Re: [PATCH 1/1] sctp: sysctl: referring the correct net namespace

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Thu, Nov 24, 2022 at 02:29:38PM +0800, Firo Yang wrote:
> The 11/23/2022 10:00, Marcelo Ricardo Leitner wrote:
> > On Wed, Nov 23, 2022 at 05:44:06PM +0800, Firo Yang wrote:
> > > Recently, a customer reported that from their container whose
> > > net namespace is different to the host's init_net, they can't set
> > > the container's net.sctp.rto_max to any value smaller than
> > > init_net.sctp.rto_min.
> > > 
> > > For instance,
> > > Host:
> > > sudo sysctl net.sctp.rto_min
> > > net.sctp.rto_min = 1000
> > > 
> > > Container:
> > > echo 100 > /mnt/proc-net/sctp/rto_min
> > > echo 400 > /mnt/proc-net/sctp/rto_max
> > > echo: write error: Invalid argument
> > > 
> > > This is caused by the check made from this'commit 4f3fdf3bc59c
> > > ("sctp: add check rto_min and rto_max in sysctl")'
> > > When validating the input value, it's always referring the boundary
> > > value set for the init_net namespace.
> > > 
> > > Having container's rto_max smaller than host's init_net.sctp.rto_min
> > > does make sense. Considering that the rto between two containers on the
> > > same host is very likely smaller than it for two hosts.
> > 
> > Makes sense. And also, here, it is not using the init_net as
> > boundaries for the values themselves. I mean, rto_min in init_net
> > won't be the minimum allowed for rto_min in other netns. Ditto for
> > rto_max.
> > 
> > More below.
> > 
> > > 
> > > So to fix this problem, just referring the boundary value from the net
> > > namespace where the new input value came from shold be enough.
> > > 
> > > Signed-off-by: Firo Yang <firo.yang@suse.com>
> > > ---
> > >  net/sctp/sysctl.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
> > > index b46a416787ec..e167df4dc60b 100644
> > > --- a/net/sctp/sysctl.c
> > > +++ b/net/sctp/sysctl.c
> > > @@ -429,6 +429,9 @@ static int proc_sctp_do_rto_min(struct ctl_table *ctl, int write,
> > >  	else
> > >  		tbl.data = &net->sctp.rto_min;
> > >  
> > > +	if (net != &init_net)
> > > +		max = net->sctp.rto_max;
> > 
> > This also affects other sysctls:
> > 
> > $ grep -e procname -e extra sysctl.c | grep -B1 extra.*init_net
> >                 .extra1         = SYSCTL_ONE,
> >                 .extra2         = &init_net.sctp.rto_max
> >                 .procname       = "rto_max",
> >                 .extra1         = &init_net.sctp.rto_min,
> > --
> >                 .extra1         = SYSCTL_ZERO,
> >                 .extra2         = &init_net.sctp.ps_retrans,
> >                 .procname       = "ps_retrans",
> >                 .extra1         = &init_net.sctp.pf_retrans,
> > 
> > And apparently, SCTP is the only one doing such dynamic limits. At
> > least in networking.
> > 
> > While the issue you reported is fixable this way, for ps/pf_retrans,
> > it is not, as it is using proc_dointvec_minmax() and it will simply
> > consume those values (with no netns translation).
> > 
> > So what about patching sctp_sysctl_net_register() instead, to update
> > these pointers during netns creation? Right after where it update the
> > 'data' one in there:
> > 
> >         for (i = 0; table[i].data; i++)
> >                 table[i].data += (char *)(&net->sctp) - (char *)&init_net.sctp;
> 
> Thanks Marcelo. It's better. So you mean something like the following?

Yes,

> 
> --- a/net/sctp/sysctl.c
> +++ b/net/sctp/sysctl.c
> @@ -586,6 +586,11 @@ int sctp_sysctl_net_register(struct net *net)
>         for (i = 0; table[i].data; i++)
>                 table[i].data += (char *)(&net->sctp) - (char *)&init_net.sctp;
>  
> +#define SCTP_RTO_MIN_IDX 1
> +#define SCTP_RTO_MAX_IDX 2

But these should be together with the sysctl table definition, so we
don't forget to update it later on if needed.

> +       table[SCTP_RTO_MIN_IDX].extra2 = &net->sctp.rto_max;
> +       table[SCTP_RTO_MAX_IDX].extra1 = &net->sctp.rto_min;

And also the ps/pf_retrans. :-)

> +
>         net->sctp.sysctl_header = register_net_sysctl(net, "net/sctp", table);
>         if (net->sctp.sysctl_header == NULL) {
>                 kfree(table);
> 
> 
> > 
> > Thanks,
> > Marcelo
> > 
> > > +
> > >  	ret = proc_dointvec(&tbl, write, buffer, lenp, ppos);
> > >  	if (write && ret == 0) {
> > >  		if (new_value > max || new_value < min)
> > > @@ -457,6 +460,9 @@ static int proc_sctp_do_rto_max(struct ctl_table *ctl, int write,
> > >  	else
> > >  		tbl.data = &net->sctp.rto_max;
> > >  
> > > +	if (net != &init_net)
> > > +		min = net->sctp.rto_min;
> > > +
> > >  	ret = proc_dointvec(&tbl, write, buffer, lenp, ppos);
> > >  	if (write && ret == 0) {
> > >  		if (new_value > max || new_value < min)
> > > -- 
> > > 2.26.2
> > >