SysV can be abused to allocated locked kernel memory.
For most systems, a small limit doesn't make sense,
see the discussion with regards to SHMMAX.

Therefore: increase MSGMNI to the maximum supported.

And: if we ignore the risk of locking too much memory, then
an automatic scaling of MSGMNI doesn't make sense.

Therefore: remove the whole logic.

Note:
If an administrator must limit the memory allocations, then
he can set MSGMNI as necessary.

Or he can disable sysv entirely (as e.g. done with Android).
---
 include/linux/ipc_namespace.h | 20 ----------
 include/uapi/linux/msg.h      | 12 +-----
 ipc/Makefile                  |  2 +-
 ipc/ipc_sysctl.c              | 87 +---------------------------------------
 ipc/ipcns_notifier.c          | 92 -------------------------------------------
 ipc/msg.c                     | 36 +----------------
 ipc/namespace.c               | 22 -----------
 ipc/util.c                    | 40 -------------------
 8 files changed, 4 insertions(+), 307 deletions(-)
 delete mode 100644 ipc/ipcns_notifier.c

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 35e7eca..e365d5e 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -7,15 +7,6 @@
 #include <linux/notifier.h>
 #include <linux/nsproxy.h>
 
-/*
- * ipc namespace events
- */
-#define IPCNS_MEMCHANGED   0x00000001   /* Notify lowmem size changed */
-#define IPCNS_CREATED  0x00000002   /* Notify new ipc namespace created */
-#define IPCNS_REMOVED  0x00000003   /* Notify ipc namespace removed */
-
-#define IPCNS_CALLBACK_PRI 0
-
 struct user_namespace;
 
 struct ipc_ids {
@@ -38,7 +29,6 @@ struct ipc_namespace {
        unsigned int    msg_ctlmni;
        atomic_t        msg_bytes;
        atomic_t        msg_hdrs;
-       int             auto_msgmni;
 
        size_t          shm_ctlmax;
        size_t          shm_ctlall;
@@ -77,18 +67,8 @@ extern atomic_t nr_ipc_ns;
 extern spinlock_t mq_lock;
 
 #ifdef CONFIG_SYSVIPC
-extern int register_ipcns_notifier(struct ipc_namespace *);
-extern int cond_register_ipcns_notifier(struct ipc_namespace *);
-extern void unregister_ipcns_notifier(struct ipc_namespace *);
-extern int ipcns_notify(unsigned long);
 extern void shm_destroy_orphaned(struct ipc_namespace *ns);
 #else /* CONFIG_SYSVIPC */
-static inline int register_ipcns_notifier(struct ipc_namespace *ns)
-{ return 0; }
-static inline int cond_register_ipcns_notifier(struct ipc_namespace *ns)
-{ return 0; }
-static inline void unregister_ipcns_notifier(struct ipc_namespace *ns) { }
-static inline int ipcns_notify(unsigned long l) { return 0; }
 static inline void shm_destroy_orphaned(struct ipc_namespace *ns) {}
 #endif /* CONFIG_SYSVIPC */
 
diff --git a/include/uapi/linux/msg.h b/include/uapi/linux/msg.h
index a703755..ae9ddd2 100644
--- a/include/uapi/linux/msg.h
+++ b/include/uapi/linux/msg.h
@@ -50,17 +50,7 @@ struct msginfo {
        unsigned short  msgseg; 
 };
 
-/*
- * Scaling factor to compute msgmni:
- * the memory dedicated to msg queues (msgmni * msgmnb) should occupy
- * at most 1/MSG_MEM_SCALE of the lowmem (see the formula in ipc/msg.c):
- * up to 8MB       : msgmni = 16 (MSGMNI)
- * 4 GB            : msgmni = 8K
- * more than 16 GB : msgmni = 32K (IPCMNI)
- */
-#define MSG_MEM_SCALE 32
-
-#define MSGMNI    16   /* <= IPCMNI */     /* max # of msg queue identifiers */
+#define MSGMNI 32000   /* <= IPCMNI */     /* max # of msg queue identifiers */
 #define MSGMAX  8192   /* <= INT_MAX */   /* max size of message (bytes) */
 #define MSGMNB 16384   /* <= INT_MAX */   /* default max size of a message 
queue */
 
