linux-kernel - [PATCH 5.9 134/757] media: uvcvideo: Silence shift-out-of-bounds warning

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Date:   Tue, 27 Oct 2020 14:46:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.9 134/757] media: uvcvideo: Silence shift-out-of-bounds warning

From: Laurent Pinchart <laurent.pinchart@...asonboard.com>

[ Upstream commit 171994e498a0426cbe17f874c5c6af3c0af45200 ]

UBSAN reports a shift-out-of-bounds warning in uvc_get_le_value(). The
report is correct, but the issue should be harmless as the computed
value isn't used when the shift is negative. This may however cause
incorrect behaviour if a negative shift could generate adverse side
effects (such as a trap on some architectures for instance).

Regardless of whether that may happen or not, silence the warning as a
full WARN backtrace isn't nice.

Reported-by: Bart Van Assche <bvanassche@....org>
Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Reviewed-by: Bart Van Assche <bvanassche@....org>
Tested-by: Bart Van Assche <bvanassche@....org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index e399b9fad7574..a30a8a731eda8 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -773,12 +773,16 @@ static s32 uvc_get_le_value(struct uvc_control_mapping *mapping,
 	offset &= 7;
 	mask = ((1LL << bits) - 1) << offset;
 
-	for (; bits > 0; data++) {
+	while (1) {
 		u8 byte = *data & mask;
 		value |= offset > 0 ? (byte >> offset) : (byte << (-offset));
 		bits -= 8 - (offset > 0 ? offset : 0);
+		if (bits <= 0)
+			break;
+
 		offset -= 8;
 		mask = (1 << bits) - 1;
+		data++;
 	}
 
 	/* Sign-extend the value if needed. */
-- 
2.25.1