/* * 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 * * mostly rewritten, threaded and wake-one semantics added * MSGMAX limit removed, sysctl's added * (c) 1999 Manfred Spraul * * support for audit of ipc object properties and permission changes * Dustin Kirkland * * namespaces support * OpenVZ, SWsoft Inc. * Pavel Emelianov */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #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 *volatile r_msg; }; /* one msg_sender for each sleeping sender */ struct msg_sender { struct list_head list; struct task_struct *tsk; }; #define SEARCH_ANY 1 #define SEARCH_EQUAL 2 #define SEARCH_NOTEQUAL 3 #define SEARCH_LESSEQUAL 4 #define msg_ids(ns) ((ns)->ids[IPC_MSG_IDS]) #define msg_unlock(msq) ipc_unlock(&(msq)->q_perm) static void freeque(struct ipc_namespace *, struct kern_ipc_perm *); static int newque(struct ipc_namespace *, struct ipc_params *); #ifdef CONFIG_PROC_FS static int sysvipc_msg_proc_show(struct seq_file *s, void *it); #endif /* * Scale msgmni with the available lowmem size: the memory dedicated to msg * queues should occupy at most 1/MSG_MEM_SCALE of lowmem. * Also take into account the number of nsproxies created so far. * This should be done staying within the (MSGMNI , IPCMNI/nr_ipc_ns) range. */ void recompute_msgmni(struct ipc_namespace *ns) { struct sysinfo i; unsigned long allowed; int nb_ns; si_meminfo(&i); allowed = (((i.totalram - i.totalhigh) / MSG_MEM_SCALE) * i.mem_unit) / MSGMNB; nb_ns = atomic_read(&nr_ipc_ns); allowed /= nb_ns; if (allowed < MSGMNI) { ns->msg_ctlmni = MSGMNI; return; } if (allowed > IPCMNI / nb_ns) { ns->msg_ctlmni = IPCMNI / nb_ns; return; } ns->msg_ctlmni = allowed; } void msg_init_ns(struct ipc_namespace *ns) { ns->msg_ctlmax = MSGMAX; ns->msg_ctlmnb = MSGMNB; recompute_msgmni(ns); 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 void __init msg_init(void) { msg_init_ns(&init_ipc_ns); printk(KERN_INFO "msgmni has been set to %d\n", init_ipc_ns.msg_ctlmni); 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); } /* * msg_lock_(check_) routines are called in the paths where the rw_mutex * is not held. */ static inline struct msg_queue *msg_lock(struct ipc_namespace *ns, int id) { struct kern_ipc_perm *ipcp = ipc_lock(&msg_ids(ns), id); if (IS_ERR(ipcp)) return (struct msg_queue *)ipcp; return container_of(ipcp, struct msg_queue, q_perm); } static inline struct msg_queue *msg_lock_check(struct ipc_namespace *ns, int id) { struct kern_ipc_perm *ipcp = ipc_lock_check(&msg_ids(ns), id); if (IS_ERR(ipcp)) return (struct msg_queue *)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); } /** * newque - Create a new msg queue * @ns: namespace * @params: ptr to the structure that contains the key and msgflg * * Called with msg_ids.rw_mutex 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); return retval; } /* * ipc_addid() locks msq */ id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni); if (id < 0) { security_msg_queue_free(msq); ipc_rcu_putref(msq); return id; } 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); msg_unlock(msq); return msq->q_perm.id; } static inline void ss_add(struct msg_queue *msq, struct msg_sender *mss) { mss->tsk = current; 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 != NULL) list_del(&mss->list); } static void ss_wakeup(struct list_head *h, int kill) { struct list_head *tmp; tmp = h->next; while (tmp != h) { struct msg_sender *mss; mss = list_entry(tmp, struct msg_sender, list); tmp = tmp->next; if (kill) mss->list.next = NULL; wake_up_process(mss->tsk); } } static void expunge_all(struct msg_queue *msq, int res) { struct list_head *tmp; tmp = msq->q_receivers.next; while (tmp != &msq->q_receivers) { struct msg_receiver *msr; /* * Make sure that the wakeup doesnt preempt * this CPU prematurely. (on PREEMPT_RT) */ preempt_disable_rt(); msr = list_entry(tmp, struct msg_receiver, r_list); tmp = tmp->next; msr->r_msg = NULL; wake_up_process(msr->r_tsk); smp_mb(); msr->r_msg = ERR_PTR(res); preempt_enable_rt(); } } /* * 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.rw_mutex (writer) and the spinlock for this message queue are held * before freeque() is called. msg_ids.rw_mutex remains locked on exit. */ static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) { struct