[PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[Alexander Mikhalitsyn]

Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.

For some reason we have no corresponding check for SO_PASSSEC.

In the recvmsg(2) doc we have:
       MSG_CTRUNC
              indicates that some control data was discarded due to lack
              of space in the buffer for ancillary data.

So, we need to set MSG_CTRUNC flag for all types of SCM.

This change can break applications those don't check MSG_CTRUNC flag.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Leon Romanovsky <leon@kernel.org>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>

v2:
- commit message was rewritten according to Eric's suggestion
---
 include/net/scm.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/net/scm.h b/include/net/scm.h
index 1ce365f4c256..585adc1346bd 100644
--- a/include/net/scm.h
+++ b/include/net/scm.h
@@ -105,16 +105,27 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
 		}
 	}
 }
+
+static inline bool scm_has_secdata(struct socket *sock)
+{
+	return test_bit(SOCK_PASSSEC, &sock->flags);
+}
 #else
 static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
 { }
+
+static inline bool scm_has_secdata(struct socket *sock)
+{
+	return false;
+}
 #endif /* CONFIG_SECURITY_NETWORK */
 
 static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
 				struct scm_cookie *scm, int flags)
 {
 	if (!msg->msg_control) {
-		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
+		if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
+		    scm_has_secdata(sock))
 			msg->msg_flags |= MSG_CTRUNC;
 		scm_destroy(scm);
 		return;
-- 
2.34.1

Re: [PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[Aleksandr Mikhalitsyn]

+CC security subsystem folks

On Mon, Mar 13, 2023 at 12:32 PM Alexander Mikhalitsyn
<aleksandr.mikhalitsyn@canonical.com> wrote:
>
> Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
> wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.
>
> For some reason we have no corresponding check for SO_PASSSEC.
>
> In the recvmsg(2) doc we have:
>        MSG_CTRUNC
>               indicates that some control data was discarded due to lack
>               of space in the buffer for ancillary data.
>
> So, we need to set MSG_CTRUNC flag for all types of SCM.
>
> This change can break applications those don't check MSG_CTRUNC flag.
>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Leon Romanovsky <leon@kernel.org>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
>
> v2:
> - commit message was rewritten according to Eric's suggestion
> ---
>  include/net/scm.h | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/scm.h b/include/net/scm.h
> index 1ce365f4c256..585adc1346bd 100644
> --- a/include/net/scm.h
> +++ b/include/net/scm.h
> @@ -105,16 +105,27 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
>                 }
>         }
>  }
> +
> +static inline bool scm_has_secdata(struct socket *sock)
> +{
> +       return test_bit(SOCK_PASSSEC, &sock->flags);
> +}
>  #else
>  static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
>  { }
> +
> +static inline bool scm_has_secdata(struct socket *sock)
> +{
> +       return false;
> +}
>  #endif /* CONFIG_SECURITY_NETWORK */
>
>  static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
>                                 struct scm_cookie *scm, int flags)
>  {
>         if (!msg->msg_control) {
> -               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
> +               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
> +                   scm_has_secdata(sock))
>                         msg->msg_flags |= MSG_CTRUNC;
>                 scm_destroy(scm);
>                 return;
> --
> 2.34.1
>

Re: [PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[Paul Moore]

On Mon, Mar 13, 2023 at 7:40 AM Aleksandr Mikhalitsyn
<aleksandr.mikhalitsyn@canonical.com> wrote:
>
> +CC security subsystem folks
>
> On Mon, Mar 13, 2023 at 12:32 PM Alexander Mikhalitsyn
> <aleksandr.mikhalitsyn@canonical.com> wrote:
> >
> > Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
> > wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.
> >
> > For some reason we have no corresponding check for SO_PASSSEC.
> >
> > In the recvmsg(2) doc we have:
> >        MSG_CTRUNC
> >               indicates that some control data was discarded due to lack
> >               of space in the buffer for ancillary data.
> >
> > So, we need to set MSG_CTRUNC flag for all types of SCM.
> >
> > This change can break applications those don't check MSG_CTRUNC flag.

Unless I'm missing something I don't think this will actually result
in a userspace visible change as put_cmsg() already has a number of
checks which set the MSG_CTRUNC flag if necessary (including if no
control buffer is passed, e.g. msg_control == NULL).

Regardless, it looks fine to me.

