Re: [syzbot] [PATCH] usbhid: fix array-index-out-of-bounds in usbhid_parse UBSAN warning

[syzbot <syzbot+c52569baf0c843f35495@syzkaller.appspotmail.com>]

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Subject: [PATCH] usbhid: fix array-index-out-of-bounds in usbhid_parse UBSAN warning
Author: tintinm2017@gmail.com

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Look at the bug https://syzkaller.appspot.com/bug?extid=c52569baf0c843f35495 reported by syzbot. Tested a patch through syzbot, which gives an error. 
Requesting help from the maintainers to understand what is really going wrong in the code. 

Based on my understanding, I believe the value of the number of descriptors is calculated incorrectly before the for loop.

Signed-off-by: Attreyee Mukherjee <tintinm2017@gmail.com>
---
 drivers/hid/usbhid/hid-core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index a90ed2ceae84..582ddbef448f 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -1021,6 +1021,8 @@ static int usbhid_parse(struct hid_device *hid)
 	       (hdesc->bLength - offset) / sizeof(struct hid_class_descriptor));
 
 	for (n = 0; n < num_descriptors; n++)
+		if (n >= ARRAY_SIZE(hdesc->desc))
+			break;
 		if (hdesc->desc[n].bDescriptorType == HID_DT_REPORT)
 			rsize = le16_to_cpu(hdesc->desc[n].wDescriptorLength);
 
-- 
2.34.1