linux-kernel - Re: [PATCH v4 RESEND net-next] net: socket: use BIT() for MSG

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Date:   Wed, 17 Mar 2021 09:39:26 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     menglong8.dong@...il.com
Cc:     linux@...ck-us.net, andy.shevchenko@...il.com, kuba@...nel.org,
        axboe@...nel.dk, viro@...iv.linux.org.uk,
        herbert@...dor.apana.org.au, dong.menglong@....com.cn,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v4 RESEND net-next] net: socket: use BIT() for MSG_*

From: Menglong Dong <menglong8.dong@...il.com>
Date: Wed, 17 Mar 2021 16:21:14 +0800

> Hello,
> 
> On Wed, Mar 17, 2021 at 9:38 AM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On Wed, Mar 17, 2021 at 01:02:51AM +0200, Andy Shevchenko wrote:
>> > On Wednesday, March 17, 2021, Guenter Roeck <linux@...ck-us.net> wrote:
>> >
> ...
>>
>> The problem is in net/packet/af_packet.c:packet_recvmsg(). This function,
>> as well as all other rcvmsg functions, is declared as
>>
>> static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>>                           int flags)
>>
>> MSG_CMSG_COMPAT (0x80000000) is set in flags, meaning its value is negative.
>> This is then evaluated in
>>
>>        if (flags & ~(MSG_PEEK|MSG_DONTWAIT|MSG_TRUNC|MSG_CMSG_COMPAT|MSG_ERRQUEUE))
>>                 goto out;
> So what should I do? Revert this patch? Or fix the usages of 'flags'?

I already reverted this patch from net-next to fix the regression.