/*
 * linux/ipc/msg.c
 * Copyright (C) 1992 Krishna Balasubramanian
 *
 * Removed all the remaining kerneld mess
 * Catch the -EFAULT stuff properly
 * Use GFP_KERNEL for messages as in 1.2
 * Fixed up the unchecked user space derefs
 * Copyright (C) 1998 Alan Cox & Andi Kleen
 *
 * /proc/sysvipc/msg support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
 *
 * mostly rewritten, threaded and wake-one semantics added
 * MSGMAX limit removed, sysctl's added
 * (c) 1999 Manfred Spraul <manfred@colorfullife.com>
 *
 * support for audit of ipc object properties and permission changes
 * Dustin Kirkland <dustin.kirkland@us.ibm.com>
 *
 * namespaces support
 * OpenVZ, SWsoft Inc.
 * Pavel Emelianov <xemul@openvz.org>
 */

#include <linux/capability.h>
#include <linux/msg.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/proc_fs.h>
#include <linux/list.h>
#include <linux/security.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>

#include <asm/current.h>
#include <linux/uaccess.h>
#include "util.h"

/* one msg_receiver structure for each sleeping receiver */
struct msg_receiver {
        struct list_head        r_list;
        struct task_struct      *r_tsk;

        int                     r_mode;
        long                    r_msgtype;
        long                    r_maxsize;

        struct msg_msg          *r_msg;
};

/* one msg_sender for each sleeping sender */
struct msg_sender {
        struct list_head        list;
        struct task_struct      *tsk;
        size_t                  msgsz;
};

#define SEARCH_ANY              1
#define SEARCH_EQUAL            2
#define SEARCH_NOTEQUAL         3
#define SEARCH_LESSEQUAL        4
#define SEARCH_NUMBER           5

#define msg_ids(ns)     ((ns)->ids[IPC_MSG_IDS])

static inline struct msg_queue *msq_obtain_object(struct ipc_namespace *ns, int id)
{
        struct kern_ipc_perm *ipcp = ipc_obtain_object_idr(&msg_ids(ns), id);

        if (IS_ERR(ipcp))
                return ERR_CAST(ipcp);

        return container_of(ipcp, struct msg_queue, q_perm);
}

static inline struct msg_queue *msq_obtain_object_check(struct ipc_namespace *ns,
                                                        int id)
{
        struct kern_ipc_perm *ipcp = ipc_obtain_object_check(&msg_ids(ns), id);

        if (IS_ERR(ipcp))
                return ERR_CAST(ipcp);

        return container_of(ipcp, struct msg_queue, q_perm);
}

static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s)
{
        ipc_rmid(&msg_ids(ns), &s->q_perm);
}

static void msg_rcu_free(struct rcu_head *head)
{
        struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu);
        struct msg_queue *msq = ipc_rcu_to_struct(p);

        security_msg_queue_free(msq);
        ipc_rcu_free(head);
}

/**
 * newque - Create a new msg queue
 * @ns: namespace
 * @params: ptr to the structure that contains the key and msgflg
 *
 * Called with msg_ids.rwsem held (writer)
 */
static int newque(struct ipc_namespace *ns, struct ipc_params *params)
{
        struct msg_queue *msq;
        int id, retval;
        key_t key = params->key;
        int msgflg = params->flg;

        msq = ipc_rcu_alloc(sizeof(*msq));
        if (!msq)
                return -ENOMEM;

        msq->q_perm.mode = msgflg & S_IRWXUGO;
        msq->q_perm.key = key;

        msq->q_perm.security = NULL;
        retval = security_msg_queue_alloc(msq);
        if (retval) {
                ipc_rcu_putref(msq, ipc_rcu_free);
                return retval;
        }

        msq->q_stime = msq->q_rtime = 0;
        msq->q_ctime = get_seconds();
        msq->q_cbytes = msq->q_qnum = 0;
        msq->q_qbytes = ns->msg_ctlmnb;
        msq->q_lspid = msq->q_lrpid = 0;
        INIT_LIST_HEAD(&msq->q_messages);
        INIT_LIST_HEAD(&msq->q_receivers);
        INIT_LIST_HEAD(&msq->q_senders);

