NTB: ntb_tool: uninitialized heap data in tool_fn_write()

stable inclusion
from stable-v5.10.138
commit 76f3b97e56c69fc6ebce492a825befd311e57c4d
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60QFD

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76f3b97e56c69fc6ebce492a825befd311e57c4d



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

commit 45e1058b upstream.

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: 578b881b ("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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>