linux-kernel - hippi: incorrect address masking and compare operation

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Message-ID: <8931251f-b24a-5043-3bdd-f6ea810759f3@canonical.com>
Date:   Fri, 2 Jul 2021 11:42:17 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Jes Sorensen <jes@...ined-monkey.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "open list:HIPPI" <linux-hippi@...site.dk>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: hippi: incorrect address masking and compare operation

Hi,

Static analysis with Coverity has detected an issue in
drivers/net/hippi/rrunner.c where a masking operation and a comparison
is always false.

The analysis is as follows:

656                /*
657                 * Sanity test to see if we conflict with the DMA
658                 * limitations of the Roadrunner.
659                 */

Operands don't affect result (CONSTANT_EXPRESSION_RESULT)
dead_error_condition: The condition ((unsigned long)skb->data & 0xfffUL)
> 18446744073709486295UL cannot be true.

660                if ((((unsigned long)skb->data) & 0xfff) > ~65320)

Logically dead code (DEADCODE)dead_error_line: Execution cannot reach
this statement: printk("skb alloc error\n");.

661                        printk("skb alloc error\n");
662

I suspect the masking 0xfff is incorrect here, I think it be ~0xfff but
I'm not 100% sure.

Colin