        /* ipc_addid() locks msq upon success. */
        id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
        if (id < 0) {
                ipc_rcu_putref(msq, msg_rcu_free);
                return id;
        }

        ipc_unlock_object(&msq->q_perm);
        rcu_read_unlock();

        return msq->q_perm.id;
}

static inline bool msg_fits_inqueue(struct msg_queue *msq, size_t msgsz)
{
        return msgsz + msq->q_cbytes <= msq->q_qbytes &&
                1 + msq->q_qnum <= msq->q_qbytes;
}

static inline void ss_add(struct msg_queue *msq,
                          struct msg_sender *mss, size_t msgsz)
{
        mss->tsk = current;
        mss->msgsz = msgsz;
        __set_current_state(TASK_INTERRUPTIBLE);
        list_add_tail(&mss->list, &msq->q_senders);
}

static inline void ss_del(struct msg_sender *mss)
{
        if (mss->list.next)
                list_del(&mss->list);
}

static void ss_wakeup(struct msg_queue *msq,
                      struct wake_q_head *wake_q, bool kill)
{
        struct msg_sender *mss, *t;
        struct task_struct *stop_tsk = NULL;
        struct list_head *h = &msq->q_senders;

        list_for_each_entry_safe(mss, t, h, list) {
                if (kill)
                        mss->list.next = NULL;

                /*
                 * Stop at the first task we don't wakeup,
                 * we've already iterated the original
                 * sender queue.
                 */
                else if (stop_tsk == mss->tsk)
                        break;
                /*
                 * We are not in an EIDRM scenario here, therefore
                 * verify that we really need to wakeup the task.
                 * To maintain current semantics and wakeup order,
                 * move the sender to the tail on behalf of the
                 * blocked task.
                 */
                else if (!msg_fits_inqueue(msq, mss->msgsz)) {
                        if (!stop_tsk)
                                stop_tsk = mss->tsk;

                        list_move_tail(&mss->list, &msq->q_senders);
                        continue;
                }

                wake_q_add(wake_q, mss->tsk);
        }
}

static void expunge_all(struct msg_queue *msq, int res,
                        struct wake_q_head *wake_q)
{
        struct msg_receiver *msr, *t;

        list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
                wake_q_add(wake_q, msr->r_tsk);
                WRITE_ONCE(msr->r_msg, ERR_PTR(res));
        }
}

/*
 * freeque() wakes up waiters on the sender and receiver waiting queue,
 * removes the message queue from message queue ID IDR, and cleans up all the
 * messages associated with this queue.
 *
 * msg_ids.rwsem (writer) and the spinlock for this message queue are held
 * before freeque() is called. msg_ids.rwsem remains locked on exit.
 */
static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
        struct msg_msg *msg, *t;
        struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);
        DEFINE_WAKE_Q(wake_q);

        expunge_all(msq, -EIDRM, &wake_q);
        ss_wakeup(msq, &wake_q, true);
        msg_rmid(ns, msq);
        ipc_unlock_object(&msq->q_perm);
        wake_up_q(&wake_q);
        rcu_read_unlock();

        list_for_each_entry_safe(msg, t, &msq->q_messages, m_list) {
                atomic_dec(&ns->msg_hdrs);
                free_msg(msg);
        }
        atomic_sub(msq->q_cbytes, &ns->msg_bytes);
        ipc_rcu_putref(msq, msg_rcu_free);
}

