linux-kernel - [PATCH] media: hdpvr: fix error value returns in hdpvr

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Message-Id: <20220614175002.120931-1-dossche.niels@gmail.com>
Date:   Tue, 14 Jun 2022 19:50:02 +0200
From:   Niels Dossche <dossche.niels@...il.com>
To:     linux-media@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Dongliang Mu <mudongliangabcd@...il.com>,
        Niels Dossche <dossche.niels@...il.com>
Subject: [PATCH] media: hdpvr: fix error value returns in hdpvr_read

Error return values are supposed to be negative in hdpvr_read. Most
error returns are currently handled via an unsigned integer "ret". When
setting a negative error value to "ret", the value actually becomes a
large positive value, because "ret" is unsigned. Later on, the "ret"
value is returned. But as ssize_t is a 64-bit signed number, the error
return value stays a large positive integer instead of a negative
integer. This can cause an error value to be interpreted as the read
size, which can cause a buffer overread for applications relying on the
returned size.

Fixes: 9aba42efe85b ("V4L/DVB (11096): V4L2 Driver for the Hauppauge HD PVR usb capture device")
Signed-off-by: Niels Dossche <dossche.niels@...il.com>
---

Note:
I found this issue using my own-developed static analysis tool to find
inconsistent error return values. As I do not have the necessary
hardware to test, I could not test this patch. I only compile-tested
this on x86-64. I found this issue on v5.19-rc2.
I manually verified the issue report by looking at the code.

 drivers/media/usb/hdpvr/hdpvr-video.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/hdpvr/hdpvr-video.c b/drivers/media/usb/hdpvr/hdpvr-video.c
index 60e57e0f1927..fd7d2a9d0449 100644
--- a/drivers/media/usb/hdpvr/hdpvr-video.c
+++ b/drivers/media/usb/hdpvr/hdpvr-video.c
@@ -409,7 +409,7 @@ static ssize_t hdpvr_read(struct file *file, char __user *buffer, size_t count,
 	struct hdpvr_device *dev = video_drvdata(file);
 	struct hdpvr_buffer *buf = NULL;
 	struct urb *urb;
-	unsigned int ret = 0;
+	int ret = 0;
 	int rem, cnt;

 	if (*pos)
-- 
2.36.1