i2c: dev: zero out array used for i2c reads from userspace

commit 86ff25ed6cd8240d18df58930bd8848b19fce308 upstream.

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@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 1d10ee86299d831f3c4633022c554aa678b0cdcf..57aece80984166a016db2506b974db6eab9aff8c 100644 (file)
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -149,7 +149,7 @@ 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;
 
@@ -158,7 +158,8 @@ 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;
 }