/*
 * Called with msg_ids.rwsem and ipcp locked.
 */
static inline int msg_security(struct kern_ipc_perm *ipcp, int msgflg)
{
        struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm);

        return security_msg_queue_associate(msq, msgflg);
}

SYSCALL_DEFINE2(msgget, key_t, key, int, msgflg)
{
        struct ipc_namespace *ns;
        static const struct ipc_ops msg_ops = {
                .getnew = newque,
                .associate = msg_security,
        };
        struct ipc_params msg_params;

        ns = current->nsproxy->ipc_ns;

        msg_params.key = key;
        msg_params.flg = msgflg;

        return ipcget(ns, &msg_ids(ns), &msg_ops, &msg_params);
}

static inline unsigned long
copy_msqid_to_user(void __user *buf, struct msqid64_ds *in, int version)
{
        switch (version) {
        case IPC_64:
                return copy_to_user(buf, in, sizeof(*in));
        case IPC_OLD:
        {
                struct msqid_ds out;

                memset(&out, 0, sizeof(out));

                ipc64_perm_to_ipc_perm(&in->msg_perm, &out.msg_perm);

                out.msg_stime           = in->msg_stime;
                out.msg_rtime           = in->msg_rtime;
                out.msg_ctime           = in->msg_ctime;

                if (in->msg_cbytes > USHRT_MAX)
                        out.msg_cbytes  = USHRT_MAX;
                else
                        out.msg_cbytes  = in->msg_cbytes;
                out.msg_lcbytes         = in->msg_cbytes;

                if (in->msg_qnum > USHRT_MAX)
                        out.msg_qnum    = USHRT_MAX;
                else
                        out.msg_qnum    = in->msg_qnum;

                if (in->msg_qbytes > USHRT_MAX)
                        out.msg_qbytes  = USHRT_MAX;
                else
                        out.msg_qbytes  = in->msg_qbytes;
                out.msg_lqbytes         = in->msg_qbytes;

                out.msg_lspid           = in->msg_lspid;
                out.msg_lrpid           = in->msg_lrpid;

                return copy_to_user(buf, &out, sizeof(out));
        }
        default:
                return -EINVAL;
        }
}

static inline unsigned long
copy_msqid_from_user(struct msqid64_ds *out, void __user *buf, int version)
{
        switch (version) {
        case IPC_64:
                if (copy_from_user(out, buf, sizeof(*out)))
                        return -EFAULT;
                return 0;
        case IPC_OLD:
        {
                struct msqid_ds tbuf_old;

                if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
                        return -EFAULT;

                out->msg_perm.uid       = tbuf_old.msg_perm.uid;
                out->msg_perm.gid       = tbuf_old.msg_perm.gid;
                out->msg_perm.mode      = tbuf_old.msg_perm.mode;

                if (tbuf_old.msg_qbytes == 0)
                        out->msg_qbytes = tbuf_old.msg_lqbytes;
                else
                        out->msg_qbytes = tbuf_old.msg_qbytes;

                return 0;
        }
        default:
                return -EINVAL;
        }
}

/*
 * This function handles some msgctl commands which require the rwsem
 * to be held in write mode.
 * NOTE: no locks must be held, the rwsem is taken inside this function.
 */
static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
                       struct msqid_ds __user *buf, int version)
{
        struct kern_ipc_perm *ipcp;
        struct msqid64_ds uninitialized_var(msqid64);
        struct msg_queue *msq;
        int err;

        if (cmd == IPC_SET) {
                if (copy_msqid_from_user(&msqid64, buf, version))
                        return -EFAULT;
        }

        down_write(&msg_ids(ns).rwsem);
        rcu_read_lock();

        ipcp = ipcctl_pre_down_nolock(ns, &msg_ids(ns), msqid, cmd,
                                      &msqid64.msg_perm, msqid64.msg_qbytes);
        if (IS_ERR(ipcp)) {
                err = PTR_ERR(ipcp);
                goto out_unlock1;
        }

        msq = container_of(ipcp, struct msg_queue, q_perm);

        err = security_msg_queue_msgctl(msq, cmd);
        if (err)
                goto out_unlock1;

        switch (cmd) {
        case IPC_RMID:
                ipc_lock_object(&msq->q_perm);
                /* freeque unlocks the ipc object and rcu */
                freeque(ns, ipcp);
                goto out_up;
        case IPC_SET:
        {
                DEFINE_WAKE_Q(wake_q);

                if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
                    !capable(CAP_SYS_RESOURCE)) {
                        err = -EPERM;
                        goto out_unlock1;
                }