list_head *tmp; struct msg_queue *msq = container_of(ipcp, struct msg_queue, q_perm); expunge_all(msq, -EIDRM); ss_wakeup(&msq->q_senders, 1); msg_rmid(ns, msq); msg_unlock(msq); tmp = msq->q_messages.next; while (tmp != &msq->q_messages) { struct msg_msg *msg = list_entry(tmp, struct msg_msg, m_list); tmp = tmp->next; atomic_dec(&ns->msg_hdrs); free_msg(msg); } atomic_sub(msq->q_cbytes, &ns->msg_bytes); security_msg_queue_free(msq); ipc_rcu_putref(msq); } /* * Called with msg_ids.rw_mutex 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; struct ipc_ops msg_ops; struct ipc_params msg_params; ns = current->nsproxy->ipc_ns; msg_ops.getnew = newque; msg_ops.associate = msg_security; msg_ops.more_checks = NULL; 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 rw_mutex * to be held in write mode. * NOTE: no locks must be held, the rw_mutex 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; } ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd, &msqid64.msg_perm, msqid64.msg_qbytes); if (IS_ERR(ipcp)) return PTR_ERR(ipcp); msq = container_of(ipcp, struct msg_queue, q_perm); err = security_msg_queue_msgctl(msq, cmd); if (err) goto out_unlock; switch (cmd) { case IPC_RMID: freeque(ns, ipcp); goto out_up; case IPC_SET: if (msqid64.msg_qbytes > ns->msg_ctlmnb && !capable(CAP_SYS_RESOURCE)) { err = -EPERM; goto out_unlock; } err = ipc_update_perm(&msqid64.msg_perm, ipcp); if (err) goto out_unlock; msq->q_qbytes = msqid64.msg_qbytes; msq->q_ctime = get_seconds(); /* sleeping receivers might be excluded by * stricter permissions. */ expunge_all(msq, -EAGAIN); /* sleeping senders might be able to send * due to a larger queue size. */ ss_wakeup(&msq->q_senders, 0); break; default: err = -EINVAL; } out_unlock: msg_unlock(msq); out_up: up_write(&msg_ids(ns).rw_mutex); return err; } SYSCALL_DEFINE3(msgctl, int, msqid, int, cmd, struct msqid_ds __user *, buf) { struct msg_queue *msq; int err, 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: { 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).rw_mutex); 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).rw_mutex); if (copy_to_user(buf, &msginfo, sizeof(struct msginfo))) return -EFAULT; return (max_id < 0) ? 0 : max_id; } case MSG_STAT: /* msqid is an index rather than a msg queue id */ case IPC_STAT: { struct msqid64_ds tbuf; int success_return; if (!buf) return -EFAULT; if (cmd == MSG_STAT) { msq = msg_lock(ns, msqid); if (IS_ERR(msq)) return PTR_ERR(msq); success_return = msq->q_perm.id; } else { msq = msg_lock_check(ns, msqid); if (IS_ERR(msq)) return PTR_ERR(msq); 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; memset(&tbuf, 0, sizeof(tbuf)); 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; msg_unlock(msq); if (copy_msqid_to_user(buf, &tbuf, version)) return -EFAULT; return success_return; } case IPC_SET: case IPC_RMID: err = msgctl_down(ns, msqid, cmd, buf, version); return err; default: return -EINVAL; } out_unlock: msg_unlock(msq); return err; } static int testmsg(struct msg_msg *msg, long type, int mode) { switch(mode) { case SEARCH_ANY: 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 list_head *tmp; tmp = msq->q_receivers.next; while (tmp != &msq->q_receivers) { struct msg_receiver *msr; msr = list_entry(tmp, struct msg_receiver, r_list); tmp = tmp->next; if (testmsg(msg, msr->r_msgtype, msr->r_mode) && !security_msg_queue_msgrcv(msq, msg, msr->r_tsk, msr->r_msgtype, msr->r_mode)) { /* * Make sure that the wakeup doesnt preempt * this CPU prematurely. (on PREEMPT_RT) */ preempt_disable_rt(); list_del(&msr->r_list); if (msr->r_maxsize < msg->m_ts) { msr->r_msg = NULL; wake_up_process(msr->r_tsk); smp_mb(); msr->r_msg = ERR_PTR(-E2BIG); } else { msr->r_msg = NULL; msq->q_lrpid = task_pid_vnr(msr->r_tsk); msq->q_rtime = get_seconds(); wake_up_process(msr->r_tsk); smp_mb(); msr->r_msg = msg; preempt_enable_rt(); return 1; } preempt_enable_rt(); } } 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; 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; msq = msg_lock_check(ns, msqid); if (IS_ERR(msq)) { err = PTR_ERR(msq); goto out_free; } for (;;) { struct msg_sender s; err = -EACCES; if (ipcperms(ns, &msq->q_perm, S_IWUGO)) goto out_unlock_free; err = security_msg_queue_msgsnd(msq, msg, msgflg); if (err) goto