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Merge patch series "allow to create pidfds for reaped tasks with SCM_PIDFD"

Browse Source 
This is a logical continuation of the earlier work to create pidfds for
reaped tasks through the SO_PEERPIDFD socket option merged in
923ea4d448 ("Merge patch series "net, pidfs: enable handing out pidfds
for reaped sk->sk_peer_pid"").

* patches from https://lore.kernel.org/20250703222314.309967-1-aleksandr.mikhalitsyn@canonical.com:
  selftests: net: extend SCM_PIDFD test to cover stale pidfds
  af_unix: enable handing out pidfds for reaped tasks in SCM_PIDFD
  af_unix: stash pidfs dentry when needed
  af_unix/scm: fix whitespace errors
  af_unix: introduce and use scm_replace_pid() helper
  af_unix: introduce unix_skb_to_scm helper
  af_unix: rework unix_maybe_add_creds() to allow sleep

Link: https://lore.kernel.org/20250703222314.309967-1-aleksandr.mikhalitsyn@canonical.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-07-04 09:32:42 +02:00
commit 7a5b467e5d
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
4 changed files with 249 additions and 65 deletions
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32
net/core/scm.c
View File

@ -23,6 +23,8 @@
#include <linux/security.h>
#include <linux/pid_namespace.h>
#include <linux/pid.h>
#include <uapi/linux/pidfd.h>
#include <linux/pidfs.h>
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/errqueue.h>
@ -145,6 +147,22 @@ void __scm_destroy(struct scm_cookie *scm)
}
EXPORT_SYMBOL(__scm_destroy);
static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
{
int err;
/* drop all previous references */
scm_destroy_cred(scm);
err = pidfs_register_pid(pid);
if (unlikely(err))
return err;
scm->pid = pid;
scm->creds.pid = pid_vnr(pid);
return 0;
}
int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
{
const struct proto_ops *ops = READ_ONCE(sock->ops);
@ -189,15 +207,21 @@ int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
if (err)
goto error;
p->creds.pid = creds.pid;
if (!p->pid || pid_vnr(p->pid) != creds.pid) {
struct pid *pid;
err = -ESRCH;
pid = find_get_pid(creds.pid);
if (!pid)
goto error;
put_pid(p->pid);
p->pid = pid;
/* pass a struct pid reference from
* find_get_pid() to scm_replace_pid().
*/
err = scm_replace_pid(p, pid);
if (err) {
put_pid(pid);
goto error;
}
}
err = -EINVAL;
@ -459,7 +483,7 @@ static 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, PIDFD_STALE, &pidfd_file);
if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
if (pidfd_file) {

53
net/unix/af_unix.c
View File

@ -1955,21 +1955,45 @@ static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool sen
return err;
}
/*
static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
{
scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
unix_set_secdata(scm, skb);
}
/**
* unix_maybe_add_creds() - Adds current task uid/gid and struct pid to skb if needed.
* @skb: skb to attach creds to.
* @sk: Sender sock.
* @other: Receiver sock.
*
* Some apps rely on write() giving SCM_CREDENTIALS
* We include credentials if source or destination socket
* asserted SOCK_PASSCRED.
*
* Context: May sleep.
* Return: On success zero, on error a negative error code is returned.
*/
static void unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
const struct sock *other)
{
if (UNIXCB(skb).pid)
return;
return 0;
if (unix_may_passcred(sk) || unix_may_passcred(other)) {
UNIXCB(skb).pid = get_pid(task_tgid(current));
struct pid *pid;
int err;
pid = task_tgid(current);
err = pidfs_register_pid(pid);
if (unlikely(err))
return err;
UNIXCB(skb).pid = get_pid(pid);
current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
}
return 0;
}
static bool unix_skb_scm_eq(struct sk_buff *skb,
@ -2104,6 +2128,10 @@ lookup:
goto out_sock_put;
}
err = unix_maybe_add_creds(skb, sk, other);
if (err)
goto out_sock_put;
restart:
sk_locked = 0;
unix_state_lock(other);
@ -2212,7 +2240,6 @@ restart_locked:
if (sock_flag(other, SOCK_RCVTSTAMP))
__net_timestamp(skb);
unix_maybe_add_creds(skb, sk, other);
scm_stat_add(other, skb);
skb_queue_tail(&other->sk_receive_queue, skb);
unix_state_unlock(other);
@ -2256,6 +2283,10 @@ static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,
if (err < 0)
goto out;
err = unix_maybe_add_creds(skb, sk, other);
if (err)
goto out;
skb_put(skb, 1);
err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);
@ -2275,7 +2306,6 @@ static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,
goto out_unlock;
}
unix_maybe_add_creds(skb, sk, other);
scm_stat_add(other, skb);
spin_lock(&other->sk_receive_queue.lock);
@ -2369,6 +2399,10 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
fds_sent = true;
err = unix_maybe_add_creds(skb, sk, other);
if (err)
goto out_free;
if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
skb->ip_summed = CHECKSUM_UNNECESSARY;
err = skb_splice_from_iter(skb, &msg->msg_iter, size,
@ -2399,7 +2433,6 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
goto out_free;
}
unix_maybe_add_creds(skb, sk, other);
scm_stat_add(other, skb);
skb_queue_tail(&other->sk_receive_queue, skb);
unix_state_unlock(other);
@ -2547,8 +2580,7 @@ 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);
unix_set_secdata(&scm, skb);
unix_skb_to_scm(skb, &scm);
if (!(flags & MSG_PEEK)) {
if (UNIXCB(skb).fp)
@ -2933,8 +2965,7 @@ unlock:
break;
} else if (unix_may_passcred(sk)) {
/* Copy credentials */
scm_set_cred(&scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
unix_set_secdata(&scm, skb);
unix_skb_to_scm(skb, &scm);
check_creds = true;
}