                ipc_lock_object(&msq->q_perm);
                err = ipc_update_perm(&msqid64.msg_perm, ipcp);
                if (err)
                        goto out_unlock0;

                msq->q_qbytes = msqid64.msg_qbytes;

                msq->q_ctime = get_seconds();
                /*
                 * Sleeping receivers might be excluded by
                 * stricter permissions.
                 */
                expunge_all(msq, -EAGAIN, &wake_q);
                /*
                 * Sleeping senders might be able to send
                 * due to a larger queue size.
                 */
                ss_wakeup(msq, &wake_q, false);
                ipc_unlock_object(&msq->q_perm);
                wake_up_q(&wake_q);

                goto out_unlock1;
        }
        default:
                err = -EINVAL;
                goto out_unlock1;
        }

out_unlock0:
        ipc_unlock_object(&msq->q_perm);
out_unlock1:
        rcu_read_unlock();
out_up:
        up_write(&msg_ids(ns).rwsem);
        return err;
}

static int msgctl_nolock(struct ipc_namespace *ns, int msqid,
                         int cmd, int version, void __user *buf)
{
        int err;
        struct msg_queue *msq;

        switch (cmd) {
        case IPC_INFO:
        case MSG_INFO:
        {
                struct msginfo msginfo;
                int max_id;

                if (!buf)
                        return -EFAULT;

                /*
                 * We must not return kernel stack data.
                 * due to padding, it's not enough
                 * to set all member fields.
                 */
                err = security_msg_queue_msgctl(NULL, cmd);
                if (err)
                        return err;

                memset(&msginfo, 0, sizeof(msginfo));
                msginfo.msgmni = ns->msg_ctlmni;
                msginfo.msgmax = ns->msg_ctlmax;
                msginfo.msgmnb = ns->msg_ctlmnb;
                msginfo.msgssz = MSGSSZ;
                msginfo.msgseg = MSGSEG;
                down_read(&msg_ids(ns).rwsem);
                if (cmd == MSG_INFO) {
                        msginfo.msgpool = msg_ids(ns).in_use;
                        msginfo.msgmap = atomic_read(&ns->msg_hdrs);
                        msginfo.msgtql = atomic_read(&ns->msg_bytes);
                } else {
                        msginfo.msgmap = MSGMAP;
                        msginfo.msgpool = MSGPOOL;
                        msginfo.msgtql = MSGTQL;
                }
                max_id = ipc_get_maxid(&msg_ids(ns));
                up_read(&msg_ids(ns).rwsem);
                if (copy_to_user(buf, &msginfo, sizeof(struct msginfo)))
                        return -EFAULT;
                return (max_id < 0) ? 0 : max_id;
        }

        case MSG_STAT:
        case IPC_STAT:
        {
                struct msqid64_ds tbuf;
                int success_return;

                if (!buf)
                        return -EFAULT;

                memset(&tbuf, 0, sizeof(tbuf));

                rcu_read_lock();
                if (cmd == MSG_STAT) {
                        msq = msq_obtain_object(ns, msqid);
                        if (IS_ERR(msq)) {
                                err = PTR_ERR(msq);
                                goto out_unlock;
                        }
                        success_return = msq->q_perm.id;
                } else {
                        msq = msq_obtain_object_check(ns, msqid);
                        if (IS_ERR(msq)) {
                                err = PTR_ERR(msq);
                                goto out_unlock;
                        }
                        success_return = 0;
                }

                err = -EACCES;
                if (ipcperms(ns, &msq->q_perm, S_IRUGO))
                        goto out_unlock;

                err = security_msg_queue_msgctl(msq, cmd);
                if (err)
                        goto out_unlock;

                kernel_to_ipc64_perm(&msq->q_perm, &tbuf.msg_perm);
                tbuf.msg_stime  = msq->q_stime;
                tbuf.msg_rtime  = msq->q_rtime;
                tbuf.msg_ctime  = msq->q_ctime;
                tbuf.msg_cbytes = msq->q_cbytes;
                tbuf.msg_qnum   = msq->q_qnum;
                tbuf.msg_qbytes = msq->q_qbytes;
                tbuf.msg_lspid  = msq->q_lspid;
                tbuf.msg_lrpid  = msq->q_lrpid;
                rcu_read_unlock();

