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scm: add SO_PASSPIDFD and SCM_PIDFD
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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@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>
Cc: David Ahern <dsahern@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: Lennart Poettering <mzxreary@0pointer.de>
Cc: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
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@mihalicyn @intel-lab-lkp
mihalicyn authored and intel-lab-lkp committed Mar 21, 2023
1 parent c8384d4 commit 491b690
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Showing 12 changed files with 51 additions and 7 deletions.
2 changes: 2 additions & 0 deletions arch/alpha/include/uapi/asm/socket.h
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Expand Up @@ -137,6 +137,8 @@

#define SO_RCVMARK 75

#define SO_PASSPIDFD 76

#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
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2 changes: 2 additions & 0 deletions arch/mips/include/uapi/asm/socket.h
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Expand Up @@ -148,6 +148,8 @@

#define SO_RCVMARK 75

#define SO_PASSPIDFD 76

#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
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2 changes: 2 additions & 0 deletions arch/parisc/include/uapi/asm/socket.h
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Expand Up @@ -129,6 +129,8 @@

#define SO_RCVMARK 0x4049

#define SO_PASSPIDFD 0x404A

#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64
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2 changes: 2 additions & 0 deletions arch/sparc/include/uapi/asm/socket.h
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Expand Up @@ -130,6 +130,8 @@

#define SO_RCVMARK 0x0054

#define SO_PASSPIDFD 0x0055

#if !defined(__KERNEL__)


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1 change: 1 addition & 0 deletions include/linux/net.h
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Expand Up @@ -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
/**
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1 change: 1 addition & 0 deletions include/linux/socket.h
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Expand Up @@ -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;
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14 changes: 12 additions & 2 deletions include/net/scm.h
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Expand Up @@ -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;
Expand All @@ -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);
}

scm_destroy_cred(scm);

scm_passec(sock, msg, scm);
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2 changes: 2 additions & 0 deletions include/uapi/asm-generic/socket.h
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Expand Up @@ -132,6 +132,8 @@

#define SO_RCVMARK 75

#define SO_PASSPIDFD 76

#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
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11 changes: 11 additions & 0 deletions net/core/sock.c
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Expand Up @@ -1246,6 +1246,13 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
clear_bit(SOCK_PASSCRED, &sock->flags);
break;

case SO_PASSPIDFD:
if (valbool)
set_bit(SOCK_PASSPIDFD, &sock->flags);
else
clear_bit(SOCK_PASSPIDFD, &sock->flags);
break;

case SO_TIMESTAMP_OLD:
case SO_TIMESTAMP_NEW:
case SO_TIMESTAMPNS_OLD:
Expand Down Expand Up @@ -1737,6 +1744,10 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
v.val = !!test_bit(SOCK_PASSCRED, &sock->flags);
break;

case SO_PASSPIDFD:
v.val = !!test_bit(SOCK_PASSPIDFD, &sock->flags);
break;

case SO_PEERCRED:
{
struct ucred peercred;
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1 change: 1 addition & 0 deletions net/mptcp/sockopt.c
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Expand Up @@ -355,6 +355,7 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
case SO_BROADCAST:
case SO_BSDCOMPAT:
case SO_PASSCRED:
case SO_PASSPIDFD:
case SO_PASSSEC:
case SO_RXQ_OVFL:
case SO_WIFI_STATUS:
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18 changes: 13 additions & 5 deletions net/unix/af_unix.c
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Expand Up @@ -1361,7 +1361,8 @@ static int unix_dgram_connect(struct socket *sock, struct sockaddr *addr,
if (err)
goto out;

if (test_bit(SOCK_PASSCRED, &sock->flags) &&
if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
test_bit(SOCK_PASSPIDFD, &sock->flags)) &&
!unix_sk(sk)->addr) {
err = unix_autobind(sk);
if (err)
Expand Down Expand Up @@ -1469,7 +1470,8 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
if (err)
goto out;

if (test_bit(SOCK_PASSCRED, &sock->flags) && !u->addr) {
if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
test_bit(SOCK_PASSPIDFD, &sock->flags)) && !u->addr) {
err = unix_autobind(sk);
if (err)
goto out;
Expand Down Expand Up @@ -1670,6 +1672,8 @@ static void unix_sock_inherit_flags(const struct socket *old,
{
if (test_bit(SOCK_PASSCRED, &old->flags))
set_bit(SOCK_PASSCRED, &new->flags);
if (test_bit(SOCK_PASSPIDFD, &old->flags))
set_bit(SOCK_PASSPIDFD, &new->flags);
if (test_bit(SOCK_PASSSEC, &old->flags))
set_bit(SOCK_PASSSEC, &new->flags);
}
Expand Down Expand Up @@ -1819,8 +1823,10 @@ static bool unix_passcred_enabled(const struct socket *sock,
const struct sock *other)
{
return test_bit(SOCK_PASSCRED, &sock->flags) ||
test_bit(SOCK_PASSPIDFD, &sock->flags) ||
!other->sk_socket ||
test_bit(SOCK_PASSCRED, &other->sk_socket->flags);
test_bit(SOCK_PASSCRED, &other->sk_socket->flags) ||
test_bit(SOCK_PASSPIDFD, &other->sk_socket->flags);
}

/*
Expand Down Expand Up @@ -1922,7 +1928,8 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
goto out;
}

if (test_bit(SOCK_PASSCRED, &sock->flags) && !u->addr) {
if ((test_bit(SOCK_PASSCRED, &sock->flags) ||
test_bit(SOCK_PASSPIDFD, &sock->flags)) && !u->addr) {
err = unix_autobind(sk);
if (err)
goto out;
Expand Down Expand Up @@ -2824,7 +2831,8 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
/* Never glue messages from different writers */
if (!unix_skb_scm_eq(skb, &scm))
break;
} else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
} else if (test_bit(SOCK_PASSCRED, &sock->flags) ||
test_bit(SOCK_PASSPIDFD, &sock->flags)) {
/* Copy credentials */
scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
unix_set_secdata(&scm, skb);
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2 changes: 2 additions & 0 deletions tools/include/uapi/asm-generic/socket.h
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Original file line number Diff line number Diff line change
Expand Up @@ -121,6 +121,8 @@

#define SO_RCVMARK 75

#define SO_PASSPIDFD 76

#if !defined(__KERNEL__)

#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
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