netdev - Re: Unix domain socket missing error code

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Date:   Wed, 13 Nov 2019 14:00:48 +0100
From:   Adeel Sharif <madeel.sharif@...glemail.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Unix domain socket missing error code

Eventually Kernel OOM will start and kill the process:

[  581.134746] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1ubuntu1 04/01/2014
[  581.134816] Call Trace:
[  581.135550]  dump_stack+0x46/0x5b
[  581.135580]  dump_header.isra.35+0x5b/0x23c
[  581.135590]  oom_kill_process+0x20f/0x3d0
[  581.135603]  ? has_intersects_mems_allowed+0x6b/0x90
[  581.135623]  out_of_memory+0xe9/0x580
[  581.135630]  __alloc_pages_slowpath+0x9c9/0xd10
[  581.135640]  __alloc_pages_nodemask+0x237/0x260
[  581.135647]  filemap_fault+0x1eb/0x560
[  581.135656]  ? __switch_to_asm+0x40/0x70
[  581.135662]  ? __switch_to_asm+0x34/0x70
[  581.135667]  ? __switch_to_asm+0x40/0x70
[  581.135672]  ? alloc_set_pte+0x252/0x2f0
[  581.135680]  ext4_filemap_fault+0x27/0x36
[  581.135689]  __do_fault+0x2b/0x90
[  581.135694]  __handle_mm_fault+0x67e/0xae0
[  581.135704]  __do_page_fault+0x239/0x4b0
[  581.135713]  ? page_fault+0x8/0x30
[  581.135719]  page_fault+0x1e/0x30
[  581.135867] RIP: 0033:0x561979ac3050
[  581.136120] Code: Bad RIP value.
[  581.136140] RSP: 002b:00007ffe528f8668 EFLAGS: 00000246
[  581.136162] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00007fd49d85615d
[  581.136170] RDX: 000056197b832ac0 RSI: 000056197b832ae0 RDI: 000056197b82da30
[  581.136177] RBP: 000056197b82da30 R08: 00007ffe528f86e0 R09: 00007ffe5292d080
[  581.136184] R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000245
[  581.136191] R13: 0000561979b357e0 R14: 0000000000000003 R15: 00007ffe528f86e0

On Tue, Nov 12, 2019 at 9:56 AM Adeel Sharif
<madeel.sharif@...glemail.com> wrote:
>
> It should but it is not used when two different sockets are communicating.
> This is the third check in the if statement and it is never called
> because the first unlikely check was false:
>
> if (other != sk &&
>         unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
>
> Thanks.
>
> On Tue, Nov 12, 2019 at 1:12 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > 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.