                if (copy_msqid_to_user(buf, &tbuf, version))
                        return -EFAULT;
                return success_return;
        }

        default:
                return -EINVAL;
        }

        return err;
out_unlock:
        rcu_read_unlock();
        return err;
}

SYSCALL_DEFINE3(msgctl, int, msqid, int, cmd, struct msqid_ds __user *, buf)
{
        int version;
        struct ipc_namespace *ns;

        if (msqid < 0 || cmd < 0)
                return -EINVAL;

        version = ipc_parse_version(&cmd);
        ns = current->nsproxy->ipc_ns;

        switch (cmd) {
        case IPC_INFO:
        case MSG_INFO:
        case MSG_STAT:  /* msqid is an index rather than a msg queue id */
        case IPC_STAT:
                return msgctl_nolock(ns, msqid, cmd, version, buf);
        case IPC_SET:
        case IPC_RMID:
                return msgctl_down(ns, msqid, cmd, buf, version);
        default:
                return  -EINVAL;
        }
}

static int testmsg(struct msg_msg *msg, long type, int mode)
{
        switch (mode) {
        case SEARCH_ANY:
        case SEARCH_NUMBER:
                return 1;
        case SEARCH_LESSEQUAL:
                if (msg->m_type <= type)
                        return 1;
                break;
        case SEARCH_EQUAL:
                if (msg->m_type == type)
                        return 1;
                break;
        case SEARCH_NOTEQUAL:
                if (msg->m_type != type)
                        return 1;
                break;
        }
        return 0;
}

static inline int pipelined_send(struct msg_queue *msq, struct msg_msg *msg,
                                 struct wake_q_head *wake_q)
{
        struct msg_receiver *msr, *t;

        list_for_each_entry_safe(msr, t, &msq->q_receivers, r_list) {
                if (testmsg(msg, msr->r_msgtype, msr->r_mode) &&
                    !security_msg_queue_msgrcv(msq, msg, msr->r_tsk,
                                               msr->r_msgtype, msr->r_mode)) {

                        list_del(&msr->r_list);
                        if (msr->r_maxsize < msg->m_ts) {
                                wake_q_add(wake_q, msr->r_tsk);
                                WRITE_ONCE(msr->r_msg, ERR_PTR(-E2BIG));
                        } else {
                                msq->q_lrpid = task_pid_vnr(msr->r_tsk);
                                msq->q_rtime = get_seconds();

                                wake_q_add(wake_q, msr->r_tsk);
                                WRITE_ONCE(msr->r_msg, msg);
                                return 1;
                        }
                }
        }

        return 0;
}

long do_msgsnd(int msqid, long mtype, void __user *mtext,
                size_t msgsz, int msgflg)
{
        struct msg_queue *msq;
        struct msg_msg *msg;
        int err;
        struct ipc_namespace *ns;
        DEFINE_WAKE_Q(wake_q);

        ns = current->nsproxy->ipc_ns;

        if (msgsz > ns->msg_ctlmax || (long) msgsz < 0 || msqid < 0)
                return -EINVAL;
        if (mtype < 1)
                return -EINVAL;

        msg = load_msg(mtext, msgsz);
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        msg->m_type = mtype;
        msg->m_ts = msgsz;

        rcu_read_lock();
        msq = msq_obtain_object_check(ns, msqid);
        if (IS_ERR(msq)) {
                err = PTR_ERR(msq);
                goto out_unlock1;
        }

        ipc_lock_object(&msq->q_perm);

        for (;;) {
                struct msg_sender s;

                err = -EACCES;
                if (ipcperms(ns, &msq->q_perm, S_IWUGO))
                        goto out_unlock0;

