linux-kernel - [PATCH 18/26] usb: gadget: legacy: remove using list iterator after loop body as a ptr

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Date:   Sun,  6 Mar 2022 18:50:26 +0100
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Greg Kroah-Hartman <greg@...ah.com>
Cc:     Jakob Koschel <jakobkoschel@...il.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Felipe Balbi <balbi@...nel.org>, Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Cristian Birsan <cristian.birsan@...rochip.com>,
        Al Cooper <alcooperx@...il.com>, Li Yang <leoyang.li@....com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michal Simek <michal.simek@...inx.com>,
        linux-usb@...r.kernel.org (open list:USB GADGET/PERIPHERAL SUBSYSTEM),
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: [PATCH 18/26] usb: gadget: legacy: remove using list iterator after loop body as a ptr

If the list does not contain the expected element, the value of
list_for_each_entry() iterator will not point to a valid structure.
To avoid type confusion in such case, the list iterator
scope will be limited to list_for_each_entry() loop.

In preparation to limiting scope of a list iterator to the list traversal
loop, use a dedicated pointer to point to the found element [1].
Determining if an element was found is then simply checking if
the pointer is != NULL instead of using the potentially bogus pointer.

Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 drivers/usb/gadget/legacy/hid.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/usb/gadget/legacy/hid.c b/drivers/usb/gadget/legacy/hid.c
index 3912cc805f3a..b7f1ff2ce951 100644
--- a/drivers/usb/gadget/legacy/hid.c
+++ b/drivers/usb/gadget/legacy/hid.c
@@ -134,7 +134,7 @@ static int hid_bind(struct usb_composite_dev *cdev)
 {
 	struct usb_gadget *gadget = cdev->gadget;
 	struct list_head *tmp;
-	struct hidg_func_node *n, *m;
+	struct hidg_func_node *n = NULL, *m, *tmp_n;
 	struct f_hid_opts *hid_opts;
 	int status, funcs = 0;
 
@@ -144,18 +144,19 @@ static int hid_bind(struct usb_composite_dev *cdev)
 	if (!funcs)
 		return -ENODEV;
 
-	list_for_each_entry(n, &hidg_func_list, node) {
-		n->fi = usb_get_function_instance("hid");
-		if (IS_ERR(n->fi)) {
-			status = PTR_ERR(n->fi);
+	list_for_each_entry(tmp_n, &hidg_func_list, node) {
+		tmp_n->fi = usb_get_function_instance("hid");
+		if (IS_ERR(tmp_n->fi)) {
+			status = PTR_ERR(tmp_n->fi);
+			n = tmp_n;
 			goto put;
 		}
-		hid_opts = container_of(n->fi, struct f_hid_opts, func_inst);
-		hid_opts->subclass = n->func->subclass;
-		hid_opts->protocol = n->func->protocol;
-		hid_opts->report_length = n->func->report_length;
-		hid_opts->report_desc_length = n->func->report_desc_length;
-		hid_opts->report_desc = n->func->report_desc;
+		hid_opts = container_of(tmp_n->fi, struct f_hid_opts, func_inst);
+		hid_opts->subclass = tmp_n->func->subclass;
+		hid_opts->protocol = tmp_n->func->protocol;
+		hid_opts->report_length = tmp_n->func->report_length;
+		hid_opts->report_desc_length = tmp_n->func->report_desc_length;
+		hid_opts->report_desc = tmp_n->func->report_desc;
 	}
 
 
-- 
2.25.1