diff --git a/ipc/Makefile b/ipc/Makefile
index 9075e17..86c7300 100644
--- a/ipc/Makefile
+++ b/ipc/Makefile
@@ -3,7 +3,7 @@
 #
 
 obj-$(CONFIG_SYSVIPC_COMPAT) += compat.o
-obj-$(CONFIG_SYSVIPC) += util.o msgutil.o msg.o sem.o shm.o ipcns_notifier.o 
syscall.o
+obj-$(CONFIG_SYSVIPC) += util.o msgutil.o msg.o sem.o shm.o syscall.o
 obj-$(CONFIG_SYSVIPC_SYSCTL) += ipc_sysctl.o
 obj_mq-$(CONFIG_COMPAT) += compat_mq.o
 obj-$(CONFIG_POSIX_MQUEUE) += mqueue.o msgutil.o $(obj_mq-y)
diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
index 998d31b..cc34646 100644
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -62,29 +62,6 @@ static int proc_ipc_dointvec_minmax_orphans(ctl_table 
*table, int write,
        return err;
 }
 
-static int proc_ipc_callback_dointvec_minmax(ctl_table *table, int write,
-       void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-       struct ctl_table ipc_table;
-       size_t lenp_bef = *lenp;
-       int rc;
-
-       memcpy(&ipc_table, table, sizeof(ipc_table));
-       ipc_table.data = get_ipc(table);
-
-       rc = proc_dointvec_minmax(&ipc_table, write, buffer, lenp, ppos);
-
-       if (write && !rc && lenp_bef == *lenp)
-               /*
-                * Tunable has successfully been changed by hand. Disable its
-                * automatic adjustment. This simply requires unregistering
-                * the notifiers that trigger recalculation.
-                */
-               unregister_ipcns_notifier(current->nsproxy->ipc_ns);
-
-       return rc;
-}
-
 static int proc_ipc_doulongvec_minmax(ctl_table *table, int write,
        void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -96,64 +73,11 @@ static int proc_ipc_doulongvec_minmax(ctl_table *table, int 
write,
                                        lenp, ppos);
 }
 
-/*
- * Routine that is called when the file "auto_msgmni" has successfully been
- * written.
- * Two values are allowed:
- * 0: unregister msgmni's callback routine from the ipc namespace notifier
- *    chain. This means that msgmni won't be recomputed anymore upon memory
- *    add/remove or ipc namespace creation/removal.
- * 1: register back the callback routine.
- */
-static void ipc_auto_callback(int val)
-{
-       if (!val)
-               unregister_ipcns_notifier(current->nsproxy->ipc_ns);
-       else {
-               /*
-                * Re-enable automatic recomputing only if not already
-                * enabled.
-                */
-               recompute_msgmni(current->nsproxy->ipc_ns);
-               cond_register_ipcns_notifier(current->nsproxy->ipc_ns);
-       }
-}
-
-static int proc_ipcauto_dointvec_minmax(ctl_table *table, int write,
-       void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-       struct ctl_table ipc_table;
-       size_t lenp_bef = *lenp;
-       int oldval;
-       int rc;
-
-       memcpy(&ipc_table, table, sizeof(ipc_table));
-       ipc_table.data = get_ipc(table);
-       oldval = *((int *)(ipc_table.data));
-
-       rc = proc_dointvec_minmax(&ipc_table, write, buffer, lenp, ppos);
-
-       if (write && !rc && lenp_bef == *lenp) {
-               int newval = *((int *)(ipc_table.data));
-               /*
-                * The file "auto_msgmni" has correctly been set.
-                * React by (un)registering the corresponding tunable, if the
-                * value has changed.
-                */
-               if (newval != oldval)
-                       ipc_auto_callback(newval);
-       }
-
-       return rc;
-}
-
 #else
 #define proc_ipc_doulongvec_minmax NULL
 #define proc_ipc_dointvec         NULL
 #define proc_ipc_dointvec_minmax   NULL
 #define proc_ipc_dointvec_minmax_orphans   NULL
-#define proc_ipc_callback_dointvec_minmax  NULL
-#define proc_ipcauto_dointvec_minmax NULL
 #endif
 