221
tools/testing/selftests/net/af_unix/scm_pidfd.c
View File

@ -15,6 +15,7 @@
#include <sys/types.h>
#include <sys/wait.h>
#include "../../pidfd/pidfd.h"
#include "../../kselftest_harness.h"
#define clean_errno() (errno == 0 ? "None" : strerror(errno))
@ -26,6 +27,8 @@
#define SCM_PIDFD 0x04
#endif
#define CHILD_EXIT_CODE_OK 123
static void child_die()
{
exit(1);
@ -126,16 +129,65 @@ out:
return result;
}
struct cmsg_data {
struct ucred *ucred;
int *pidfd;
};
static int parse_cmsg(struct msghdr *msg, struct cmsg_data *res)
{
struct cmsghdr *cmsg;
int data = 0;
if (msg->msg_flags & (MSG_TRUNC | MSG_CTRUNC)) {
log_err("recvmsg: truncated");
return 1;
}
for (cmsg = CMSG_FIRSTHDR(msg); cmsg != NULL;
cmsg = CMSG_NXTHDR(msg, cmsg)) {
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_PIDFD) {
if (cmsg->cmsg_len < sizeof(*res->pidfd)) {
log_err("CMSG parse: SCM_PIDFD wrong len");
return 1;
}
res->pidfd = (void *)CMSG_DATA(cmsg);
}
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_CREDENTIALS) {
if (cmsg->cmsg_len < sizeof(*res->ucred)) {
log_err("CMSG parse: SCM_CREDENTIALS wrong len");
return 1;
}
res->ucred = (void *)CMSG_DATA(cmsg);
}
}
if (!res->pidfd) {
log_err("CMSG parse: SCM_PIDFD not found");
return 1;
}
if (!res->ucred) {
log_err("CMSG parse: SCM_CREDENTIALS not found");
return 1;
}
return 0;
}
static int cmsg_check(int fd)
{
struct msghdr msg = { 0 };
struct cmsghdr *cmsg;
struct cmsg_data res;
struct iovec iov;
struct ucred *ucred = NULL;
int data = 0;
char control[CMSG_SPACE(sizeof(struct ucred)) +
CMSG_SPACE(sizeof(int))] = { 0 };
int *pidfd = NULL;
pid_t parent_pid;
int err;
@ -158,53 +210,99 @@ static int cmsg_check(int fd)
return 1;
}
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
cmsg = CMSG_NXTHDR(&msg, cmsg)) {
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_PIDFD) {
if (cmsg->cmsg_len < sizeof(*pidfd)) {
log_err("CMSG parse: SCM_PIDFD wrong len");
return 1;
}
pidfd = (void *)CMSG_DATA(cmsg);
}
if (cmsg->cmsg_level == SOL_SOCKET &&
cmsg->cmsg_type == SCM_CREDENTIALS) {
if (cmsg->cmsg_len < sizeof(*ucred)) {
log_err("CMSG parse: SCM_CREDENTIALS wrong len");
return 1;
}
ucred = (void *)CMSG_DATA(cmsg);
}
}
/* send(pfd, "x", sizeof(char), 0) */
if (data != 'x') {
log_err("recvmsg: data corruption");
return 1;
}
if (!pidfd) {
log_err("CMSG parse: SCM_PIDFD not found");
return 1;
}
if (!ucred) {
log_err("CMSG parse: SCM_CREDENTIALS not found");
if (parse_cmsg(&msg, &res)) {
log_err("CMSG parse: parse_cmsg() failed");
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);
get_pid_from_fdinfo_file(*res.pidfd, "Pid:", sizeof("Pid:") - 1);
if (parent_pid != getppid()) {
log_err("wrong SCM_PIDFD %d != %d", parent_pid, getppid());
close(*res.pidfd);
return 1;
}
close(*res.pidfd);
return 0;
}
static int cmsg_check_dead(int fd, int expected_pid)
{
int err;
struct msghdr msg = { 0 };
struct cmsg_data res;
struct iovec iov;
int data = 0;
char control[CMSG_SPACE(sizeof(struct ucred)) +
CMSG_SPACE(sizeof(int))] = { 0 };
pid_t client_pid;
struct pidfd_info info = {
.mask = PIDFD_INFO_EXIT,
};
iov.iov_base = &data;
iov.iov_len = sizeof(data);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = control;
msg.msg_controllen = sizeof(control);
err = recvmsg(fd, &msg, 0);
if (err < 0) {
log_err("recvmsg");
return 1;
}
