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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Ben Hutchings <ben.hutchings@codethink.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 3.18 04/13] USB: yurex: Check for truncation in
 yurex_read()
Thread-Topic: [PATCH AUTOSEL 3.18 04/13] USB: yurex: Check for truncation in
 yurex_read()
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Date:   Mon, 1 Oct 2018 00:41:46 +0000
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From: Ben Hutchings <ben.hutchings@codethink.co.uk>

[ Upstream commit 14427b86837a4baf1c121934c6599bdb67dfa9fc ]

snprintf() always returns the full length of the string it could have
printed, even if it was truncated because the buffer was too small.
So in case the counter value is truncated, we will over-read from
in_buffer and over-write to the caller's buffer.

I don't think it's actually possible for this to happen, but in case
truncation occurs, WARN and return -EIO.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 drivers/usb/misc/yurex.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 83eaccfa9ee5..fbcb1cd4c118 100644
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -430,6 +430,9 @@ static ssize_t yurex_read(struct file *file, char *buff=
er, size_t count, loff_t
 	spin_unlock_irqrestore(&dev->lock, flags);
 	mutex_unlock(&dev->io_mutex);
=20
+	if (WARN_ON_ONCE(len >=3D sizeof(in_buffer)))
+		return -EIO;
+
 	return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);
 }
=20
--=20
2.17.1