linux-stable/include/net/scm.h
Alexander Mikhalitsyn a9c49cc2f5 net: scm: introduce and use scm_recv_unix helper
Recently, our friends from bluetooth subsystem reported [1] that after
commit 5e2ff6704a ("scm: add SO_PASSPIDFD and SCM_PIDFD") scm_recv()
helper become unusable in kernel modules (because it uses unexported
pidfd_prepare() API).

We were aware of this issue and workarounded it in a hard way
by commit 97154bcf4d ("af_unix: Kconfig: make CONFIG_UNIX bool").

But recently a new functionality was added in the scope of commit
817efd3cad74 ("Bluetooth: hci_sock: Forward credentials to monitor")
and after that bluetooth can't be compiled as a kernel module.

After some discussion in [1] we decided to split scm_recv() into
two helpers, one won't support SCM_PIDFD (used for unix sockets),
and another one will be completely the same as it was before commit
5e2ff6704a ("scm: add SO_PASSPIDFD and SCM_PIDFD").

Link: https://lore.kernel.org/lkml/CAJqdLrpFcga4n7wxBhsFqPQiN8PKFVr6U10fKcJ9W7AcZn+o6Q@mail.gmail.com/ [1]
Fixes: 5e2ff6704a ("scm: add SO_PASSPIDFD and SCM_PIDFD")
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230627174314.67688-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2023-06-27 10:50:22 -07:00

208 lines
4.9 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_NET_SCM_H
#define __LINUX_NET_SCM_H
#include <linux/limits.h>
#include <linux/net.h>
#include <linux/cred.h>
#include <linux/security.h>
#include <linux/pid.h>
#include <linux/nsproxy.h>
#include <linux/sched/signal.h>
/* Well, we should have at least one descriptor open
* to accept passed FDs 8)
*/
#define SCM_MAX_FD 253
struct scm_creds {
u32 pid;
kuid_t uid;
kgid_t gid;
};
struct scm_fp_list {
short count;
short max;
struct user_struct *user;
struct file *fp[SCM_MAX_FD];
};
struct scm_cookie {
struct pid *pid; /* Skb credentials */
struct scm_fp_list *fp; /* Passed files */
struct scm_creds creds; /* Skb credentials */
#ifdef CONFIG_SECURITY_NETWORK
u32 secid; /* Passed security ID */
#endif
};
void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm);
void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm);
int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm);
void __scm_destroy(struct scm_cookie *scm);
struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl);
#ifdef CONFIG_SECURITY_NETWORK
static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
{
security_socket_getpeersec_dgram(sock, NULL, &scm->secid);
}
#else
static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm)
{ }
#endif /* CONFIG_SECURITY_NETWORK */
static __inline__ void scm_set_cred(struct scm_cookie *scm,
struct pid *pid, kuid_t uid, kgid_t gid)
{
scm->pid = get_pid(pid);
scm->creds.pid = pid_vnr(pid);
scm->creds.uid = uid;
scm->creds.gid = gid;
}
static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
{
put_pid(scm->pid);
scm->pid = NULL;
}
static __inline__ void scm_destroy(struct scm_cookie *scm)
{
scm_destroy_cred(scm);
if (scm->fp)
__scm_destroy(scm);
}
static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm, bool forcecreds)
{
memset(scm, 0, sizeof(*scm));
scm->creds.uid = INVALID_UID;
scm->creds.gid = INVALID_GID;
if (forcecreds)
scm_set_cred(scm, task_tgid(current), current_uid(), current_gid());
unix_get_peersec_dgram(sock, scm);
if (msg->msg_controllen <= 0)
return 0;
return __scm_send(sock, msg, scm);
}
#ifdef CONFIG_SECURITY_NETWORK
static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
{
char *secdata;
u32 seclen;
int err;
if (test_bit(SOCK_PASSSEC, &sock->flags)) {
err = security_secid_to_secctx(scm->secid, &secdata, &seclen);
if (!err) {
put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, seclen, secdata);
security_release_secctx(secdata, seclen);
}
}
}
static inline bool scm_has_secdata(struct socket *sock)
{
return test_bit(SOCK_PASSSEC, &sock->flags);
}
#else
static inline void scm_passec(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm)
{ }
static inline bool scm_has_secdata(struct socket *sock)
{
return false;
}
#endif /* CONFIG_SECURITY_NETWORK */
static __inline__ void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
{
struct file *pidfd_file = NULL;
int pidfd;
/*
* put_cmsg() doesn't return an error if CMSG is truncated,
* that's why we need to opencode these checks here.
*/
if ((msg->msg_controllen <= sizeof(struct cmsghdr)) ||
(msg->msg_controllen - sizeof(struct cmsghdr)) < sizeof(int)) {
msg->msg_flags |= MSG_CTRUNC;
return;
}
if (!scm->pid)
return;
pidfd = pidfd_prepare(scm->pid, 0, &pidfd_file);
if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
if (pidfd_file) {
put_unused_fd(pidfd);
fput(pidfd_file);
}
return;
}
if (pidfd_file)
fd_install(pidfd, pidfd_file);
}
static inline bool __scm_recv_common(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm, int flags)
{
if (!msg->msg_control) {
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 false;
}
if (test_bit(SOCK_PASSCRED, &sock->flags)) {
struct user_namespace *current_ns = current_user_ns();
struct ucred ucreds = {
.pid = scm->creds.pid,
.uid = from_kuid_munged(current_ns, scm->creds.uid),
.gid = from_kgid_munged(current_ns, scm->creds.gid),
};
put_cmsg(msg, SOL_SOCKET, SCM_CREDENTIALS, sizeof(ucreds), &ucreds);
}
scm_passec(sock, msg, scm);
if (scm->fp)
scm_detach_fds(msg, scm);
return true;
}
static inline void scm_recv(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm, int flags)
{
if (!__scm_recv_common(sock, msg, scm, flags))
return;
scm_destroy_cred(scm);
}
static inline void scm_recv_unix(struct socket *sock, struct msghdr *msg,
struct scm_cookie *scm, int flags)
{
if (!__scm_recv_common(sock, msg, scm, flags))
return;
if (test_bit(SOCK_PASSPIDFD, &sock->flags))
scm_pidfd_recv(msg, scm);
scm_destroy_cred(scm);
}
#endif /* __LINUX_NET_SCM_H */