if (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC)) {
log_err("recvmsg: truncated");
return 1;
}
/* send(cfd, "y", sizeof(char), 0) */
if (data != 'y') {
log_err("recvmsg: data corruption");
return 1;
}
if (parse_cmsg(&msg, &res)) {
log_err("CMSG parse: parse_cmsg() failed");
return 1;
}
/*
* pidfd from SCM_PIDFD should point to the client_pid.
* Let's read exit information and check if it's what
* we expect to see.
*/
if (ioctl(*res.pidfd, PIDFD_GET_INFO, &info)) {
log_err("%s: ioctl(PIDFD_GET_INFO) failed", __func__);
close(*res.pidfd);
return 1;
}
if (!(info.mask & PIDFD_INFO_EXIT)) {
log_err("%s: No exit information from ioctl(PIDFD_GET_INFO)", __func__);
close(*res.pidfd);
return 1;
}
err = WIFEXITED(info.exit_code) ? WEXITSTATUS(info.exit_code) : 1;
if (err != CHILD_EXIT_CODE_OK) {
log_err("%s: wrong exit_code %d != %d", __func__, err, CHILD_EXIT_CODE_OK);
close(*res.pidfd);
return 1;
}
close(*res.pidfd);
return 0;
}
@ -291,6 +389,24 @@ static void fill_sockaddr(struct sock_addr *addr, bool abstract)
memcpy(sun_path_buf, addr->sock_name, strlen(addr->sock_name));
}
static int sk_enable_cred_pass(int sk)
{
int on = 0;
on = 1;
if (setsockopt(sk, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
log_err("Failed to set SO_PASSCRED");
return 1;
}
if (setsockopt(sk, SOL_SOCKET, SO_PASSPIDFD, &on, sizeof(on))) {
log_err("Failed to set SO_PASSPIDFD");
return 1;
}
return 0;
}
static void client(FIXTURE_DATA(scm_pidfd) *self,
const FIXTURE_VARIANT(scm_pidfd) *variant)
{
@ -299,7 +415,6 @@ static void client(FIXTURE_DATA(scm_pidfd) *self,
struct ucred peer_cred;
int peer_pidfd;
pid_t peer_pid;
int on = 0;
cfd = socket(AF_UNIX, variant->type, 0);
if (cfd < 0) {
@ -322,14 +437,8 @@ static void client(FIXTURE_DATA(scm_pidfd) *self,
child_die();
}
on = 1;
if (setsockopt(cfd, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
log_err("Failed to set SO_PASSCRED");
child_die();
}
if (setsockopt(cfd, SOL_SOCKET, SO_PASSPIDFD, &on, sizeof(on))) {
log_err("Failed to set SO_PASSPIDFD");
if (sk_enable_cred_pass(cfd)) {
log_err("sk_enable_cred_pass() failed");
child_die();
}
@ -340,6 +449,12 @@ static void client(FIXTURE_DATA(scm_pidfd) *self,
child_die();
}
/* send something to the parent so it can receive SCM_PIDFD too and validate it */
if (send(cfd, "y", sizeof(char), 0) == -1) {
log_err("Failed to send(cfd, \"y\", sizeof(char), 0)");
child_die();
}
/* skip further for SOCK_DGRAM as it's not applicable */
if (variant->type == SOCK_DGRAM)
return;
@ -398,7 +513,13 @@ TEST_F(scm_pidfd, test)
close(self->server);
close(self->startup_pipe[0]);
client(self, variant);
exit(0);
/*
* It's a bit unusual, but in case of success we return non-zero
* exit code (CHILD_EXIT_CODE_OK) and then we expect to read it
* from ioctl(PIDFD_GET_INFO) in cmsg_check_dead().
*/
exit(CHILD_EXIT_CODE_OK);
}
close(self->startup_pipe[1]);
@ -421,9 +542,17 @@ TEST_F(scm_pidfd, test)
ASSERT_NE(-1, err);
}
close(pfd);
waitpid(self->client_pid, &child_status, 0);
ASSERT_EQ(0, WIFEXITED(child_status) ? WEXITSTATUS(child_status) : 1);
/* see comment before exit(CHILD_EXIT_CODE_OK) */
ASSERT_EQ(CHILD_EXIT_CODE_OK, WIFEXITED(child_status) ? WEXITSTATUS(child_status) : 1);
err = sk_enable_cred_pass(pfd);
ASSERT_EQ(0, err);
err = cmsg_check_dead(pfd, self->client_pid);
ASSERT_EQ(0, err);
close(pfd);
}
TEST_HARNESS_MAIN