Currently SCM_PIDFD cmsg cannot be sent via unix socket (returns -EINVAL) and SO_PASSPIDFD doesn't support flags. The created pidfd always has flags set to 0.

This patch implements SCM_PIDFD cmsg in AF_UNIX socket, which can be used to send flags to SO_PASSPIDFD-enabled recipient.

Self-test is added for the propagation of PIDFD_NONBLOCK flag.

This is mainly needed for the future extensions, like eg this one: https://lore.kernel.org/lkml/8288a08e-448b-43c2-82dc-59f87d0d9072@yandex.ru/... where it was suggested to try solving the supplementary groups problem with pidfd.

Changes in v2: remove flags validation in scm_pidfd_recv(), as suggested by Kuniyuki Iwashima kuniyu@amazon.com

Signed-off-by: Stas Sergeev stsp2@yandex.ru

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: Simon Horman horms@kernel.org CC: Shuah Khan shuah@kernel.org CC: Christian Brauner brauner@kernel.org CC: Jens Axboe axboe@kernel.dk CC: Willem de Bruijn willemb@google.com CC: Pavel Begunkov asml.silence@gmail.com CC: Gabriel Krisman Bertazi krisman@suse.de CC: Mina Almasry almasrymina@google.com CC: Oleg Nesterov oleg@redhat.com CC: Tycho Andersen tandersen@netflix.com CC: Al Viro viro@zeniv.linux.org.uk CC: Kuniyuki Iwashima kuniyu@amazon.com CC: Gou Hao gouhao@uniontech.com CC: Abhishek Chauhan quic_abchauha@quicinc.com CC: Michal Luczaj mhal@rbox.co CC: Kees Cook kees@kernel.org CC: Aleksa Sarai cyphar@cyphar.com CC: linux-kernel@vger.kernel.org CC: netdev@vger.kernel.org CC: linux-kselftest@vger.kernel.org --- include/linux/pidfs.h | 9 +++ include/linux/socket.h | 2 +- include/net/af_unix.h | 1 + include/net/scm.h | 3 +- kernel/pid.c | 6 +- net/core/scm.c | 14 ++++ net/core/sock.c | 1 + net/unix/af_unix.c | 3 + .../testing/selftests/net/af_unix/scm_pidfd.c | 70 +++++++++++++++++-- 9 files changed, 99 insertions(+), 10 deletions(-)

diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h index 75bdf9807802..c4c5c1a0c2ad 100644 --- a/include/linux/pidfs.h +++ b/include/linux/pidfs.h @@ -2,7 +2,16 @@ #ifndef _LINUX_PID_FS_H #define _LINUX_PID_FS_H

+#include <uapi/linux/pidfd.h> + struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags); void __init pidfs_init(void);

+static inline int pidfd_validate_flags(unsigned int flags) +{ + if (flags & ~(PIDFD_NONBLOCK | PIDFD_THREAD)) + return -EINVAL; + return 0; +} + #endif /* _LINUX_PID_FS_H */ diff --git a/include/linux/socket.h b/include/linux/socket.h index d18cc47e89bd..ee27d391e5aa 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -178,7 +178,7 @@ 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) */ +#define SCM_PIDFD 0x04 /* r: pidfd, w: pidfd_flags (int) */

struct ucred { __u32 pid; diff --git a/include/net/af_unix.h b/include/net/af_unix.h index 63129c79b8cb..4bc197548c2f 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -62,6 +62,7 @@ struct unix_skb_parms { #ifdef CONFIG_SECURITY_NETWORK u32 secid; /* Security ID */ #endif + u32 pidfd_flags; u32 consumed; } __randomize_layout;

diff --git a/include/net/scm.h b/include/net/scm.h index 0d35c7c77a74..1326edcacacb 100644 --- a/include/net/scm.h +++ b/include/net/scm.h @@ -48,6 +48,7 @@ struct scm_cookie { #ifdef CONFIG_SECURITY_NETWORK u32 secid; /* Passed security ID */ #endif + u32 pidfd_flags; };

void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm); @@ -154,7 +155,7 @@ static __inline__ void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm if (!scm->pid) return;

- pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file); + pidfd = pidfd_prepare(scm->pid, scm->pidfd_flags, &pidfd_file);

if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) { if (pidfd_file) { diff --git a/kernel/pid.c b/kernel/pid.c index 2715afb77eab..b1100ae8ea63 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -629,10 +629,12 @@ static int pidfd_create(struct pid *pid, unsigned int flags) SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) { int fd; + int err; struct pid *p;

- if (flags & ~(PIDFD_NONBLOCK | PIDFD_THREAD)) - return -EINVAL; + err = pidfd_validate_flags(flags); + if (err) + return err;

if (pid <= 0) return -EINVAL; diff --git a/net/core/scm.c b/net/core/scm.c index 4f6a14babe5a..3bcdecdacd7e 100644 --- a/net/core/scm.c +++ b/net/core/scm.c @@ -23,6 +23,7 @@ #include <linux/security.h> #include <linux/pid_namespace.h> #include <linux/pid.h> +#include <linux/pidfs.h> #include <linux/nsproxy.h> #include <linux/slab.h> #include <linux/errqueue.h> @@ -210,6 +211,19 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p) p->creds.gid = gid; break; } + case SCM_PIDFD: + { + unsigned int flags; + + if (cmsg->cmsg_len != CMSG_LEN(sizeof(flags))) + goto error; + memcpy(&flags, CMSG_DATA(cmsg), sizeof(flags)); + err = pidfd_validate_flags(flags); + if (err) + goto error; + p->pidfd_flags = flags; + break; + } default: goto error; } diff --git a/net/core/sock.c b/net/core/sock.c index 039be95c40cf..d1fce437c035 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -2930,6 +2930,7 @@ int __sock_cmsg_send(struct sock *sk, struct cmsghdr *cmsg, /* SCM_RIGHTS and SCM_CREDENTIALS are semantically in SOL_UNIX. */ case SCM_RIGHTS: case SCM_CREDENTIALS: + case SCM_PIDFD: break; default: return -EINVAL; diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 001ccc55ef0f..8b19dfec0221 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1892,6 +1892,7 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen UNIXCB(skb).uid = scm->creds.uid; UNIXCB(skb).gid = scm->creds.gid; UNIXCB(skb).fp = NULL; + UNIXCB(skb).pidfd_flags = scm->pidfd_flags; unix_get_secdata(scm, skb); if (scm->fp && send_fds) err = unix_attach_fds(scm, skb); @@ -2486,6 +2487,7 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size, memset(&scm, 0, sizeof(scm));

scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid); + scm.pidfd_flags = UNIXCB(skb).pidfd_flags; unix_set_secdata(&scm, skb);

if (!(flags & MSG_PEEK)) { @@ -2873,6 +2875,7 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state, test_bit(SOCK_PASSPIDFD, &sock->flags)) { /* Copy credentials */ scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid); + scm.pidfd_flags = UNIXCB(skb).pidfd_flags; unix_set_secdata(&scm, skb); check_creds = true; } diff --git a/tools/testing/selftests/net/af_unix/scm_pidfd.c b/tools/testing/selftests/net/af_unix/scm_pidfd.c index 7e534594167e..1e70ff253a1d 100644 --- a/tools/testing/selftests/net/af_unix/scm_pidfd.c +++ b/tools/testing/selftests/net/af_unix/scm_pidfd.c @@ -5,6 +5,7 @@ #include <stddef.h> #include <stdio.h> #include <stdlib.h> +#include <fcntl.h> #include <sys/socket.h> #include <linux/socket.h> #include <unistd.h> @@ -15,6 +16,11 @@ #include <sys/types.h> #include <sys/wait.h>

+/* There are problems including linux/pidfd.h, so define. */ +#ifndef PIDFD_NONBLOCK +#define PIDFD_NONBLOCK O_NONBLOCK +#endif + #include "../../kselftest_harness.h"

#define clean_errno() (errno == 0 ? "None" : strerror(errno)) @@ -126,7 +132,7 @@ static pid_t get_pid_from_fdinfo_file(int pidfd, const char *key, size_t keylen) return result; }

-static int cmsg_check(int fd) +static int cmsg_check(int fd, unsigned int pidfd_flags) { struct msghdr msg = { 0 }; struct cmsghdr *cmsg; @@ -136,6 +142,7 @@ static int cmsg_check(int fd) char control[CMSG_SPACE(sizeof(struct ucred)) + CMSG_SPACE(sizeof(int))] = { 0 }; int *pidfd = NULL; + unsigned int flags; pid_t parent_pid; int err;

