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From:   Anirudh Rayabharam <mail@anirudhrb.com>
To:     Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Anirudh Rayabharam <mail@anirudhrb.com>,
        syzbot+7c2bb71996f95a82524c@syzkaller.appspotmail.com,
        linux-usb@vger.kernel.org, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] usbhid: fix info leak in hid_submit_ctrl
Date:   Sun, 25 Apr 2021 23:03:53 +0530
Message-Id: <20210425173353.10231-1-mail@anirudhrb.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In hid_submit_ctrl(), the way of calculating the report length doesn't
take into account that report->size can be zero. When running the
syzkaller reproducer, a report of size 0 causes hid_submit_ctrl) to
calculate transfer_buffer_length as 16384. When this urb is passed to
the usb core layer, KMSAN reports an info leak of 16384 bytes.

To fix this, first modify hid_report_len() to account for the zero
report size case by using DIV_ROUND_UP for the division. Then, call it
from hid_submit_ctrl().

Reported-by: syzbot+7c2bb71996f95a82524c@syzkaller.appspotmail.com
Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
---
 drivers/hid/usbhid/hid-core.c | 2 +-
 include/linux/hid.h           | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index 86257ce6d619..4e9077363c96 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -374,7 +374,7 @@ static int hid_submit_ctrl(struct hid_device *hid)
 	raw_report = usbhid->ctrl[usbhid->ctrltail].raw_report;
 	dir = usbhid->ctrl[usbhid->ctrltail].dir;
 
-	len = ((report->size - 1) >> 3) + 1 + (report->id > 0);
+	len = hid_report_len(report);
 	if (dir == USB_DIR_OUT) {
 		usbhid->urbctrl->pipe = usb_sndctrlpipe(hid_to_usb_dev(hid), 0);
 		usbhid->urbctrl->transfer_buffer_length = len;
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 271021e20a3f..10e922cee4eb 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -1167,8 +1167,7 @@ static inline void hid_hw_wait(struct hid_device *hdev)
  */
 static inline u32 hid_report_len(struct hid_report *report)
 {
-	/* equivalent to DIV_ROUND_UP(report->size, 8) + !!(report->id > 0) */
-	return ((report->size - 1) >> 3) + 1 + (report->id > 0);
+	return DIV_ROUND_UP(report->size, 8) + (report->id > 0);
 }
 
 int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
-- 
2.26.2