netdev - re: mlxsw: spectrum: Adjust headroom buffers for 8x ports

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Date:   Wed, 17 Jun 2020 18:15:35 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Ido Schimmel <idosch@...lanox.com>
Cc:     Jiri Pirko <jiri@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Petr Machata <petrm@...lanox.com>, netdev@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: re: mlxsw: spectrum: Adjust headroom buffers for 8x ports

Hi

Static analysis with Coverity has detected an issue that relies on the
machine endianness to work. The commit in question is:

commit 60833d54d56c21e7538296eb2e00e104768fd047
Author: Ido Schimmel <idosch@...lanox.com>
Date:   Tue Jun 16 10:14:58 2020 +0300

    mlxsw: spectrum: Adjust headroom buffers for 8x ports

in line:
    mlxsw_sp_port_headroom_8x_adjust(mlxsw_sp_port, (u16 *) &buffsize);

The cast of the u32 buffsize to (u16 *) to scale buffsize in the call to
to mlxsw_sp_port_headroom_8x_adjust() will behave differently on big
endian architectures to that of little endian architectures.  I'm not
sure if this is intentional or not.

One solution is to either make buffsize a u16, but I am concerned this
may be incorrect as the buffsize is assigned from the call
mlxsw_sp_span_buffsize_get() and this returns a u32 so we may have
overflow issues. Probably better to make
mlxsw_sp_port_headroom_8x_adjust handle u32 integers and to return the
adjusted value rather than modifying it by pass-by-reference.

Colin