// SPDX-License-Identifier: GPL-2.0-or-later
/* scm.c - Socket level control messages processing.
 *
 * Author:      Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *              Alignment and value checking mods by Craig Metz
 */

#include <linux/module.h>
#include <linux/signal.h>
#include <linux/capability.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/stat.h>
#include <linux/socket.h>
#include <linux/file.h>
#include <linux/fcntl.h>
#include <linux/net.h>
#include <linux/interrupt.h>
#include <linux/netdevice.h>
#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>
#include <linux/io_uring.h>

#include <linux/uaccess.h>

#include <net/protocol.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/compat.h>
#include <net/scm.h>
#include <net/cls_cgroup.h>
#include <net/af_unix.h>


/*
 *      Only allow a user to send credentials, that they could set with
 *      setu(g)id.
 */

static __inline__ int scm_check_creds(struct ucred *creds)
{
        const struct cred *cred = current_cred();
        kuid_t uid = make_kuid(cred->user_ns, creds->uid);
        kgid_t gid = make_kgid(cred->user_ns, creds->gid);

        if (!uid_valid(uid) || !gid_valid(gid))
                return -EINVAL;

        if ((creds->pid == task_tgid_vnr(current) ||
             ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
            ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
              uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
            ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
              gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
               return 0;
        }
        return -EPERM;
}

static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
{
        int *fdp = (int*)CMSG_DATA(cmsg);
        struct scm_fp_list *fpl = *fplp;
        struct file **fpp;
        int i, num;

        num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);

        if (num <= 0)
                return 0;

        if (num > SCM_MAX_FD)
                return -EINVAL;

        if (!fpl)
        {
                fpl = kmalloc_obj(struct scm_fp_list, GFP_KERNEL_ACCOUNT);
                if (!fpl)
                        return -ENOMEM;
                *fplp = fpl;
                fpl->count = 0;
                fpl->count_unix = 0;
                fpl->max = SCM_MAX_FD;
                fpl->user = NULL;
#if IS_ENABLED(CONFIG_UNIX)
                fpl->inflight = false;
                fpl->dead = false;
                fpl->edges = NULL;
                INIT_LIST_HEAD(&fpl->vertices);
#endif
        }
        fpp = &fpl->fp[fpl->count];

        if (fpl->count + num > fpl->max)
                return -EINVAL;

        /*
         *      Verify the descriptors and increment the usage count.
         */

        for (i=0; i< num; i++)
        {
                int fd = fdp[i];
                struct file *file;

                if (fd < 0 || !(file = fget_raw(fd)))
                        return -EBADF;
                /* don't allow io_uring files */
                if (io_is_uring_fops(file)) {
                        fput(file);
                        return -EINVAL;
                }
                if (unix_get_socket(file))
                        fpl->count_unix++;

                *fpp++ = file;
                fpl->count++;
        }

        if (!fpl->user)
                fpl->user = get_uid(current_user());

        return num;
}

void __scm_destroy(struct scm_cookie *scm)
{
        struct scm_fp_list *fpl = scm->fp;
        int i;

        if (fpl) {
                scm->fp = NULL;
                for (i=fpl->count-1; i>=0; i--)
                        fput(fpl->fp[i]);
                free_uid(fpl->user);
                kfree(fpl);
        }
}
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);
        struct cmsghdr *cmsg;
        int err;

        for_each_cmsghdr(cmsg, msg) {
                err = -EINVAL;

                /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
                /* The first check was omitted in <= 2.2.5. The reasoning was
                   that parser checks cmsg_len in any case, so that
                   additional check would be work duplication.
                   But if cmsg_level is not SOL_SOCKET, we do not check
                   for too short ancillary data object at all! Oops.
                   OK, let's add it...
                 */
                if (!CMSG_OK(msg, cmsg))
                        goto error;

                if (cmsg->cmsg_level != SOL_SOCKET)
                        continue;

                switch (cmsg->cmsg_type)
                {
                case SCM_RIGHTS:
                        if (!ops || ops->family != PF_UNIX)
                                goto error;
                        err=scm_fp_copy(cmsg, &p->fp);
                        if (err<0)
                                goto error;
                        break;
                case SCM_CREDENTIALS:
                {
                        struct ucred creds;
                        kuid_t uid;
                        kgid_t gid;
                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
                                goto error;
                        memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
                        err = scm_check_creds(&creds);
                        if (err)
                                goto error;

