+			char c = *str;
+
+			if (c == '.' || c == ':') {
 				str++;
-			num = hex_to_bin(*str++) << 4;
-			num |= hex_to_bin(*str++);
-			dev_addr [i] = num;
+				break;
+			}
+
+			if (j >= 2)
+				break;
+
+			/* Ignore newline character, e.g. when using echo */
+			if (c == '\n')
+				continue;
+
+			num = hex_to_bin(c);
+			if (num < 0)
+				return num;
+
+			dev_addr[i] <<= 4;
+			dev_addr[i] |= num;
+			j++;
+			str++;
 		}
-		if (is_valid_ether_addr(dev_addr))
-			return 0;
 	}
-	eth_random_addr(dev_addr);
-	return 1;
+
+	if (!is_valid_ether_addr(dev_addr))
+		return -EINVAL;
+
+	return 0;
 }
 
 static int get_ether_addr_str(u8 dev_addr[ETH_ALEN], char *str, int len)
@@ -786,12 +823,17 @@ struct eth_dev *gether_setup_name(struct usb_gadget *g,
 	dev->qmult = qmult;
 	snprintf(net->name, sizeof(net->name), "%s%%d", netname);
 
-	if (get_ether_addr(dev_addr, net->dev_addr))
+	if (get_ether_addr(dev_addr, net->dev_addr)) {
+		eth_random_addr(net->dev_addr);
 		dev_warn(&g->dev,
 			"using random %s ethernet address\n", "self");
-	if (get_ether_addr(host_addr, dev->host_mac))
+	}
+
+	if (get_ether_addr(host_addr, dev->host_mac)) {
+		eth_random_addr(dev->host_mac);
 		dev_warn(&g->dev,
 			"using random %s ethernet address\n", "host");
+	}
 
 	if (ethaddr)
 		memcpy(ethaddr, dev->host_mac, ETH_ALEN);
-- 
2.4.0

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