[PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[Zheng Li]

From: Zheng Li <James.Z.Li@Dell.com>

Inter-process communication on localhost should be established successfully even the ARP table is full,
many processes on server machine use the localhost to communicate such as command-line interface (CLI),
servers hope all CLI commands can be executed successfully even the arp table is full.
Right now CLI commands got timeout when the arp table is full.
Set the parameter of exempt_from_gc to be true for LOOPBACK net device to
keep localhost neigh in arp table, not removed by gc.

the steps of reproduced:
server with "gc_thresh3 = 1024" setting, ping server from more than 1024 IPv4 addresses,
run "ssh localhost" on console interface, then the command will get timeout.

Signed-off-by: Zheng Li <James.Z.Li@Dell.com>
---
 net/core/neighbour.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 552719c3bbc3..d96dee3d4af6 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -734,7 +734,10 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 struct neighbour *__neigh_create(struct neigh_table *tbl, const void *pkey,
 				 struct net_device *dev, bool want_ref)
 {
-	return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
+	if (dev->flags & IFF_LOOPBACK)
+		return ___neigh_create(tbl, pkey, dev, 0, true, want_ref);
+	else
+		return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
 }
 EXPORT_SYMBOL(__neigh_create);
 
-- 
2.17.1

Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[Ratheesh Kannoth]

On 2024-03-11 at 17:54:01, Zheng Li (lizheng043@gmail.com) wrote:
>
> Inter-process communication on localhost should be established successfully even the ARP table is full,
> many processes on server machine use the localhost to communicate such as command-line interface (CLI),
> servers hope all CLI commands can be executed successfully even the arp table is full.
> Right now CLI commands got timeout when the arp table is full.
> Set the parameter of exempt_from_gc to be true for LOOPBACK net device to
> keep localhost neigh in arp table, not removed by gc.
>
> the steps of reproduced:
> server with "gc_thresh3 = 1024" setting, ping server from more than 1024 IPv4 addresses,
> run "ssh localhost" on console interface, then the command will get timeout.
it does not look correct to me. why gc has to behave differently for loopback devices.
why can't a higher gc_thresh3 value (fine tuned to your use case) wont solve the issue ?
can't you add localhost arp entry statically and get rid of gc issue ?

>
> Signed-off-by: Zheng Li <James.Z.Li@Dell.com>
> ---
>  net/core/neighbour.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 552719c3bbc3..d96dee3d4af6 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -734,7 +734,10 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
>  struct neighbour *__neigh_create(struct neigh_table *tbl, const void *pkey,
>  				 struct net_device *dev, bool want_ref)
>  {
> -	return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
> +	if (dev->flags & IFF_LOOPBACK)
> +		return ___neigh_create(tbl, pkey, dev, 0, true, want_ref);
> +	else
> +		return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
>  }
>  EXPORT_SYMBOL(__neigh_create);
>
> --
> 2.17.1
>

Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[James Lee]

loopback neigh is a special device in the neighbour system which is
used by all local communications and state is NUD_NOARP.
Any setting value of gc_thresh3 might encounter arp table be full,
manually increasing gc_thresh3 can resolve this issue for every time,
but we hope this issue automatically be resolved in Linux kernel for
all local communications whenever ARP table is full, rather than
manually operation as a workaround.


Ratheesh Kannoth <rkannoth@marvell.com> 于2024年3月11日周一 21:51写道：
>
> On 2024-03-11 at 17:54:01, Zheng Li (lizheng043@gmail.com) wrote:
> >
> > Inter-process communication on localhost should be established successfully even the ARP table is full,
> > many processes on server machine use the localhost to communicate such as command-line interface (CLI),
> > servers hope all CLI commands can be executed successfully even the arp table is full.
> > Right now CLI commands got timeout when the arp table is full.
> > Set the parameter of exempt_from_gc to be true for LOOPBACK net device to
> > keep localhost neigh in arp table, not removed by gc.
> >
> > the steps of reproduced:
> > server with "gc_thresh3 = 1024" setting, ping server from more than 1024 IPv4 addresses,
> > run "ssh localhost" on console interface, then the command will get timeout.
> it does not look correct to me. why gc has to behave differently for loopback devices.
> why can't a higher gc_thresh3 value (fine tuned to your use case) wont solve the issue ?
> can't you add localhost arp entry statically and get rid of gc issue ?
>
> >
> > Signed-off-by: Zheng Li <James.Z.Li@Dell.com>
> > ---
> >  net/core/neighbour.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> > index 552719c3bbc3..d96dee3d4af6 100644
> > --- a/net/core/neighbour.c
> > +++ b/net/core/neighbour.c
> > @@ -734,7 +734,10 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
> >  struct neighbour *__neigh_create(struct neigh_table *tbl, const void *pkey,
> >                                struct net_device *dev, bool want_ref)
> >  {
> > -     return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
> > +     if (dev->flags & IFF_LOOPBACK)
> > +             return ___neigh_create(tbl, pkey, dev, 0, true, want_ref);
> > +     else
> > +             return ___neigh_create(tbl, pkey, dev, 0, false, want_ref);
> >  }
> >  EXPORT_SYMBOL(__neigh_create);
> >
> > --
> > 2.17.1
> >

RE: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[Ratheesh Kannoth]

> From: James Lee <lizheng043@gmail.com>
> Sent: Monday, March 18, 2024 2:09 PM
> To: Ratheesh Kannoth <rkannoth@marvell.com>
> Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> James.Z.Li@dell.com
> Subject: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost
> connections be established successfully even the ARP table is full
> 
> Prioritize security for external emails: Confirm sender and content safety
> before clicking links or opening attachments
> 
> ----------------------------------------------------------------------
> loopback neigh is a special device in the neighbour system which is used by all
> local communications and state is NUD_NOARP.
> Any setting value of gc_thresh3 might encounter arp table be full, manually
> increasing gc_thresh3 can resolve this issue for every time, but we hope this
> issue automatically be resolved in Linux kernel for all local communications
> whenever ARP table is full, rather than manually operation as a workaround.