                        if (!p->pid || pid_vnr(p->pid) != creds.pid) {
                                struct pid *pid;
                                err = -ESRCH;
                                pid = find_get_pid(creds.pid);
                                if (!pid)
                                        goto error;

                                /* 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;
                        uid = make_kuid(current_user_ns(), creds.uid);
                        gid = make_kgid(current_user_ns(), creds.gid);
                        if (!uid_valid(uid) || !gid_valid(gid))
                                goto error;

                        p->creds.uid = uid;
                        p->creds.gid = gid;
                        break;
                }
                default:
                        goto error;
                }
        }

        if (p->fp && !p->fp->count)
        {
                kfree(p->fp);
                p->fp = NULL;
        }
        return 0;

error:
        scm_destroy(p);
        return err;
}
EXPORT_SYMBOL(__scm_send);

int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
{
        int cmlen = CMSG_LEN(len);

        if (msg->msg_flags & MSG_CMSG_COMPAT)
                return put_cmsg_compat(msg, level, type, len, data);

        if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
                msg->msg_flags |= MSG_CTRUNC;
                return 0; /* XXX: return error? check spec. */
        }
        if (msg->msg_controllen < cmlen) {
                msg->msg_flags |= MSG_CTRUNC;
                cmlen = msg->msg_controllen;
        }

        if (msg->msg_control_is_user) {
                struct cmsghdr __user *cm = msg->msg_control_user;

                check_object_size(data, cmlen - sizeof(*cm), true);

                scoped_user_write_access_size(cm, cmlen, efault) {
                        unsafe_put_user(cmlen, &cm->cmsg_len, efault);
                        unsafe_put_user(level, &cm->cmsg_level, efault);
                        unsafe_put_user(type, &cm->cmsg_type, efault);
                        unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
                                            cmlen - sizeof(*cm), efault);
                }
        } else {
                struct cmsghdr *cm = msg->msg_control;

                cm->cmsg_level = level;
                cm->cmsg_type = type;
                cm->cmsg_len = cmlen;
                memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
        }

        cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
        if (msg->msg_control_is_user)
                msg->msg_control_user += cmlen;
        else
                msg->msg_control += cmlen;
        msg->msg_controllen -= cmlen;
        return 0;

efault:
        return -EFAULT;
}
EXPORT_SYMBOL(put_cmsg);

int put_cmsg_notrunc(struct msghdr *msg, int level, int type, int len,
                     void *data)
{
        /* Don't produce truncated CMSGs */
        if (!msg->msg_control || msg->msg_controllen < CMSG_LEN(len))
                return -ETOOSMALL;

        return put_cmsg(msg, level, type, len, data);
}

void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
{
        struct scm_timestamping64 tss;
        int i;

        for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
                tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
                tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
        }

        put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
}
EXPORT_SYMBOL(put_cmsg_scm_timestamping64);

void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
{
        struct scm_timestamping tss;
        int i;

        for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
                tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
                tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
        }

        put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
}
EXPORT_SYMBOL(put_cmsg_scm_timestamping);

static int scm_max_fds(struct msghdr *msg)
{
        if (msg->msg_controllen <= sizeof(struct cmsghdr))
                return 0;
        return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
}

void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
{
        struct cmsghdr __user *cm =
                (__force struct cmsghdr __user *)msg->msg_control_user;
        unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
        int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
        int __user *cmsg_data = CMSG_USER_DATA(cm);
        int err = 0, i;

