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[PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY

Matthieu Baerts (NGI0) posted 3 patches 3 weeks, 6 days ago
[PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY
Posted by Matthieu Baerts (NGI0) 3 weeks, 6 days ago 
When adding a socket option support in MPTCP, both the get and set parts
are supposed to be implemented.

IPV6_V6ONLY support for the setsockopt part has been added a while ago,
but it looks like the get part got forgotten. It should have been
present as a way to verify a setting has been set as expected, and not
to act differently from TCP or any other socket types.

Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
to check the default value, before doing extra actions. On Linux, the
default value is 0, but this can be changed with the net.ipv6.bindv6only
sysctl knob. On Windows, it is set to 1 by default. So supporting the
get part, like for all other socket options, is important.

Everything was in place to expose it, just the last step was missing.
Only new code is added to cover this specific getsockopt(), that seems
safe.

Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/sockopt.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 505445a9598fafa1cde6d8f4a1a8635c3e778051..4b99eb796855e4578d14df90f9d1cc3f1cd5b8c7 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1430,6 +1430,20 @@ static int mptcp_getsockopt_v4(struct mptcp_sock *msk, int optname,
 	return -EOPNOTSUPP;
 }
 
+static int mptcp_getsockopt_v6(struct mptcp_sock *msk, int optname,
+			       char __user *optval, int __user *optlen)
+{
+	struct sock *sk = (void *)msk;
+
+	switch (optname) {
+	case IPV6_V6ONLY:
+		return mptcp_put_int_option(msk, optval, optlen,
+					    sk->sk_ipv6only);
+	}
+
+	return -EOPNOTSUPP;
+}
+
 static int mptcp_getsockopt_sol_mptcp(struct mptcp_sock *msk, int optname,
 				      char __user *optval, int __user *optlen)
 {
@@ -1469,6 +1483,8 @@ int mptcp_getsockopt(struct sock *sk, int level, int optname,
 
 	if (level == SOL_IP)
 		return mptcp_getsockopt_v4(msk, optname, optval, option);
+	if (level == SOL_IPV6)
+		return mptcp_getsockopt_v6(msk, optname, optval, option);
 	if (level == SOL_TCP)
 		return mptcp_getsockopt_sol_tcp(msk, optname, optval, option);
 	if (level == SOL_MPTCP)

-- 
2.48.1
Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY
Posted by Simon Horman 3 weeks, 1 day ago 
On Fri, Mar 14, 2025 at 09:11:32PM +0100, Matthieu Baerts (NGI0) wrote:
> When adding a socket option support in MPTCP, both the get and set parts
> are supposed to be implemented.
> 
> IPV6_V6ONLY support for the setsockopt part has been added a while ago,
> but it looks like the get part got forgotten. It should have been
> present as a way to verify a setting has been set as expected, and not
> to act differently from TCP or any other socket types.
> 
> Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
> to check the default value, before doing extra actions. On Linux, the
> default value is 0, but this can be changed with the net.ipv6.bindv6only
> sysctl knob. On Windows, it is set to 1 by default. So supporting the
> get part, like for all other socket options, is important.
> 
> Everything was in place to expose it, just the last step was missing.
> Only new code is added to cover this specific getsockopt(), that seems
> safe.
> 
> Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
> Cc: stable@vger.kernel.org
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
> Reviewed-by: Mat Martineau <martineau@kernel.org>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Hi Matthieu, all,

TBH, I would lean towards this being net-next material rather than a fix
for net. But that notwithstanding this looks good to me.

Reviewed-by: Simon Horman <horms@kernel.org>
Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY
Posted by Matthieu Baerts 3 weeks, 1 day ago 
Hi Simon,

Thank you for your review!

On 19/03/2025 16:38, Simon Horman wrote:
> On Fri, Mar 14, 2025 at 09:11:32PM +0100, Matthieu Baerts (NGI0) wrote:
>> When adding a socket option support in MPTCP, both the get and set parts
>> are supposed to be implemented.
>>
>> IPV6_V6ONLY support for the setsockopt part has been added a while ago,
>> but it looks like the get part got forgotten. It should have been
>> present as a way to verify a setting has been set as expected, and not
>> to act differently from TCP or any other socket types.
>>
>> Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
>> to check the default value, before doing extra actions. On Linux, the
>> default value is 0, but this can be changed with the net.ipv6.bindv6only
>> sysctl knob. On Windows, it is set to 1 by default. So supporting the
>> get part, like for all other socket options, is important.
>>
>> Everything was in place to expose it, just the last step was missing.
>> Only new code is added to cover this specific getsockopt(), that seems
>> safe.
>>
>> Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
>> Cc: stable@vger.kernel.org
>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
>> Reviewed-by: Mat Martineau <martineau@kernel.org>
>> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> 
> Hi Matthieu, all,
> 
> TBH, I would lean towards this being net-next material rather than a fix
> for net. But that notwithstanding this looks good to me.
I understand. This patch and the next one target "net" because, with
MPTCP, we try to mimic TCP when interacting with the userspace.

Not supporting "getsockopt(IPV6_V6ONLY)" breaks some legacy apps forced
to use MPTCP instead of TCP. These apps apparently "strangely" check
this "getsockopt(IPV6_V6ONLY)" before changing the behaviour with
"setsockopt(IPV6_V6ONLY)" which is supported for a long time. The "get"
part should have been added from the beginning, and I don't see this
patch as a new feature. Because it simply sets an integer like most
other "get" options, it seems better to target net and fix these apps
ASAP rather than targeting net-next and delay this "safe" fix.

