NTB: ntb_tool: uninitialized heap data in tool_fn_write()

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2179137
Upstream Status: 45e1058b77feade4e36402828bfe3e0d3363177b

commit 45e1058b77feade4e36402828bfe3e0d3363177b
Author: Dan Carpenter <error27@gmail.com>
Date:   Wed Jul 20 21:28:18 2022 +0300

    NTB: ntb_tool: uninitialized heap data in tool_fn_write()

    The call to:

            ret = simple_write_to_buffer(buf, size, offp, ubuf, size);

    will return success if it is able to write even one byte to "buf".
    The value of "*offp" controls which byte.  This could result in
    reading uninitialized data when we do the sscanf() on the next line.

    This code is not really desigined to handle partial writes where
    *offp is non-zero and the "buf" is preserved and re-used between writes.
    Just ban partial writes and replace the simple_write_to_buffer() with
    copy_from_user().

    Fixes: 578b881ba9 ("NTB: Add tool test client")
    Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: Jon Mason <jdmason@kudzu.us>

Signed-off-by: Myron Stowe <mstowe@redhat.com>

drivers/ntb/test/ntb_tool.c

@@ -367,14 +367,16 @@ static ssize_t tool_fn_write(struct tool_ctx *tc,
 	u64 bits;
 	int n;
 
+	if (*offp)
+		return 0;
+
 	buf = kmalloc(size + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	ret = simple_write_to_buffer(buf, size, offp, ubuf, size);
-	if (ret < 0) {
+	if (copy_from_user(buf, ubuf, size)) {
 		kfree(buf);
-		return ret;
+		return -EFAULT;
 	}
 
 	buf[size] = 0;