        /* no use for FD passing from kernel space callers */
        if (WARN_ON_ONCE(!msg->msg_control_is_user))
                return;

        if (msg->msg_flags & MSG_CMSG_COMPAT) {
                scm_detach_fds_compat(msg, scm);
                return;
        }

        for (i = 0; i < fdmax; i++) {
                err = scm_recv_one_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
                if (err < 0)
                        break;
        }

        if (i > 0) {
                int cmlen = CMSG_LEN(i * sizeof(int));

                err = put_user(SOL_SOCKET, &cm->cmsg_level);
                if (!err)
                        err = put_user(SCM_RIGHTS, &cm->cmsg_type);
                if (!err)
                        err = put_user(cmlen, &cm->cmsg_len);
                if (!err) {
                        cmlen = CMSG_SPACE(i * sizeof(int));
                        if (msg->msg_controllen < cmlen)
                                cmlen = msg->msg_controllen;
                        msg->msg_control_user += cmlen;
                        msg->msg_controllen -= cmlen;
                }
        }

        if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
                msg->msg_flags |= MSG_CTRUNC;

        /*
         * All of the files that fit in the message have had their usage counts
         * incremented, so we just free the list.
         */
        __scm_destroy(scm);
}
EXPORT_SYMBOL(scm_detach_fds);

struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
{
        struct scm_fp_list *new_fpl;
        int i;

        if (!fpl)
                return NULL;

        new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
                          GFP_KERNEL_ACCOUNT);
        if (new_fpl) {
                for (i = 0; i < fpl->count; i++)
                        get_file(fpl->fp[i]);

                new_fpl->max = new_fpl->count;
                new_fpl->user = get_uid(fpl->user);
#if IS_ENABLED(CONFIG_UNIX)
                new_fpl->inflight = false;
                new_fpl->edges = NULL;
                INIT_LIST_HEAD(&new_fpl->vertices);
#endif
        }
        return new_fpl;
}
EXPORT_SYMBOL(scm_fp_dup);

#ifdef CONFIG_SECURITY_NETWORK
static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
{
        struct lsm_context ctx;
        int err;

        if (sk->sk_scm_security) {
                err = security_secid_to_secctx(scm->secid, &ctx);

                if (err >= 0) {
                        put_cmsg(msg, SOL_SOCKET, SCM_SECURITY, ctx.len,
                                 ctx.context);

                        security_release_secctx(&ctx);
                }
        }
}

static bool scm_has_secdata(struct sock *sk)
{
        return sk->sk_scm_security;
}
#else
static void scm_passec(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm)
{
}

static bool scm_has_secdata(struct sock *sk)
{
        return false;
}
#endif

static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
{
        struct file *pidfd_file = NULL;
        int len, 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_flags & MSG_CMSG_COMPAT)
                len = sizeof(struct compat_cmsghdr) + sizeof(int);
        else
                len = sizeof(struct cmsghdr) + sizeof(int);

        if (msg->msg_controllen < len) {
                msg->msg_flags |= MSG_CTRUNC;
                return;
        }

        if (!scm->pid)
                return;

        pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &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 bool __scm_recv_common(struct sock *sk, struct msghdr *msg,
                              struct scm_cookie *scm, int flags)
{
        if (!msg->msg_control) {
                if (sk->sk_scm_credentials || sk->sk_scm_pidfd ||
                    scm->fp || scm_has_secdata(sk))
                        msg->msg_flags |= MSG_CTRUNC;

                scm_destroy(scm);
                return false;
        }

        if (sk->sk_scm_credentials) {
                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(sk, msg, scm);

        if (scm->fp)
                scm_detach_fds(msg, scm);

        return true;
}

void scm_recv(struct socket *sock, struct msghdr *msg,
              struct scm_cookie *scm, int flags)
{
        if (!__scm_recv_common(sock->sk, msg, scm, flags))
                return;

        scm_destroy_cred(scm);
}
EXPORT_SYMBOL(scm_recv);

void scm_recv_unix(struct socket *sock, struct msghdr *msg,
                   struct scm_cookie *scm, int flags)
{
        if (!__scm_recv_common(sock->sk, msg, scm, flags))
                return;

        if (sock->sk->sk_scm_pidfd)
                scm_pidfd_recv(msg, scm);

        scm_destroy_cred(scm);
}