out_unlock_free; if (msgsz + msq->q_cbytes <= msq->q_qbytes && 1 + msq->q_qnum <= msq->q_qbytes) { break; } /* queue full, wait: */ if (msgflg & IPC_NOWAIT) { err = -EAGAIN; goto out_unlock_free; } ss_add(msq, &s); ipc_rcu_getref(msq); msg_unlock(msq); schedule(); ipc_lock_by_ptr(&msq->q_perm); ipc_rcu_putref(msq); if (msq->q_perm.deleted) { err = -EIDRM; goto out_unlock_free; } ss_del(&s); if (signal_pending(current)) { err = -ERESTARTNOHAND; goto out_unlock_free; } } msq->q_lspid = task_tgid_vnr(current); msq->q_stime = get_seconds(); if (!pipelined_send(msq, msg)) { /* 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_unlock_free: msg_unlock(msq); out_free: 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) { /* * 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) { *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, int msgflg, long *msgtyp, unsigned long *copy_number) { struct msg_msg *copy; *copy_number = *msgtyp; *msgtyp = 0; /* * 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, int msgflg, long *msgtyp, unsigned long *copy_number) { return ERR_PTR(-ENOSYS); } static inline void free_copy(struct msg_msg *copy) { } #endif 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)) { struct msg_queue *msq; struct msg_msg *msg; int mode; struct ipc_namespace *ns; struct msg_msg *copy = NULL; unsigned long copy_number = 0; ns = current->nsproxy->ipc_ns; if (msqid < 0 || (long) bufsz < 0) return -EINVAL; if (msgflg & MSG_COPY) { copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax), msgflg, &msgtyp, ©_number); if (IS_ERR(copy)) return PTR_ERR(copy); } mode = convert_mode(&msgtyp, msgflg); msq = msg_lock_check(ns, msqid); if (IS_ERR(msq)) { free_copy(copy); return PTR_ERR(msq); } for (;;) { struct msg_receiver msr_d; struct list_head *tmp; long msg_counter = 0; msg = ERR_PTR(-EACCES); if (ipcperms(ns, &msq->q_perm, S_IRUGO)) goto out_unlock; msg = ERR_PTR(-EAGAIN); tmp = msq->q_messages.next; while (tmp != &msq->q_messages) { struct msg_msg *walk_msg; walk_msg = list_entry(tmp, struct msg_msg, m_list); if (testmsg(walk_msg, msgtyp, mode) && !security_msg_queue_msgrcv(msq, walk_msg, current, msgtyp, mode)) { msg = walk_msg; if (mode == SEARCH_LESSEQUAL && walk_msg->m_type != 1) { msgtyp = walk_msg->m_type - 1; } else if (msgflg & MSG_COPY) { if (copy_number == msg_counter) { /* * Found requested message. * Copy it. */ msg = copy_msg(msg, copy); if (IS_ERR(msg)) goto out_unlock; break; } msg = ERR_PTR(-EAGAIN); } else break; msg_counter++; } tmp = tmp->next; } 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_unlock; } /* * If we are copying, then do not unlink message and do * not update queue parameters. */ if (msgflg & MSG_COPY) goto out_unlock; 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->q_senders, 0); msg_unlock(msq); break; } /* No message waiting. Wait for a message */ if (msgflg & IPC_NOWAIT) { msg = ERR_PTR(-ENOMSG); goto out_unlock; } 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); current->state = TASK_INTERRUPTIBLE; msg_unlock(msq); schedule(); /* Lockless receive, part 1: * Disable preemption. 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() prevents preemption between reading r_msg * and the spin_lock() inside ipc_lock_by_ptr(). */ rcu_read_lock(); /* Lockless receive, part 2: * Wait until pipelined_send or expunge_all are outside of * wake_up_process(). There is a race with exit(), see * ipc/mqueue.c for the details. */ msg = (struct msg_msg*)msr_d.r_msg; while (msg == NULL) { cpu_relax(); msg = (struct msg_msg *)msr_d.r_msg; } /* Lockless receive, part 3: * If there is a message or an error then accept it without * locking. */ if (msg != ERR_PTR(-EAGAIN)) { rcu_read_unlock(); break; } /* Lockless receive, part 3: * Acquire the queue spinlock. */ ipc_lock_by_ptr(&msq->q_perm); rcu_read_unlock(); /* Lockless receive, part 4: * Repeat test after acquiring the spinlock. */ msg = (struct msg_msg*)msr_d.r_msg; if (msg != ERR_PTR(-EAGAIN)) goto out_unlock; list_del(&msr_d.r_list); if (signal_pending(current)) { msg = ERR_PTR(-ERESTARTNOHAND); out_unlock: msg_unlock(msq); break; } } 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); } #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; return 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); } #endif