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SCM_PIDFD example
Raw
recv.c
/* This code is based on Michael Kerrisk examples from:
* https://man7.org/tlpi/code/online/dist/sockets/scm_cred_recv.c.html
*
* That's a proposal API for a new SCM_PIDFD auxiliary socket message
*
* Reference https://github.com/uapi-group/kernel-features
*/
/*************************************************************************\
* Copyright (C) Michael Kerrisk, 2022. *
* *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the *
* Free Software Foundation, either version 3 or (at your option) any *
* later version. This program is distributed without any warranty. See *
* the file COPYING.gpl-v3 for details. *
\*************************************************************************/
/* Supplementary program for Chapter 61 */
/* scm_cred_recv.c
Used in conjunction with scm_cred_send.c to demonstrate passing of
process credentials via a UNIX domain socket.
This program receives credentials sent to a UNIX domain socket.
Usage is as shown in the usageErr() call below.
Credentials can be exchanged over stream or datagram sockets. This program
uses stream sockets by default; the "-d" command-line option specifies
that datagram sockets should be used instead.
This program is Linux-specific.
See also scm_multi_recv.c.
*/
#include "scm_cred.h"
#define SO_PASSPIDFD 76
#define SCM_PIDFD 0x04 /* rw: pidfd (int) */
int
main(int argc, char *argv[])
{
/* Allocate a char array of suitable size to hold the ancillary data.
However, since this buffer is in reality a 'struct cmsghdr', use a
union to ensure that it is aligned as required for that structure.
Alternatively, we could allocate the buffer using malloc(), which
returns a buffer that satisfies the strictest alignment
requirements of any type */
union {
char buf[CMSG_SPACE(sizeof(struct ucred))+CMSG_SPACE(sizeof(int))];
/* Space large enough to hold a 'ucred' structure and pidfd */
struct cmsghdr align;
} controlMsg;
/* Parse command-line options */
bool useDatagramSocket = false;
int opt;
while ((opt = getopt(argc, argv, "d")) != -1) {
switch (opt) {
case 'd':
useDatagramSocket = true;
break;
default:
usageErr("%s [-d]\n"
" -d use datagram socket\n", argv[0]);
}
}
/* Create socket bound to a well-known address. In the case where
we are using stream sockets, also make the socket a listening
socket and accept a connection on the socket. */
if (remove(SOCK_PATH) == -1 && errno != ENOENT)
errExit("remove-%s", SOCK_PATH);
int sfd;
if (useDatagramSocket) {
sfd = unixBind(SOCK_PATH, SOCK_DGRAM);
if (sfd == -1)
errExit("unixBind");
} else {
int lfd = unixBind(SOCK_PATH, SOCK_STREAM);
if (lfd == -1)
errExit("unixBind");
if (listen(lfd, 5) == -1)
errExit("listen");
sfd = accept(lfd, NULL, NULL);
if (sfd == -1)
errExit("accept");
}
/* We must set the SO_PASSCRED socket option in order to receive
credentials */
int optval = 1;
if (setsockopt(sfd, SOL_SOCKET, SO_PASSCRED, &optval, sizeof(optval)) == -1)
errExit("setsockopt");
/* We must set the SO_PASSPIDFD socket option in order to receive
pidfd */
optval = 1;
if (setsockopt(sfd, SOL_SOCKET, SO_PASSPIDFD, &optval, sizeof(optval)) == -1)
errExit("setsockopt");
/* The 'msg_name' field can be set to point to a buffer where the
kernel will place the address of the peer socket. However, we don't
need the address of the peer, so we set this field to NULL. */
struct msghdr msgh;
msgh.msg_name = NULL;
msgh.msg_namelen = 0;
/* Set fields of 'msgh' to point to buffer used to receive (real)
data read by recvmsg() */
struct iovec iov;
int data;
msgh.msg_iov = &iov;
msgh.msg_iovlen = 1;
iov.iov_base = &data;
iov.iov_len = sizeof(data);
/* Set 'msgh' fields to describe the ancillary data buffer */
msgh.msg_control = controlMsg.buf;
msgh.msg_controllen = sizeof(controlMsg.buf);
/* Receive real plus ancillary data */
ssize_t nr = recvmsg(sfd, &msgh, 0);
if (nr == -1)
errExit("recvmsg");
printf("recvmsg() returned %zd\n", nr);
if (nr > 0)
printf("Received data = %d\n", data);
/* Get the address of the first 'cmsghdr' in the received
ancillary data */
struct cmsghdr *cmsgp = CMSG_FIRSTHDR(&msgh);
/* Check the validity of the 'cmsghdr' */
if (cmsgp == NULL || cmsgp->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
fatal("bad cmsg header / message length");
