linux-kernel - [PATCH] phy: renesas: rcar-gen3-usb2: Fix sysfs interface of "role"

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Date:   Wed, 31 Jul 2019 18:01:29 +0900
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     kishon@...com
Cc:     pavel@...x.de, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, stable@...r.kernel.org,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Subject: [PATCH] phy: renesas: rcar-gen3-usb2: Fix sysfs interface of "role"

Since the role_store() uses strncmp(), it's possible to refer
out-of-memory if the sysfs data size is smaller than strlen("host").
This patch fixes it by using sysfs_streq() instead of strncmp().

Reported-by: Pavel Machek <pavel@...x.de>
Fixes: 9bb86777fb71 ("phy: rcar-gen3-usb2: add sysfs for usb role swap")
Cc: <stable@...r.kernel.org> # v4.10+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
---
 Just a record. The role_store() doesn't need to check the count because
 the sysfs_streq() checks the first argument is NULL or not.

 On "if (sysfs_streq(buf, "host"))"
  Example 1: echo ho > role
  --> In this case, the count is 3 and the buf has "ho" + NULL.
      So, the third character differs between NULL and 's'.

  Example 2: echo host-is-not-used > role
  --> In this case, the count is 17 and the buf has "host-is-not-used" + NULL.
      So, the fifth character differs between '-' and NULL.

 drivers/phy/renesas/phy-rcar-gen3-usb2.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/phy/renesas/phy-rcar-gen3-usb2.c b/drivers/phy/renesas/phy-rcar-gen3-usb2.c
index 1322185..cc18970 100644
--- a/drivers/phy/renesas/phy-rcar-gen3-usb2.c
+++ b/drivers/phy/renesas/phy-rcar-gen3-usb2.c
@@ -20,6 +20,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/regulator/consumer.h>
+#include <linux/string.h>
 #include <linux/usb/of.h>
 #include <linux/workqueue.h>
 
@@ -317,9 +318,9 @@ static ssize_t role_store(struct device *dev, struct device_attribute *attr,
 	if (!ch->is_otg_channel || !rcar_gen3_is_any_rphy_initialized(ch))
 		return -EIO;
 
-	if (!strncmp(buf, "host", strlen("host")))
+	if (sysfs_streq(buf, "host"))
 		new_mode = PHY_MODE_USB_HOST;
-	else if (!strncmp(buf, "peripheral", strlen("peripheral")))
+	else if (sysfs_streq(buf, "peripheral"))
 		new_mode = PHY_MODE_USB_DEVICE;
 	else
 		return -EINVAL;
-- 
2.7.4