Acked-by: Paul Moore <paul@paul-moore.com>

> > Cc: "David S. Miller" <davem@davemloft.net>
> > Cc: Eric Dumazet <edumazet@google.com>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Paolo Abeni <pabeni@redhat.com>
> > Cc: Leon Romanovsky <leon@kernel.org>
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> >
> > v2:
> > - commit message was rewritten according to Eric's suggestion
> > ---
> >  include/net/scm.h | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/net/scm.h b/include/net/scm.h
> > index 1ce365f4c256..585adc1346bd 100644
> > --- a/include/net/scm.h
> > +++ b/include/net/scm.h
> > @@ -105,16 +105,27 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
> >                 }
> >         }
> >  }
> > +
> > +static inline bool scm_has_secdata(struct socket *sock)
> > +{
> > +       return test_bit(SOCK_PASSSEC, &sock->flags);
> > +}
> >  #else
> >  static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
> >  { }
> > +
> > +static inline bool scm_has_secdata(struct socket *sock)
> > +{
> > +       return false;
> > +}
> >  #endif /* CONFIG_SECURITY_NETWORK */
> >
> >  static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
> >                                 struct scm_cookie *scm, int flags)
> >  {
> >         if (!msg->msg_control) {
> > -               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
> > +               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
> > +                   scm_has_secdata(sock))
> >                         msg->msg_flags |= MSG_CTRUNC;
> >                 scm_destroy(scm);
> >                 return;
> > --
> > 2.34.1

-- 
paul-moore.com

Re: [PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[Aleksandr Mikhalitsyn]

On Mon, Mar 13, 2023 at 9:43 PM Paul Moore <paul@paul-moore.com> wrote:
>
> On Mon, Mar 13, 2023 at 7:40 AM Aleksandr Mikhalitsyn
> <aleksandr.mikhalitsyn@canonical.com> wrote:
> >
> > +CC security subsystem folks
> >
> > On Mon, Mar 13, 2023 at 12:32 PM Alexander Mikhalitsyn
> > <aleksandr.mikhalitsyn@canonical.com> wrote:
> > >
> > > Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
> > > wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.
> > >
> > > For some reason we have no corresponding check for SO_PASSSEC.
> > >
> > > In the recvmsg(2) doc we have:
> > >        MSG_CTRUNC
> > >               indicates that some control data was discarded due to lack
> > >               of space in the buffer for ancillary data.
> > >
> > > So, we need to set MSG_CTRUNC flag for all types of SCM.
> > >
> > > This change can break applications those don't check MSG_CTRUNC flag.
>
> Unless I'm missing something I don't think this will actually result
> in a userspace visible change as put_cmsg() already has a number of
> checks which set the MSG_CTRUNC flag if necessary (including if no
> control buffer is passed, e.g. msg_control == NULL).

Yes you are right. I found this check suspicious while working on
SCM_PIDFD (which is not yet submitted to LKML),
I think it is worth fixing that check anyway just for consistency reasons.

>
> Regardless, it looks fine to me.
>
> Acked-by: Paul Moore <paul@paul-moore.com>

Thanks, Paul!

Regards,
Alex

>
> > > Cc: "David S. Miller" <davem@davemloft.net>
> > > Cc: Eric Dumazet <edumazet@google.com>
> > > Cc: Jakub Kicinski <kuba@kernel.org>
> > > Cc: Paolo Abeni <pabeni@redhat.com>
> > > Cc: Leon Romanovsky <leon@kernel.org>
> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> > >
> > > v2:
> > > - commit message was rewritten according to Eric's suggestion
> > > ---
> > >  include/net/scm.h | 13 ++++++++++++-
> > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/net/scm.h b/include/net/scm.h
> > > index 1ce365f4c256..585adc1346bd 100644
> > > --- a/include/net/scm.h
> > > +++ b/include/net/scm.h
> > > @@ -105,16 +105,27 @@ static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct sc
> > >                 }
> > >         }
> > >  }
> > > +
> > > +static inline bool scm_has_secdata(struct socket *sock)
> > > +{
> > > +       return test_bit(SOCK_PASSSEC, &sock->flags);
> > > +}
> > >  #else
> > >  static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
> > >  { }
> > > +
> > > +static inline bool scm_has_secdata(struct socket *sock)
> > > +{
> > > +       return false;
> > > +}
> > >  #endif /* CONFIG_SECURITY_NETWORK */
> > >
> > >  static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
> > >                                 struct scm_cookie *scm, int flags)
> > >  {
> > >         if (!msg->msg_control) {
> > > -               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp)
> > > +               if (test_bit(SOCK_PASSCRED, &sock->flags) || scm->fp ||
> > > +                   scm_has_secdata(sock))
> > >                         msg->msg_flags |= MSG_CTRUNC;
> > >                 scm_destroy(scm);
> > >                 return;
> > > --
> > > 2.34.1
>
> --
> paul-moore.com

Re: [PATCH net-next v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by David S. Miller <davem@davemloft.net>:

On Mon, 13 Mar 2023 12:32:11 +0100 you wrote:
> Currently, kernel would set MSG_CTRUNC flag if msg_control buffer
> wasn't provided and SO_PASSCRED was set or if there was pending SCM_RIGHTS.
> 
> For some reason we have no corresponding check for SO_PASSSEC.
> 
> In the recvmsg(2) doc we have:
>        MSG_CTRUNC
>               indicates that some control data was discarded due to lack
>               of space in the buffer for ancillary data.
> 
> [...]

Here is the summary with links:
  - [net-next,v2] scm: fix MSG_CTRUNC setting condition for SO_PASSSEC
    https://git.kernel.org/netdev/net-next/c/a02d83f9947d

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html