if (cmsgp->cmsg_level != SOL_SOCKET)
fatal("cmsg_level != SOL_SOCKET");
if (cmsgp->cmsg_type != SCM_CREDENTIALS)
fatal("cmsg_type != SCM_CREDENTIALS");
/* Copy the contents of the data field of the 'cmsghdr' to a
'struct ucred'. */
struct ucred rcred;
memcpy(&rcred, CMSG_DATA(cmsgp), sizeof(struct ucred));
/* Display the credentials from the received data area */
printf("Received credentials pid=%ld, uid=%ld, gid=%ld\n",
(long) rcred.pid, (long) rcred.uid, (long) rcred.gid);
cmsgp = CMSG_NXTHDR(&msgh, cmsgp);
if (cmsgp == NULL || cmsgp->cmsg_len != CMSG_LEN(sizeof(int)))
fatal("bad cmsg header / message length");
if (cmsgp->cmsg_level != SOL_SOCKET)
fatal("cmsg_level != SOL_SOCKET");
if (cmsgp->cmsg_type != SCM_PIDFD)
fatal("cmsg_type != SCM_PIDFD");
int pidfd;
memcpy(&pidfd, CMSG_DATA(cmsgp), sizeof(int));
printf("Received pidfd=%d\n",
pidfd);
char buf[100];
sprintf(buf, "cat /proc/%d/fdinfo/%d", getpid(), pidfd);
system(buf);
exit(EXIT_SUCCESS);
}
Raw
scm_pidfd.patch
From fbc6eb4f12d87dd3e3e36af3fd49ca1f30a7d04e Mon Sep 17 00:00:00 2001
From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Date: Sun, 26 Feb 2023 23:04:18 +0100
Subject: [PATCH] scm: add SO_PASSPIDFD and SCM_PIDFD
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
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..1aa0130b812b 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 /* rw: 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 ||
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))
+ pidfd = -ESRCH;
+ else
+ 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);
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 638230899e98..b76169fdb80b 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -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__))
diff --git a/net/core/sock.c b/net/core/sock.c
index 341c565dbc26..255d29dec4d6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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:
@@ -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;
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 8a9656248b0f..bd80e707d0b3 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -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:
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 347122c3575e..45ab9264c0ba 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -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)
@@ -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;
@@ -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);
}
@@ -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);
}
/*
@@ -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;
@@ -2818,7 +2825,8 @@ 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);
diff --git a/tools/include/uapi/asm-generic/socket.h b/tools/include/uapi/asm-generic/socket.h
index 8756df13be50..fbbc4bf53ee3 100644
--- a/tools/include/uapi/asm-generic/socket.h
+++ b/tools/include/uapi/asm-generic/socket.h
@@ -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__))
--
2.34.1
Raw
send.c
/* This code is based on Michael Kerrisk examples from:
* https://man7.org/tlpi/code/online/dist/sockets/scm_cred_recv.c.html
*
* That's a proposal API for a new SCM_PIDFD auxiliary socket message
*
* Reference https://github.com/uapi-group/kernel-features
*/
/*************************************************************************\
* Copyright (C) Michael Kerrisk, 2022. *
* *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the *
* Free Software Foundation, either version 3 or (at your option) any *
* later version. This program is distributed without any warranty. See *
* the file COPYING.gpl-v3 for details. *
\*************************************************************************/
/* Supplementary program for Chapter 61 */
/* scm_cred_send.c
Used in conjunction with scm_cred_recv.c to demonstrate passing of
process credentials via a UNIX domain socket.
This program sends credentials to a UNIX domain socket.
Usage is as shown in the usageErr() call below.
Credentials can be exchanged over stream or datagram sockets. This program
uses stream sockets by default; the "-d" command-line option specifies
that datagram sockets should be used instead.
This program is Linux-specific.
See also scm_multi_send.c.
