[PATCH] usb: gadget: configfs: Fix OOB read on empty string write

[Xinyu Liu]

When writing an empty string to either 'qw_sign' or 'landingPage'
sysfs attributes, the store functions attempt to access page[l - 1]
before validating that the length 'l' is greater than zero.

This patch fixes the vulnerability by adding a check at the beginning
of os_desc_qw_sign_store() and webusb_landingPage_store() to handle
the zero-length input case gracefully by returning immediately.

Signed-off-by: Xinyu Liu <katieeliu@xxxxxxxxxxx>
---
 drivers/usb/gadget/configfs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index fba2a56dae97..1bb32d6be9b3 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -1064,7 +1064,8 @@ static ssize_t webusb_landingPage_store(struct config_item *item, const char *pa
 	struct gadget_info *gi = webusb_item_to_gadget_info(item);
 	unsigned int bytes_to_strip = 0;
 	int l = len;
-
+	if (!len)
+		return len;
 	if (page[l - 1] == '\n') {
 		--l;
 		++bytes_to_strip;
@@ -1187,7 +1188,8 @@ static ssize_t os_desc_qw_sign_store(struct config_item *item, const char *page,
 {
 	struct gadget_info *gi = os_desc_item_to_gadget_info(item);
 	int res, l;
-
+	if (!len)
+		return len;
 	l = min_t(int, len, OS_STRING_QW_SIGN_LEN >> 1);
 	if (page[l - 1] == '\n')
 		--l;
-- 
2.39.5 (Apple Git-154)