linux-kernel - [PATCH v2] i2c: dev: zero out array used for i2c reads from userspace

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Date:   Thu, 29 Jul 2021 16:35:32 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        stable <stable@...r.kernel.org>
Subject: [PATCH v2] i2c: dev: zero out array used for i2c reads from userspace

If an i2c driver happens to not provide the full amount of data that a
user asks for, it is possible that some uninitialized data could be sent
to userspace.  While all in-kernel drivers look to be safe, just be sure
by initializing the buffer to zero before it is passed to the i2c driver
so that any future drivers will not have this issue.

Also properly copy the amount of data recvieved to the userspace buffer,
as pointed out by Dan Carpenter.

Reported-by: Eric Dumazet <edumazet@...gle.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
v2: Add copy_to_user() change as pointed out by Dan

 drivers/i2c/i2c-dev.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index cb64fe649390..77f576e51652 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -141,7 +141,7 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,
 	if (count > 8192)
 		count = 8192;
 
-	tmp = kmalloc(count, GFP_KERNEL);
+	tmp = kzalloc(count, GFP_KERNEL);
 	if (tmp == NULL)
 		return -ENOMEM;
 
@@ -150,7 +150,8 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,
 
 	ret = i2c_master_recv(client, tmp, count);
 	if (ret >= 0)
-		ret = copy_to_user(buf, tmp, count) ? -EFAULT : ret;
+		if (copy_to_user(buf, tmp, ret))
+			ret = -EFAULT;
 	kfree(tmp);
 	return ret;
 }
-- 
2.32.0