                /* raced with RMID? */
                if (!ipc_valid_object(&msq->q_perm)) {
                        err = -EIDRM;
                        goto out_unlock0;
                }

                err = security_msg_queue_msgsnd(msq, msg, msgflg);
                if (err)
                        goto out_unlock0;

                if (msg_fits_inqueue(msq, msgsz))
                        break;

                /* queue full, wait: */
                if (msgflg & IPC_NOWAIT) {
                        err = -EAGAIN;
                        goto out_unlock0;
                }

                /* enqueue the sender and prepare to block */
                ss_add(msq, &s, msgsz);

                if (!ipc_rcu_getref(msq)) {
                        err = -EIDRM;
                        goto out_unlock0;
                }

                ipc_unlock_object(&msq->q_perm);
                rcu_read_unlock();
                schedule();

                rcu_read_lock();
                ipc_lock_object(&msq->q_perm);

                ipc_rcu_putref(msq, msg_rcu_free);
                /* raced with RMID? */
                if (!ipc_valid_object(&msq->q_perm)) {
                        err = -EIDRM;
                        goto out_unlock0;
                }
                ss_del(&s);

                if (signal_pending(current)) {
                        err = -ERESTARTNOHAND;
                        goto out_unlock0;
                }

        }

        msq->q_lspid = task_tgid_vnr(current);
        msq->q_stime = get_seconds();

        if (!pipelined_send(msq, msg, &wake_q)) {
                /* no one is waiting for this message, enqueue it */
                list_add_tail(&msg->m_list, &msq->q_messages);
                msq->q_cbytes += msgsz;
                msq->q_qnum++;
                atomic_add(msgsz, &ns->msg_bytes);
                atomic_inc(&ns->msg_hdrs);
        }

        err = 0;
        msg = NULL;

out_unlock0:
        ipc_unlock_object(&msq->q_perm);
        wake_up_q(&wake_q);
out_unlock1:
        rcu_read_unlock();
        if (msg != NULL)
                free_msg(msg);
        return err;
}

SYSCALL_DEFINE4(msgsnd, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
                int, msgflg)
{
        long mtype;

        if (get_user(mtype, &msgp->mtype))
                return -EFAULT;
        return do_msgsnd(msqid, mtype, msgp->mtext, msgsz, msgflg);
}

static inline int convert_mode(long *msgtyp, int msgflg)
{
        if (msgflg & MSG_COPY)
                return SEARCH_NUMBER;
        /*
         *  find message of correct type.
         *  msgtyp = 0 => get first.
         *  msgtyp > 0 => get first message of matching type.
         *  msgtyp < 0 => get message with least type must be < abs(msgtype).
         */
        if (*msgtyp == 0)
                return SEARCH_ANY;
        if (*msgtyp < 0) {
                if (*msgtyp == LONG_MIN) /* -LONG_MIN is undefined */
                        *msgtyp = LONG_MAX;
                else
                        *msgtyp = -*msgtyp;
                return SEARCH_LESSEQUAL;
        }
        if (msgflg & MSG_EXCEPT)
                return SEARCH_NOTEQUAL;
        return SEARCH_EQUAL;
}

static long do_msg_fill(void __user *dest, struct msg_msg *msg, size_t bufsz)
{
        struct msgbuf __user *msgp = dest;
        size_t msgsz;

        if (put_user(msg->m_type, &msgp->mtype))
                return -EFAULT;

        msgsz = (bufsz > msg->m_ts) ? msg->m_ts : bufsz;
        if (store_msg(msgp->mtext, msg, msgsz))
                return -EFAULT;
        return msgsz;
}

#ifdef CONFIG_CHECKPOINT_RESTORE
/*
 * This function creates new kernel message structure, large enough to store
 * bufsz message bytes.
 */
static inline struct msg_msg *prepare_copy(void __user *buf, size_t bufsz)
{
        struct msg_msg *copy;