If that's OK, I would then prefer if these patches are applied in "net".
Or they can be applied in "net-next" if we can keep their "Cc: stable"
and "Fixes" tags, but that looks strange.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.
Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY
Posted by Simon Horman 3 weeks ago 
On Wed, Mar 19, 2025 at 05:26:35PM +0100, Matthieu Baerts wrote:
> Hi Simon,
> 
> Thank you for your review!
> 
> On 19/03/2025 16:38, Simon Horman wrote:
> > On Fri, Mar 14, 2025 at 09:11:32PM +0100, Matthieu Baerts (NGI0) wrote:
> >> When adding a socket option support in MPTCP, both the get and set parts
> >> are supposed to be implemented.
> >>
> >> IPV6_V6ONLY support for the setsockopt part has been added a while ago,
> >> but it looks like the get part got forgotten. It should have been
> >> present as a way to verify a setting has been set as expected, and not
> >> to act differently from TCP or any other socket types.
> >>
> >> Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
> >> to check the default value, before doing extra actions. On Linux, the
> >> default value is 0, but this can be changed with the net.ipv6.bindv6only
> >> sysctl knob. On Windows, it is set to 1 by default. So supporting the
> >> get part, like for all other socket options, is important.
> >>
> >> Everything was in place to expose it, just the last step was missing.
> >> Only new code is added to cover this specific getsockopt(), that seems
> >> safe.
> >>
> >> Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
> >> Cc: stable@vger.kernel.org
> >> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
> >> Reviewed-by: Mat Martineau <martineau@kernel.org>
> >> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> > 
> > Hi Matthieu, all,
> > 
> > TBH, I would lean towards this being net-next material rather than a fix
> > for net. But that notwithstanding this looks good to me.
> I understand. This patch and the next one target "net" because, with
> MPTCP, we try to mimic TCP when interacting with the userspace.
> 
> Not supporting "getsockopt(IPV6_V6ONLY)" breaks some legacy apps forced
> to use MPTCP instead of TCP. These apps apparently "strangely" check
> this "getsockopt(IPV6_V6ONLY)" before changing the behaviour with
> "setsockopt(IPV6_V6ONLY)" which is supported for a long time. The "get"
> part should have been added from the beginning, and I don't see this
> patch as a new feature. Because it simply sets an integer like most
> other "get" options, it seems better to target net and fix these apps
> ASAP rather than targeting net-next and delay this "safe" fix.
> 
> If that's OK, I would then prefer if these patches are applied in "net".
> Or they can be applied in "net-next" if we can keep their "Cc: stable"
> and "Fixes" tags, but that looks strange.

Hi Matthieu,

Thanks for your detailed explanation.
With that in mind I agree that these seem appropriate for net.
Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY
Posted by Paolo Abeni 3 weeks ago 
On 3/19/25 5:26 PM, Matthieu Baerts wrote:
> On 19/03/2025 16:38, Simon Horman wrote:
>> On Fri, Mar 14, 2025 at 09:11:32PM +0100, Matthieu Baerts (NGI0) wrote:
>>> When adding a socket option support in MPTCP, both the get and set parts
>>> are supposed to be implemented.
>>>
>>> IPV6_V6ONLY support for the setsockopt part has been added a while ago,
>>> but it looks like the get part got forgotten. It should have been
>>> present as a way to verify a setting has been set as expected, and not
>>> to act differently from TCP or any other socket types.
>>>
>>> Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
>>> to check the default value, before doing extra actions. On Linux, the
>>> default value is 0, but this can be changed with the net.ipv6.bindv6only
>>> sysctl knob. On Windows, it is set to 1 by default. So supporting the
>>> get part, like for all other socket options, is important.
>>>
>>> Everything was in place to expose it, just the last step was missing.
>>> Only new code is added to cover this specific getsockopt(), that seems
>>> safe.
>>>
>>> Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
>>> Cc: stable@vger.kernel.org
>>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
>>> Reviewed-by: Mat Martineau <martineau@kernel.org>
>>> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
>>
>> Hi Matthieu, all,
>>
>> TBH, I would lean towards this being net-next material rather than a fix
>> for net. But that notwithstanding this looks good to me.
> I understand. This patch and the next one target "net" because, with
> MPTCP, we try to mimic TCP when interacting with the userspace.
> 
> Not supporting "getsockopt(IPV6_V6ONLY)" breaks some legacy apps forced
> to use MPTCP instead of TCP. These apps apparently "strangely" check
> this "getsockopt(IPV6_V6ONLY)" before changing the behaviour with
> "setsockopt(IPV6_V6ONLY)" which is supported for a long time. The "get"
> part should have been added from the beginning, and I don't see this
> patch as a new feature. Because it simply sets an integer like most
> other "get" options, it seems better to target net and fix these apps
> ASAP rather than targeting net-next and delay this "safe" fix.
> 
> If that's OK, I would then prefer if these patches are applied in "net".
> Or they can be applied in "net-next" if we can keep their "Cc: stable"
> and "Fixes" tags, but that looks strange.

As per off-line discussion I'm going to apply only the first patch in
this series to net, and leave the other for net-next.

/P

Patchew 2.1-devel-b67e4c2

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