@@ -197,6 +204,13 @@ static int cmsg_check(int fd) return 1; }

+ flags = fcntl(*pidfd, F_GETFL, 0); + flags &= ~O_ACCMODE; + if (flags != pidfd_flags) { + log_err("SCM_PIDFD flags mismatch: %x != %x", flags, pidfd_flags); + return 1; + } + /* pidfd from SCM_PIDFD should point to the parent process PID */ parent_pid = get_pid_from_fdinfo_file(*pidfd, "Pid:", sizeof("Pid:") - 1); @@ -227,30 +241,49 @@ FIXTURE_VARIANT(scm_pidfd) { int type; bool abstract; + unsigned int flags; };

FIXTURE_VARIANT_ADD(scm_pidfd, stream_pathname) { .type = SOCK_STREAM, .abstract = 0, + .flags = 0, };

FIXTURE_VARIANT_ADD(scm_pidfd, stream_abstract) { .type = SOCK_STREAM, .abstract = 1, + .flags = 0, };

FIXTURE_VARIANT_ADD(scm_pidfd, dgram_pathname) { .type = SOCK_DGRAM, .abstract = 0, + .flags = 0, };

FIXTURE_VARIANT_ADD(scm_pidfd, dgram_abstract) { .type = SOCK_DGRAM, .abstract = 1, + .flags = 0, +}; + +FIXTURE_VARIANT_ADD(scm_pidfd, stream_nonblock) +{ + .type = SOCK_STREAM, + .abstract = 0, + .flags = PIDFD_NONBLOCK, +}; + +FIXTURE_VARIANT_ADD(scm_pidfd, dgram_nonblock) +{ + .type = SOCK_DGRAM, + .abstract = 0, + .flags = PIDFD_NONBLOCK, };

FIXTURE_SETUP(scm_pidfd) @@ -335,7 +368,7 @@ static void client(FIXTURE_DATA(scm_pidfd) *self,

close(self->startup_pipe[1]);

- if (cmsg_check(cfd)) { + if (cmsg_check(cfd, variant->flags)) { log_err("cmsg_check failed"); child_die(); } @@ -375,6 +408,27 @@ TEST_F(scm_pidfd, test) int err; int pfd; int child_status = 0; + char iobuf; + unsigned int pidfd_flags; + struct msghdr msg = { 0 }; + struct cmsghdr *cmsg; + struct iovec io = { + .iov_base = &iobuf, + .iov_len = sizeof(iobuf) + }; + union { + char buf[CMSG_SPACE(sizeof(pidfd_flags))]; + struct cmsghdr align; + } u; + + msg.msg_iov = &io; + msg.msg_iovlen = 1; + msg.msg_control = u.buf; + msg.msg_controllen = sizeof(u.buf); + cmsg = CMSG_FIRSTHDR(&msg); + cmsg->cmsg_level = SOL_SOCKET; + cmsg->cmsg_type = SCM_PIDFD; + cmsg->cmsg_len = CMSG_LEN(sizeof(pidfd_flags));

self->server = socket(AF_UNIX, variant->type, 0); ASSERT_NE(-1, self->server); @@ -414,12 +468,16 @@ TEST_F(scm_pidfd, test) close(self->startup_pipe[0]);

if (variant->type == SOCK_DGRAM) { - err = sendto(pfd, "x", sizeof(char), 0, (struct sockaddr *)&self->client_addr->listen_addr, self->client_addr->addrlen); - ASSERT_NE(-1, err); - } else { - err = send(pfd, "x", sizeof(char), 0); + err = connect(pfd, + (struct sockaddr *)&self->client_addr->listen_addr, + self->client_addr->addrlen); ASSERT_NE(-1, err); } + iobuf = 'x'; + pidfd_flags = variant->flags; + memcpy(CMSG_DATA(cmsg), &pidfd_flags, sizeof(pidfd_flags)); + err = sendmsg(pfd, &msg, 0); + ASSERT_NE(-1, err);

close(pfd); waitpid(self->client_pid, &child_status, 0);