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

[Firo Yang]

The 11/24/2022 14:57, Marcelo Ricardo Leitner wrote:
> 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@xxxxxxxx>
> > > > ---
> > > >  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. :-)

Sure. I will send an V2.

Thanks,
// Firo

> 
> > +
> >         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
> > > >