linux-kernel - [PATCH 4.4 45/68] platform/chrome: cros_ec_dev

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Date:	Mon,  8 Aug 2016 21:11:20 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Pengfei Wang <wpengfeinudt@...il.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Kees Cook <keescook@...omium.org>,
	Gwendal Grignou <gwendal@...omium.org>,
	Olof Johansson <olof@...om.net>
Subject: [PATCH 4.4 45/68] platform/chrome: cros_ec_dev - double fetch bug in ioctl

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@...cle.com>

commit 096cdc6f52225835ff503f987a0d68ef770bb78e upstream.

We verify "u_cmd.outsize" and "u_cmd.insize" but we need to make sure
that those values have not changed between the two copy_from_user()
calls.  Otherwise it could lead to a buffer overflow.

Additionally, cros_ec_cmd_xfer() can set s_cmd->insize to a lower value.
We should use the new smaller value so we don't copy too much data to
the user.

Reported-by: Pengfei Wang <wpengfeinudt@...il.com>
Fixes: a841178445bb ('mfd: cros_ec: Use a zero-length array for command data')
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Tested-by: Gwendal Grignou <gwendal@...omium.org>
Signed-off-by: Olof Johansson <olof@...om.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/platform/chrome/cros_ec_dev.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -147,13 +147,19 @@ static long ec_device_ioctl_xcmd(struct
 		goto exit;
 	}
 
+	if (u_cmd.outsize != s_cmd->outsize ||
+	    u_cmd.insize != s_cmd->insize) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
 	s_cmd->command += ec->cmd_offset;
 	ret = cros_ec_cmd_xfer(ec->ec_dev, s_cmd);
 	/* Only copy data to userland if data was received. */
 	if (ret < 0)
 		goto exit;
 
-	if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + u_cmd.insize))
+	if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + s_cmd->insize))
 		ret = -EFAULT;
 exit:
 	kfree(s_cmd);