On Mon, Mar 13, 2023 at 7:40 AM Aleksandr Mikhalitsyn
<aleksandr.mikhalitsyn@xxxxxxxxxxxxx> wrote:
>
> +CC security subsystem folks
>
> On Mon, Mar 13, 2023 at 12:32 PM Alexander Mikhalitsyn
> <aleksandr.mikhalitsyn@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> > Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> > Cc: Leon Romanovsky <leon@xxxxxxxxxx>
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> >
> > 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