 static int zero;
@@ -205,7 +129,7 @@ static struct ctl_table ipc_kern_table[] = {
                .data           = &init_ipc_ns.msg_ctlmni,
                .maxlen         = sizeof(init_ipc_ns.msg_ctlmni),
                .mode           = 0644,
-               .proc_handler   = proc_ipc_callback_dointvec_minmax,
+               .proc_handler   = proc_ipc_dointvec_minmax,
                .extra1         = &zero,
                .extra2         = &int_max,
        },
@@ -225,15 +149,6 @@ static struct ctl_table ipc_kern_table[] = {
                .mode           = 0644,
                .proc_handler   = proc_ipc_dointvec,
        },
-       {
-               .procname       = "auto_msgmni",
-               .data           = &init_ipc_ns.auto_msgmni,
-               .maxlen         = sizeof(int),
-               .mode           = 0644,
-               .proc_handler   = proc_ipcauto_dointvec_minmax,
-               .extra1         = &zero,
-               .extra2         = &one,
-       },
 #ifdef CONFIG_CHECKPOINT_RESTORE
        {
                .procname       = "sem_next_id",
diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c
deleted file mode 100644
index b9b31a4..0000000
--- a/ipc/ipcns_notifier.c
+++ /dev/null
@@ -1,92 +0,0 @@
-/*
- * linux/ipc/ipcns_notifier.c
- * Copyright (C) 2007 BULL SA. Nadia Derbey
- *
- * Notification mechanism for ipc namespaces:
- * The callback routine registered in the memory chain invokes the ipcns
- * notifier chain with the IPCNS_MEMCHANGED event.
- * Each callback routine registered in the ipcns namespace recomputes msgmni
- * for the owning namespace.
- */
-
-#include <linux/msg.h>
-#include <linux/rcupdate.h>
-#include <linux/notifier.h>
-#include <linux/nsproxy.h>
-#include <linux/ipc_namespace.h>
-
-#include "util.h"
-
-
-
-static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
-
-
-static int ipcns_callback(struct notifier_block *self,
-                               unsigned long action, void *arg)
-{
-       struct ipc_namespace *ns;
-
-       switch (action) {
-       case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */
-       case IPCNS_CREATED:
-       case IPCNS_REMOVED:
-               /*
-                * It's time to recompute msgmni
-                */
-               ns = container_of(self, struct ipc_namespace, ipcns_nb);
-               /*
-                * No need to get a reference on the ns: the 1st job of
-                * free_ipc_ns() is to unregister the callback routine.
-                * blocking_notifier_chain_unregister takes the wr lock to do
-                * it.
-                * When this callback routine is called the rd lock is held by
-                * blocking_notifier_call_chain.
-                * So the ipc ns cannot be freed while we are here.
-                */
-               recompute_msgmni(ns);
-               break;
-       default:
-               break;
-       }
-
-       return NOTIFY_OK;
-}
-
-int register_ipcns_notifier(struct ipc_namespace *ns)
-{
-       int rc;
-
-       memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
-       ns->ipcns_nb.notifier_call = ipcns_callback;
-       ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
-       rc = blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
-       if (!rc)
-               ns->auto_msgmni = 1;
-       return rc;
-}
-
-int cond_register_ipcns_notifier(struct ipc_namespace *ns)
-{
-       int rc;
-
-       memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
-       ns->ipcns_nb.notifier_call = ipcns_callback;
-       ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
-       rc = blocking_notifier_chain_cond_register(&ipcns_chain,
-                                                       &ns->ipcns_nb);
-       if (!rc)
-               ns->auto_msgmni = 1;
-       return rc;
-}
-
-void unregister_ipcns_notifier(struct ipc_namespace *ns)
-{
-       blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
-       ns->auto_msgmni = 0;
-}
-
-int ipcns_notify(unsigned long val)
-{
-       return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
-}
diff --git a/ipc/msg.c b/ipc/msg.c
index 6498531..ea7e0d1 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -76,43 +76,12 @@ static int newque(struct ipc_namespace *, struct ipc_params 
*);
 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);
+       ns->msg_ctlmni = MSGMNI;
 