*/
#include "scm_cred.h"
#define SO_PASSPIDFD 76
#define SCM_PIDFD 0x04 /* rw: pidfd (int) */
int
main(int argc, char *argv[])
{
/* Allocate a char array of suitable size to hold the ancillary data.
However, since this buffer is in reality a 'struct cmsghdr', use a
union to ensure that it is aligned as required for that structure.
Alternatively, we could allocate the buffer using malloc(), which
returns a buffer that satisfies the strictest alignment
requirements of any type */
union {
char buf[CMSG_SPACE(sizeof(struct ucred))];
/* Space large enough to hold a ucred structure */
struct cmsghdr align;
} controlMsg;
/* Parse command-line options */
bool useDatagramSocket = false;
bool noExplicitCreds = false;
int opt;
while ((opt = getopt(argc, argv, "dn")) != -1) {
switch (opt) {
case 'd':
useDatagramSocket = true;
break;
case 'n':
noExplicitCreds = true;
break;
default:
usageErr("%s [-d] [-n] [data [PID [UID [GID]]]]\n"
" -d use datagram socket\n"
" -n don't construct explicit "
"credentials structure\n", argv[0]);
}
}
/* The 'msg_name' field can be used to specify the address of the
destination socket when sending a datagram. However, we do not
need to use this field because we use connect() below, which sets
a default outgoing address for datagrams. */
struct msghdr msgh;
msgh.msg_name = NULL;
msgh.msg_namelen = 0;
/* On Linux, we must transmit at least 1 byte of real data in
order to send ancillary data */
int data = (argc > optind) ? atoi(argv[optind]) : 12345;
/* Data is optionally taken from command line */
fprintf(stderr, "Sending data = %d\n", data);
struct iovec iov;
msgh.msg_iov = &iov;
msgh.msg_iovlen = 1;
iov.iov_base = &data;
iov.iov_len = sizeof(data);
if (noExplicitCreds) {
/* Don't construct an explicit credentials structure. (It is not
necessary to do so, if we just want the receiver to receive
our real credentials.) */
printf("Not explicitly sending a credentials structure\n");
msgh.msg_control = NULL;
msgh.msg_controllen = 0;
} else {
/* Set 'msgh' fields to describe the ancillary data buffer */
msgh.msg_control = controlMsg.buf;
msgh.msg_controllen = sizeof(controlMsg.buf);
/* The control message buffer must be zero-initialized in order for the
CMSG_NXTHDR() macro to work correctly. Although we don't need to use
CMSG_NXTHDR() in this example (because there is only one block of
ancillary data), we show this step to demonstrate best practice */
memset(controlMsg.buf, 0, sizeof(controlMsg.buf));
/* Set message header to describe the ancillary data that
we want to send */
struct cmsghdr *cmsgp = CMSG_FIRSTHDR(&msgh);
cmsgp->cmsg_len = CMSG_LEN(sizeof(struct ucred));
cmsgp->cmsg_level = SOL_SOCKET;
cmsgp->cmsg_type = SCM_CREDENTIALS;
/* Use sender's own PID, real UID, and real GID, unless
alternate values were supplied on the command line */
struct ucred creds;
creds.pid = getpid();
if (argc > optind + 1 && strcmp(argv[optind + 1], "-") != 0)
creds.pid = atoi(argv[optind + 1]);
creds.uid = getuid();
if (argc > optind + 2 && strcmp(argv[optind + 2], "-") != 0)
creds.uid = atoi(argv[optind + 2]);
creds.gid = getgid();
if (argc > optind + 3 && strcmp(argv[optind + 3], "-") != 0)
creds.gid = atoi(argv[optind + 3]);
printf("Send credentials pid=%ld, uid=%ld, gid=%ld\n",
(long) creds.pid, (long) creds.uid, (long) creds.gid);
/* Copy 'ucred' structure into data field in the 'cmsghdr' */
memcpy(CMSG_DATA(cmsgp), &creds, sizeof(struct ucred));
}
/* Connect to the peer socket */
int sfd = unixConnect(SOCK_PATH,
useDatagramSocket ? SOCK_DGRAM : SOCK_STREAM);
if (sfd == -1)
errExit("unixConnect");
/* Send real plus ancillary data */
ssize_t ns = sendmsg(sfd, &msgh, 0);
if (ns == -1)
errExit("sendmsg");
printf("sendmsg() returned %zd\n", ns);
sleep(100);
exit(EXIT_SUCCESS);
}
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