        /*
         * Create dummy message to copy real message to.
         */
        copy = load_msg(buf, bufsz);
        if (!IS_ERR(copy))
                copy->m_ts = bufsz;
        return copy;
}

static inline void free_copy(struct msg_msg *copy)
{
        if (copy)
                free_msg(copy);
}
#else
static inline struct msg_msg *prepare_copy(void __user *buf, size_t bufsz)
{
        return ERR_PTR(-ENOSYS);
}

static inline void free_copy(struct msg_msg *copy)
{
}
#endif

static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode)
{
        struct msg_msg *msg, *found = NULL;
        long count = 0;

        list_for_each_entry(msg, &msq->q_messages, m_list) {
                if (testmsg(msg, *msgtyp, mode) &&
                    !security_msg_queue_msgrcv(msq, msg, current,
                                               *msgtyp, mode)) {
                        if (mode == SEARCH_LESSEQUAL && msg->m_type != 1) {
                                *msgtyp = msg->m_type - 1;
                                found = msg;
                        } else if (mode == SEARCH_NUMBER) {
                                if (*msgtyp == count)
                                        return msg;
                        } else
                                return msg;
                        count++;
                }
        }

        return found ?: ERR_PTR(-EAGAIN);
}

long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgflg,
               long (*msg_handler)(void __user *, struct msg_msg *, size_t))
{
        int mode;
        struct msg_queue *msq;
        struct ipc_namespace *ns;
        struct msg_msg *msg, *copy = NULL;
        DEFINE_WAKE_Q(wake_q);

        ns = current->nsproxy->ipc_ns;

        if (msqid < 0 || (long) bufsz < 0)
                return -EINVAL;

        if (msgflg & MSG_COPY) {
                if ((msgflg & MSG_EXCEPT) || !(msgflg & IPC_NOWAIT))
                        return -EINVAL;
                copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax));
                if (IS_ERR(copy))
                        return PTR_ERR(copy);
        }
        mode = convert_mode(&msgtyp, msgflg);

        rcu_read_lock();
        msq = msq_obtain_object_check(ns, msqid);
        if (IS_ERR(msq)) {
                rcu_read_unlock();
                free_copy(copy);
                return PTR_ERR(msq);
        }

        for (;;) {
                struct msg_receiver msr_d;

                msg = ERR_PTR(-EACCES);
                if (ipcperms(ns, &msq->q_perm, S_IRUGO))
                        goto out_unlock1;

                ipc_lock_object(&msq->q_perm);

                /* raced with RMID? */
                if (!ipc_valid_object(&msq->q_perm)) {
                        msg = ERR_PTR(-EIDRM);
                        goto out_unlock0;
                }

                msg = find_msg(msq, &msgtyp, mode);
                if (!IS_ERR(msg)) {
                        /*
                         * Found a suitable message.
                         * Unlink it from the queue.
                         */
                        if ((bufsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
                                msg = ERR_PTR(-E2BIG);
                                goto out_unlock0;
                        }
                        /*
                         * If we are copying, then do not unlink message and do
                         * not update queue parameters.
                         */
                        if (msgflg & MSG_COPY) {
                                msg = copy_msg(msg, copy);
                                goto out_unlock0;
                        }

                        list_del(&msg->m_list);
                        msq->q_qnum--;
                        msq->q_rtime = get_seconds();
                        msq->q_lrpid = task_tgid_vnr(current);
                        msq->q_cbytes -= msg->m_ts;
                        atomic_sub(msg->m_ts, &ns->msg_bytes);
                        atomic_dec(&ns->msg_hdrs);
                        ss_wakeup(msq, &wake_q, false);

                        goto out_unlock0;
                }

                /* No message waiting. Wait for a message */
                if (msgflg & IPC_NOWAIT) {
                        msg = ERR_PTR(-ENOMSG);
                        goto out_unlock0;
                }

                list_add_tail(&msr_d.r_list, &msq->q_receivers);
                msr_d.r_tsk = current;
                msr_d.r_msgtype = msgtyp;
                msr_d.r_mode = mode;
                if (msgflg & MSG_NOERROR)
                        msr_d.r_maxsize = INT_MAX;
                else
                        msr_d.r_maxsize = bufsz;
                msr_d.r_msg = ERR_PTR(-EAGAIN);
                __set_current_state(TASK_INTERRUPTIBLE);

                ipc_unlock_object(&msq->q_perm);
                rcu_read_unlock();
                schedule();

