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DEFINITIONS
This source file includes following definitions.
- recompute_msgmni
- msg_init_ns
- msg_exit_ns
- msg_init
- msg_lock
- msg_lock_check
- msg_rmid
- newque
- ss_add
- ss_del
- ss_wakeup
- expunge_all
- freeque
- msg_security
- sys_msgget
- copy_msqid_to_user
- copy_msqid_from_user
- msgctl_down
- sys_msgctl
- testmsg
- pipelined_send
- do_msgsnd
- sys_msgsnd
- convert_mode
- do_msgrcv
- sys_msgrcv
- sysvipc_msg_proc_show
/*
* 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/slab.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 <asm/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 *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);
}
#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;
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);
}
}
/*
* 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);
}
asmlinkage long sys_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 > USHORT_MAX)
out.msg_cbytes = USHORT_MAX;
else
out.msg_cbytes = in->msg_cbytes;
out.msg_lcbytes = in->msg_cbytes;
if (in->msg_qnum > USHORT_MAX)
out.msg_qnum = USHORT_MAX;
else
out.msg_qnum = in->msg_qnum;
if (in->msg_qbytes > USHORT_MAX)
out.msg_qbytes = USHORT_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 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(&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;
}
msq->q_qbytes = msqid64.msg_qbytes;
ipc_update_perm(&msqid64.msg_perm, ipcp);
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;
}
asmlinkage long sys_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(&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)) {
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;
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;
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(&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)) {
/* noone 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;
}
asmlinkage long
sys_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;
}
long do_msgrcv(int msqid, long *pmtype, void __user *mtext,
size_t msgsz, long msgtyp, int msgflg)
{
struct msg_queue *msq;
struct msg_msg *msg;
int mode;
struct ipc_namespace *ns;
if (msqid < 0 || (long) msgsz < 0)
return -EINVAL;
mode = convert_mode(&msgtyp, msgflg);
ns = current->nsproxy->ipc_ns;
msq = msg_lock_check(ns, msqid);
if (IS_ERR(msq))
return PTR_ERR(msq);
for (;;) {
struct msg_receiver msr_d;
struct list_head *tmp;
msg = ERR_PTR(-EACCES);
if (ipcperms(&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) {
msg = walk_msg;
msgtyp = walk_msg->m_type - 1;
} else {
msg = walk_msg;
break;
}
}
tmp = tmp->next;
}
if (!IS_ERR(msg)) {
/*
* Found a suitable message.
* Unlink it from the queue.
*/
if ((msgsz < msg->m_ts) && !(msgflg & MSG_NOERROR)) {
msg = ERR_PTR(-E2BIG);
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 = msgsz;
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
* existance 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))
return PTR_ERR(msg);
msgsz = (msgsz > msg->m_ts) ? msg->m_ts : msgsz;
*pmtype = msg->m_type;
if (store_msg(mtext, msg, msgsz))
msgsz = -EFAULT;
free_msg(msg);
return msgsz;
}
asmlinkage long sys_msgrcv(int msqid, struct msgbuf __user *msgp, size_t msgsz,
long msgtyp, int msgflg)
{
long err, mtype;
err = do_msgrcv(msqid, &mtype, msgp->mtext, msgsz, msgtyp, msgflg);
if (err < 0)
goto out;
if (put_user(mtype, &msgp->mtype))
err = -EFAULT;
out:
return err;
}
#ifdef CONFIG_PROC_FS
static int sysvipc_msg_proc_show(struct seq_file *s, void *it)
{
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,
msq->q_perm.uid,
msq->q_perm.gid,
msq->q_perm.cuid,
msq->q_perm.cgid,
msq->q_stime,
msq->q_rtime,
msq->q_ctime);
}
#endif