        atomic_set(&ns->msg_bytes, 0);
        atomic_set(&ns->msg_hdrs, 0);
@@ -131,9 +100,6 @@ 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);
diff --git a/ipc/namespace.c b/ipc/namespace.c
index 59451c1..6c01c2a 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -45,14 +45,6 @@ static struct ipc_namespace *create_ipc_ns(struct 
user_namespace *user_ns,
        msg_init_ns(ns);
        shm_init_ns(ns);
 
-       /*
-        * msgmni has already been computed for the new ipc ns.
-        * Thus, do the ipcns creation notification before registering that
-        * new ipcns in the chain.
-        */
-       ipcns_notify(IPCNS_CREATED);
-       register_ipcns_notifier(ns);
-
        ns->user_ns = get_user_ns(user_ns);
 
        return ns;
@@ -99,25 +91,11 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids 
*ids,
 
 static void free_ipc_ns(struct ipc_namespace *ns)
 {
-       /*
-        * Unregistering the hotplug notifier at the beginning guarantees
-        * that the ipc namespace won't be freed while we are inside the
-        * callback routine. Since the blocking_notifier_chain_XXX routines
-        * hold a rw lock on the notifier list, unregister_ipcns_notifier()
-        * won't take the rw lock before blocking_notifier_call_chain() has
-        * released the rd lock.
-        */
-       unregister_ipcns_notifier(ns);
        sem_exit_ns(ns);
        msg_exit_ns(ns);
        shm_exit_ns(ns);
        atomic_dec(&nr_ipc_ns);
 
-       /*
-        * Do the ipcns removal notification after decrementing nr_ipc_ns in
-        * order to have a correct value when recomputing msgmni.
-        */
-       ipcns_notify(IPCNS_REMOVED);
        put_user_ns(ns->user_ns);
        proc_free_inum(ns->proc_inum);
        kfree(ns);
diff --git a/ipc/util.c b/ipc/util.c
index 2eb0d1e..768e1fc75 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -71,44 +71,6 @@ struct ipc_proc_iface {
        int (*show)(struct seq_file *, void *);
 };
 
-static void ipc_memory_notifier(struct work_struct *work)
-{
-       ipcns_notify(IPCNS_MEMCHANGED);
-}
-
-static int ipc_memory_callback(struct notifier_block *self,
-                               unsigned long action, void *arg)
-{
-       static DECLARE_WORK(ipc_memory_wq, ipc_memory_notifier);
-
-       switch (action) {
-       case MEM_ONLINE:    /* memory successfully brought online */
-       case MEM_OFFLINE:   /* or offline: it's time to recompute msgmni */
-               /*
-                * This is done by invoking the ipcns notifier chain with the
-                * IPC_MEMCHANGED event.
-                * In order not to keep the lock on the hotplug memory chain
-                * for too long, queue a work item that will, when waken up,
-                * activate the ipcns notification chain.
-                */
-               schedule_work(&ipc_memory_wq);
-               break;
-       case MEM_GOING_ONLINE:
-       case MEM_GOING_OFFLINE:
-       case MEM_CANCEL_ONLINE:
-       case MEM_CANCEL_OFFLINE:
-       default:
-               break;
-       }
-
-       return NOTIFY_OK;
-}
-
-static struct notifier_block ipc_memory_nb = {
-       .notifier_call = ipc_memory_callback,
-       .priority = IPC_CALLBACK_PRI,
-};
-
 /**
  * ipc_init - initialise ipc subsystem
  *
@@ -124,8 +86,6 @@ static int __init ipc_init(void)
        sem_init();
        msg_init();
        shm_init();
-       register_hotmemory_notifier(&ipc_memory_nb);
-       register_ipcns_notifier(&init_ipc_ns);
        return 0;
 }
 device_initcall(ipc_init);
-- 
1.9.3

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