                /*
                 * Lockless receive, part 1:
                 * We don't hold a reference to the queue and getting a
                 * reference would defeat the idea of a lockless operation,
                 * thus the code relies on rcu to guarantee the existence of
                 * msq:
                 * Prior to destruction, expunge_all(-EIRDM) changes r_msg.
                 * Thus if r_msg is -EAGAIN, then the queue not yet destroyed.
                 */
                rcu_read_lock();

                /*
                 * Lockless receive, part 2:
                 * The work in pipelined_send() and expunge_all():
                 * - Set pointer to message
                 * - Queue the receiver task for later wakeup
                 * - Wake up the process after the lock is dropped.
                 *
                 * Should the process wake up before this wakeup (due to a
                 * signal) it will either see the message and continue ...
                 */
                msg = READ_ONCE(msr_d.r_msg);
                if (msg != ERR_PTR(-EAGAIN))
                        goto out_unlock1;

                 /*
                  * ... or see -EAGAIN, acquire the lock to check the message
                  * again.
                  */
                ipc_lock_object(&msq->q_perm);

                msg = msr_d.r_msg;
                if (msg != ERR_PTR(-EAGAIN))
                        goto out_unlock0;

                list_del(&msr_d.r_list);
                if (signal_pending(current)) {
                        msg = ERR_PTR(-ERESTARTNOHAND);
                        goto out_unlock0;
                }

                ipc_unlock_object(&msq->q_perm);
        }

out_unlock0:
        ipc_unlock_object(&msq->q_perm);
        wake_up_q(&wake_q);
out_unlock1:
        rcu_read_unlock();
        if (IS_ERR(msg)) {
                free_copy(copy);
                return PTR_ERR(msg);
        }

        bufsz = msg_handler(buf, msg, bufsz);
        free_msg(msg);

        return bufsz;
}

SYSCALL_DEFINE5(msgrcv, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
                long, msgtyp, int, msgflg)
{
        return do_msgrcv(msqid, msgp, msgsz, msgtyp, msgflg, do_msg_fill);
}


void msg_init_ns(struct ipc_namespace *ns)
{
        ns->msg_ctlmax = MSGMAX;
        ns->msg_ctlmnb = MSGMNB;
        ns->msg_ctlmni = MSGMNI;

        atomic_set(&ns->msg_bytes, 0);
        atomic_set(&ns->msg_hdrs, 0);
        ipc_init_ids(&ns->ids[IPC_MSG_IDS]);
}

#ifdef CONFIG_IPC_NS
void msg_exit_ns(struct ipc_namespace *ns)
{
        free_ipcs(ns, &msg_ids(ns), freeque);
        idr_destroy(&ns->ids[IPC_MSG_IDS].ipcs_idr);
}
#endif

#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
{
        struct user_namespace *user_ns = seq_user_ns(s);
        struct msg_queue *msq = it;

        seq_printf(s,
                   "%10d %10d  %4o  %10lu %10lu %5u %5u %5u %5u %5u %5u %10lu %10lu %10lu\n",
                   msq->q_perm.key,
                   msq->q_perm.id,
                   msq->q_perm.mode,
                   msq->q_cbytes,
                   msq->q_qnum,
                   msq->q_lspid,
                   msq->q_lrpid,
                   from_kuid_munged(user_ns, msq->q_perm.uid),
                   from_kgid_munged(user_ns, msq->q_perm.gid),
                   from_kuid_munged(user_ns, msq->q_perm.cuid),
                   from_kgid_munged(user_ns, msq->q_perm.cgid),
                   msq->q_stime,
                   msq->q_rtime,
                   msq->q_ctime);

        return 0;
}
#endif

void __init msg_init(void)
{
        msg_init_ns(&init_ipc_ns);

        ipc_init_proc_interface("sysvipc/msg",
                                "       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
                                IPC_MSG_IDS, sysvipc_msg_proc_show);
}