Coverity complains of a possible NULL dereference in
mptcp_getsockopt_subflow_addrs():

861        } else if (sk->sk_family == AF_INET6) {
    	3. returned_null: inet6_sk returns NULL. [show details]
    	4. var_assigned: Assigning: np = NULL return value from inet6_sk.
 862                const struct ipv6_pinfo *np = inet6_sk(sk);

Fix this by checking for NULL.

Cc: Mat Martineau <mathew.j.martineau@linux.intel.com>
Cc: Matthieu Baerts <matthieu.baerts@tessares.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Cc: mptcp@lists.linux.dev
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

[ I'm not at all sure this is the right thing to do since the final result is to
return garbage to user space in mptcp_getsockopt_subflow_addrs(). Is this one
of those cases where inet6_sk() can't fail ?]
---
 net/mptcp/sockopt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 8137cc3a4296..c89f2bedce79 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -861,6 +861,9 @@ static void mptcp_get_sub_addrs(const struct sock *sk, struct mptcp_subflow_addr
 	} else if (sk->sk_family == AF_INET6) {
 		const struct ipv6_pinfo *np = inet6_sk(sk);
 
+		if (!np)
+			return;
+
 		a->sin6_local.sin6_family = AF_INET6;
 		a->sin6_local.sin6_port = inet->inet_sport;
 
-- 
2.33.0

On Mon, 20 Sep 2021, Tim Gardner wrote:

> Coverity complains of a possible NULL dereference in
> mptcp_getsockopt_subflow_addrs():
>
> 861        } else if (sk->sk_family == AF_INET6) {
>    	3. returned_null: inet6_sk returns NULL. [show details]
>    	4. var_assigned: Assigning: np = NULL return value from inet6_sk.
> 862                const struct ipv6_pinfo *np = inet6_sk(sk);
>
> Fix this by checking for NULL.
>
> Cc: Mat Martineau <mathew.j.martineau@linux.intel.com>
> Cc: Matthieu Baerts <matthieu.baerts@tessares.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: netdev@vger.kernel.org
> Cc: mptcp@lists.linux.dev
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
>
> [ I'm not at all sure this is the right thing to do since the final result is to
> return garbage to user space in mptcp_getsockopt_subflow_addrs(). Is this one
> of those cases where inet6_sk() can't fail ?]

Hi Tim -

Thanks for noticing this and proposing a fix.

As you commented, this isn't the right change to merge since 
mptcp_getsockopt_subflow_addrs() would copy garbage.

This block of code already checks that CONFIG_IPV6 is enabled, so the 
question is whether sk_fullsock() would return false because the subflow 
is in TCP_TIME_WAIT or TCP_NEW_SYN_RECV. The caller is iterating over 
sockets in the MPTCP socket's conn_list, which does not contain 
request_socks (so there are no sockets in the TCP_NEW_SYN_RECV state).

TCP subflow sockets are normally removed from the conn_list before they 
are closed by their parent MPTCP socket, but I need to double-check for 
corner cases. I created a github issue to track this: 
https://github.com/multipath-tcp/mptcp_net-next/issues/231


Thanks,

Mat


> ---
> net/mptcp/sockopt.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
> index 8137cc3a4296..c89f2bedce79 100644
> --- a/net/mptcp/sockopt.c
> +++ b/net/mptcp/sockopt.c
> @@ -861,6 +861,9 @@ static void mptcp_get_sub_addrs(const struct sock *sk, struct mptcp_subflow_addr
> 	} else if (sk->sk_family == AF_INET6) {
> 		const struct ipv6_pinfo *np = inet6_sk(sk);
>
> +		if (!np)
> +			return;
> +
> 		a->sin6_local.sin6_family = AF_INET6;
> 		a->sin6_local.sin6_port = inet->inet_sport;
>
> -- 
> 2.33.0
>
>

--
Mat Martineau
Intel

On Mon, 20 Sep 2021, Mat Martineau wrote:

> On Mon, 20 Sep 2021, Tim Gardner wrote:
>
>> Coverity complains of a possible NULL dereference in
>> mptcp_getsockopt_subflow_addrs():
>> 
>> 861        } else if (sk->sk_family == AF_INET6) {
>>    	3. returned_null: inet6_sk returns NULL. [show details]
>>    	4. var_assigned: Assigning: np = NULL return value from inet6_sk.
>> 862                const struct ipv6_pinfo *np = inet6_sk(sk);
>> 
>> Fix this by checking for NULL.
>> 
>> Cc: Mat Martineau <mathew.j.martineau@linux.intel.com>
>> Cc: Matthieu Baerts <matthieu.baerts@tessares.net>
>> Cc: "David S. Miller" <davem@davemloft.net>
>> Cc: Jakub Kicinski <kuba@kernel.org>
>> Cc: netdev@vger.kernel.org
>> Cc: mptcp@lists.linux.dev
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
>> 
>> [ I'm not at all sure this is the right thing to do since the final result is to
>> return garbage to user space in mptcp_getsockopt_subflow_addrs(). Is this one
>> of those cases where inet6_sk() can't fail ?]
>
> Hi Tim -
>
> Thanks for noticing this and proposing a fix.
>
> As you commented, this isn't the right change to merge since 
> mptcp_getsockopt_subflow_addrs() would copy garbage.
>
> This block of code already checks that CONFIG_IPV6 is enabled, so the 
> question is whether sk_fullsock() would return false because the subflow is 
> in TCP_TIME_WAIT or TCP_NEW_SYN_RECV. The caller is iterating over sockets in 
> the MPTCP socket's conn_list, which does not contain request_socks (so there 
> are no sockets in the TCP_NEW_SYN_RECV state).
>
> TCP subflow sockets are normally removed from the conn_list before they are 
> closed by their parent MPTCP socket, but I need to double-check for corner 
> cases. I created a github issue to track this: 
> https://github.com/multipath-tcp/mptcp_net-next/issues/231
>

Tim,

Could you submit a v2 of this patch? Paolo took a look and the condition 
should not happen, but adding the NULL check would be a good idea and 
returning early as your patch does is ok. The data copied after the early 
return will be zeroed and look like the address family is AF_UNSPEC.

Could you add a

Fixes: https://github.com/multipath-tcp/mptcp_net-next/issues/231

tag and make the one change below?

>
>> ---
>> net/mptcp/sockopt.c | 3 +++
>> 1 file changed, 3 insertions(+)
>> 
>> diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
>> index 8137cc3a4296..c89f2bedce79 100644
>> --- a/net/mptcp/sockopt.c
>> +++ b/net/mptcp/sockopt.c
>> @@ -861,6 +861,9 @@ static void mptcp_get_sub_addrs(const struct sock *sk, 
>> struct mptcp_subflow_addr
>> 	} else if (sk->sk_family == AF_INET6) {
>> 		const struct ipv6_pinfo *np = inet6_sk(sk);
>> 
>> +		if (!np)

This could be

if (WARN_ON_ONCE(!np))

(as suggested by Paolo) to make it clear the condition is unexpected.

>> +			return;
>> +
>> 		a->sin6_local.sin6_family = AF_INET6;
>> 		a->sin6_local.sin6_port = inet->inet_sport;
>> 
>> -- 
>> 2.33.0

Thanks,

--
Mat Martineau
Intel