Issue is , these are dynamic entries which cannot be removed by gc.  And there is no
Threshold applicable on it.  I feel like, this may be exploited. 

Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[James Lee]

It's not an issue, the loopback device can only be created by kernel
itself, loopback neigh entry also can only be created by kernel, one
loopback neigh for ipv4 ,one for ipv6, impossible that the num of
loopback neigh entries exceeds 2.

Ratheesh Kannoth <rkannoth@marvell.com> 于2024年3月18日周一 23:36写道：
>
> > From: James Lee <lizheng043@gmail.com>
> > Sent: Monday, March 18, 2024 2:09 PM
> > To: Ratheesh Kannoth <rkannoth@marvell.com>
> > Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> > nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> > James.Z.Li@dell.com
> > Subject: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost
> > connections be established successfully even the ARP table is full
> >
> > Prioritize security for external emails: Confirm sender and content safety
> > before clicking links or opening attachments
> >
> > ----------------------------------------------------------------------
> > loopback neigh is a special device in the neighbour system which is used by all
> > local communications and state is NUD_NOARP.
> > Any setting value of gc_thresh3 might encounter arp table be full, manually
> > increasing gc_thresh3 can resolve this issue for every time, but we hope this
> > issue automatically be resolved in Linux kernel for all local communications
> > whenever ARP table is full, rather than manually operation as a workaround.
>
> Issue is , these are dynamic entries which cannot be removed by gc.  And there is no
> Threshold applicable on it.  I feel like, this may be exploited.
>

RE: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[Ratheesh Kannoth]

> From: James Lee <lizheng043@gmail.com>
> Sent: Tuesday, March 19, 2024 3:13 PM
> To: Ratheesh Kannoth <rkannoth@marvell.com>
> Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> James.Z.Li@dell.com
> Subject: Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost
> connections be established successfully even the ARP table is full
> 
> It's not an issue, the loopback device can only be created by kernel itself,
> loopback neigh entry also can only be created by kernel, one loopback neigh
> for ipv4 ,one for ipv6, impossible that the num of loopback neigh entries
> exceeds 2.
ACK. I still feel like a hack. Please post a new patch version. Let maintainers take a call. 

Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[James Lee]

It's not an issue, why need "post a new patch version"?

Ratheesh Kannoth <rkannoth@marvell.com> 于2024年3月22日周五 11:37写道：
>
> > From: James Lee <lizheng043@gmail.com>
> > Sent: Tuesday, March 19, 2024 3:13 PM
> > To: Ratheesh Kannoth <rkannoth@marvell.com>
> > Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> > nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> > James.Z.Li@dell.com
> > Subject: Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost
> > connections be established successfully even the ARP table is full
> >
> > It's not an issue, the loopback device can only be created by kernel itself,
> > loopback neigh entry also can only be created by kernel, one loopback neigh
> > for ipv4 ,one for ipv6, impossible that the num of loopback neigh entries
> > exceeds 2.
> ACK. I still feel like a hack. Please post a new patch version. Let maintainers take a call.

RE: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost connections be established successfully even the ARP table is full

[Ratheesh Kannoth]

> From: James Lee <lizheng043@gmail.com>
> Sent: Thursday, March 28, 2024 2:11 PM
> To: Ratheesh Kannoth <rkannoth@marvell.com>
> Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> James.Z.Li@dell.com; Simon Horman <horms@kernel.org>
> Subject: Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the localhost
> connections be established successfully even the ARP table is full
> 

> It's not an issue, 
Please don’t top post

 >why need "post a new patch version"?
ASFAIK, only https://patchwork.kernel.org/project/netdevbpf/list/ will be actively looked up to merge patches.
I could be wrong. 

> 
> Ratheesh Kannoth <rkannoth@marvell.com> 于2024年3月22日周五
> 11:37写道：
> >
> > > From: James Lee <lizheng043@gmail.com>
> > > Sent: Tuesday, March 19, 2024 3:13 PM
> > > To: Ratheesh Kannoth <rkannoth@marvell.com>
> > > Cc: linux-kernel@vger.kernel.org; netdev@vger.kernel.org;
> > > nhorman@tuxdriver.com; davem@davemloft.net; jmorris@namei.org;
> > > James.Z.Li@dell.com
> > > Subject: Re: [EXTERNAL] Re: [PATCH] neighbour: guarantee the
> > > localhost connections be established successfully even the ARP table
> > > is full
> > >
> > > It's not an issue, the loopback device can only be created by kernel
> > > itself, loopback neigh entry also can only be created by kernel, one
> > > loopback neigh for ipv4 ,one for ipv6, impossible that the num of
> > > loopback neigh entries exceeds 2.
> > ACK. I still feel like a hack. Please post a new patch version. Let maintainers
> take a call.