netdev - Re: Unix domain socket missing error code

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Date:   Mon, 11 Nov 2019 16:12:13 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Adeel Sharif <madeel.sharif@...glemail.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Unix domain socket missing error code

On Mon, Nov 11, 2019 at 5:41 AM Adeel Sharif
<madeel.sharif@...glemail.com> wrote:
>
> Hello,
>
> We are a group of people working on making Linux safe for everyone. In
> hope of doing that I started testing the System Calls. The one I am
> currently working on is send/write.
>
> If send() is used to send datagrams on unix socket and the receiver
> has stopped receiving, but still connected, there is a high
> possibility that Linux kernel could eat up the whole system memory.
> Although there is a system wide limit on write memory from wmem_max
> parameter but this is sometimes also increased to system momory size
> in order to avoid packet drops.
>
> After having a look in the kernel implementation of
> unix_dgram_sendmsg() it is obvious that user buffers are copied into
> kernel socket buffers and they are queued to a linked list. This list
> is growing without any limits. Although there is a qlen parameter but
> it is never used to impose a limit on it. Could we perhaps impose a
> limit on it and return an error with errcode Queue_Full or something
> instead?

Isn't unix_recvq_full() supposed to do what you said? It is called inside
unix_dgram_sendmsg() to determine whether to wake up the dst socket.

Thanks.