Re: [PATCH net-next v3 1/4] scm: add SO_PASSPIDFD and SCM_PIDFD

From: Aleksandr Mikhalitsyn
Date: Thu Apr 13 2023 - 09:42:45 EST

Fixed in -v4

https://lore.kernel.org/netdev/20230413133355.350571-2-aleksandr.mikhalitsyn@xxxxxxxxxxxxx/T/#u

Kind regards,
Alex


On Tue, Apr 11, 2023 at 5:37 PM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Tue, Apr 11, 2023 at 12:42:28PM +0200, Alexander Mikhalitsyn wrote:
> > Implement SCM_PIDFD, a new type of CMSG type analogical to SCM_CREDENTIALS,
> > but it contains pidfd instead of plain pid, which allows programmers not
> > to care about PID reuse problem.
> >
> > Idea comes from UAPI kernel group:
> > https://uapi-group.org/kernel-features/
> >
> > Big thanks to Christian Brauner and Lennart Poettering for productive
> > discussions about this.
> >
> > 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>
> > Cc: David Ahern <dsahern@xxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Christian Brauner <brauner@xxxxxxxxxx>
> > Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> > Cc: Lennart Poettering <mzxreary@xxxxxxxxxxx>
> > Cc: Luca Boccassi <bluca@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: netdev@xxxxxxxxxxxxxxx
> > Cc: linux-arch@xxxxxxxxxxxxxxx
> > Tested-by: Luca Boccassi <bluca@xxxxxxxxxx>
> > Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > ---
> > v2:
> > According to review comments from Kuniyuki Iwashima and Christian Brauner:
> > - use pidfd_create(..) retval as a result
> > - whitespace change
> > ---
> > arch/alpha/include/uapi/asm/socket.h | 2 ++
> > arch/mips/include/uapi/asm/socket.h | 2 ++
> > arch/parisc/include/uapi/asm/socket.h | 2 ++
> > arch/sparc/include/uapi/asm/socket.h | 2 ++
> > include/linux/net.h | 1 +
> > include/linux/socket.h | 1 +
> > include/net/scm.h | 14 ++++++++++++--
> > include/uapi/asm-generic/socket.h | 2 ++
> > net/core/sock.c | 11 +++++++++++
> > net/mptcp/sockopt.c | 1 +
> > net/unix/af_unix.c | 18 +++++++++++++-----
> > tools/include/uapi/asm-generic/socket.h | 2 ++
> > 12 files changed, 51 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
> > index 739891b94136..ff310613ae64 100644
> > --- a/arch/alpha/include/uapi/asm/socket.h
> > +++ b/arch/alpha/include/uapi/asm/socket.h
> > @@ -137,6 +137,8 @@
> >
> > #define SO_RCVMARK 75
> >
> > +#define SO_PASSPIDFD 76
> > +
> > #if !defined(__KERNEL__)
> >
> > #if __BITS_PER_LONG == 64
> > diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
> > index 18f3d95ecfec..762dcb80e4ec 100644
> > --- a/arch/mips/include/uapi/asm/socket.h
> > +++ b/arch/mips/include/uapi/asm/socket.h
> > @@ -148,6 +148,8 @@
> >
> > #define SO_RCVMARK 75
> >
> > +#define SO_PASSPIDFD 76
> > +
> > #if !defined(__KERNEL__)
> >
> > #if __BITS_PER_LONG == 64
> > diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
> > index f486d3dfb6bb..df16a3e16d64 100644
> > --- a/arch/parisc/include/uapi/asm/socket.h
> > +++ b/arch/parisc/include/uapi/asm/socket.h
> > @@ -129,6 +129,8 @@
> >
> > #define SO_RCVMARK 0x4049
> >
> > +#define SO_PASSPIDFD 0x404A
> > +
> > #if !defined(__KERNEL__)
> >
> > #if __BITS_PER_LONG == 64
> > diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
> > index 2fda57a3ea86..6e2847804fea 100644
> > --- a/arch/sparc/include/uapi/asm/socket.h
> > +++ b/arch/sparc/include/uapi/asm/socket.h
> > @@ -130,6 +130,8 @@
> >
> > #define SO_RCVMARK 0x0054
> >
> > +#define SO_PASSPIDFD 0x0055
> > +
> > #if !defined(__KERNEL__)
> >
> >
> > diff --git a/include/linux/net.h b/include/linux/net.h
> > index b73ad8e3c212..c234dfbe7a30 100644
> > --- a/include/linux/net.h
> > +++ b/include/linux/net.h
> > @@ -43,6 +43,7 @@ struct net;
> > #define SOCK_PASSSEC 4
> > #define SOCK_SUPPORT_ZC 5
> > #define SOCK_CUSTOM_SOCKOPT 6
> > +#define SOCK_PASSPIDFD 7
> >
> > #ifndef ARCH_HAS_SOCKET_TYPES
> > /**
> > diff --git a/include/linux/socket.h b/include/linux/socket.h
> > index 13c3a237b9c9..6bf90f251910 100644
> > --- a/include/linux/socket.h
> > +++ b/include/linux/socket.h
> > @@ -177,6 +177,7 @@ static inline size_t msg_data_left(struct msghdr *msg)
> > #define SCM_RIGHTS 0x01 /* rw: access rights (array of int) */
> > #define SCM_CREDENTIALS 0x02 /* rw: struct ucred */
> > #define SCM_SECURITY 0x03 /* rw: security label */
> > +#define SCM_PIDFD 0x04 /* ro: pidfd (int) */
> >
> > struct ucred {
> > __u32 pid;
> > diff --git a/include/net/scm.h b/include/net/scm.h
> > index 585adc1346bd..0c717ae9c8db 100644
> > --- a/include/net/scm.h
> > +++ b/include/net/scm.h
> > @@ -124,8 +124,9 @@ 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 ||
> > - scm_has_secdata(sock))
> > + if (test_bit(SOCK_PASSCRED, &sock->flags) ||
> > + test_bit(SOCK_PASSPIDFD, &sock->flags) ||
> > + scm->fp || scm_has_secdata(sock))
> > msg->msg_flags |= MSG_CTRUNC;
> > scm_destroy(scm);
> > return;
> > @@ -141,6 +142,15 @@ static __inline__ void scm_recv(struct socket *sock, struct msghdr *msg,
> > put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
> > }
> >
> > + if (test_bit(SOCK_PASSPIDFD, &sock->flags)) {
> > + int pidfd;
> > +
> > + WARN_ON_ONCE(!scm->pid);
> > + pidfd = pidfd_create(scm->pid, 0);
> > +
> > + put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd);
>
> I know you already mentioned that you accidently missed to change this
> to not leak an fd. But just so we keep track of it see the comment to v2
> https://lore.kernel.org/netdev/20230322154817.c6qasnixow452e6x@wittgenstein/#t