On Thu, Mar 16, 2023 at 10:53:20PM -0700, Kuniyuki Iwashima wrote:
> From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> Date: Thu, 16 Mar 2023 14:15:24 +0100
> > 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.
> >
> > 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: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: netdev@xxxxxxxxxxxxxxx
> > Cc: linux-arch@xxxxxxxxxxxxxxx
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> > ---
> > 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 | 16 +++++++++++++++-
> > 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, 54 insertions(+), 6 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..4617fbc65294 100644
> > --- a/include/net/scm.h
> > +++ b/include/net/scm.h
> > @@ -124,7 +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 ||
> > + if (test_bit(SOCK_PASSCRED, &sock->flags) ||
> > + test_bit(SOCK_PASSPIDFD, &sock->flags) ||
> > + scm->fp ||
>
> nit: I'd remove newline here.
>
>
> > scm_has_secdata(sock))
> > msg->msg_flags |= MSG_CTRUNC;
> > scm_destroy(scm);
> > @@ -141,6 +143,18 @@ 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;
> > +
> > + if (WARN_ON_ONCE(!scm->pid) ||
> > + !pid_has_task(scm->pid, PIDTYPE_TGID))
>
> Can we change pidfd_create() to return -ESRCH as it has the same test ?
I don't think we can do this. pidfd_create() can't distinguish between
"this task has been reaped" and "this is a non-thread group leader". So
EINVAL is a better hint especially since pidfd_open() is preceeded by a
check that would return -ESRCH.
It would also be a uapi change for the pidfd_open() syscall to change
pidfd_create() like that and for fanotify as well. Now they get EINVAL
for a non-thread group leader pid they pass into the system call.
Afterwards they'd get ESRCH which is at least misleading if not wrong.
