From: Pierre Peiffer <[email-masked]>

This patch adds a new IPC_SETID command to the System V IPCs set of commands,
which allows to change the ID of an existing IPC.

This command can be used through the semctl/shmctl/msgctl API, with the new
ID passed as the third argument for msgctl and shmctl (instead of a pointer)
and through the fourth argument for semctl.

To be successful, the following rules must be respected:
- the IPC exists
- the user must be allowed to change the IPC attributes regarding the IPC
  permissions.
- the new ID must satisfy the ID computation rule.
- the entry (in the kernel internal table of IPCs) corresponding to the new
  ID must be free.

Signed-off-by: Pierre Peiffer <[email-masked]>
Acked-by: Serge Hallyn <[email-masked]>
---

 include/linux/ipc.h      |    9 +++++----
 ipc/compat.c             |    3 +++
 ipc/msg.c                |   27 ++++++++++++++++++++++++++-
 ipc/sem.c                |   27 ++++++++++++++++++++++++++-
 ipc/shm.c                |   27 ++++++++++++++++++++++++++-
 security/selinux/hooks.c |    3 +++
 6 files changed, 89 insertions(+), 7 deletions(-)

Index: b/include/linux/ipc.h
===================================================================
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -35,10 +35,11 @@ struct ipc_perm
  * Control commands used with semctl, msgctl and shmctl 
  * see also specific commands in sem.h, msg.h and shm.h
  */
-#define IPC_RMID 0     /* remove resource */
-#define IPC_SET  1     /* set ipc_perm options */
-#define IPC_STAT 2     /* get ipc_perm options */
-#define IPC_INFO 3     /* see ipcs */
+#define IPC_RMID   0     /* remove resource */
+#define IPC_SET    1     /* set ipc_perm options */
+#define IPC_STAT   2     /* get ipc_perm options */
+#define IPC_INFO   3     /* see ipcs */
+#define IPC_SETID  4     /* set ipc ID */
 
 /*
  * Version flags for semctl, msgctl, and shmctl commands
Index: b/ipc/compat.c
===================================================================
--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -253,6 +253,7 @@ long compat_sys_semctl(int first, int se
 	switch (third & (~IPC_64)) {
 	case IPC_INFO:
 	case IPC_RMID:
+	case IPC_SETID:
 	case SEM_INFO:
 	case GETVAL:
 	case GETPID:
@@ -425,6 +426,7 @@ long compat_sys_msgctl(int first, int se
 	switch (second & (~IPC_64)) {
 	case IPC_INFO:
 	case IPC_RMID:
+	case IPC_SETID:
 	case MSG_INFO:
 		err = sys_msgctl(first, second, uptr);
 		break;
@@ -597,6 +599,7 @@ long compat_sys_shmctl(int first, int se
 
 	switch (second & (~IPC_64)) {
 	case IPC_RMID:
+	case IPC_SETID:
 	case SHM_LOCK:
 	case SHM_UNLOCK:
 		err = sys_shmctl(first, second, uptr);
Index: b/ipc/msg.c
===================================================================
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -329,7 +329,8 @@ retry:
 	msg_unlock(msq);
 	up_write(&msg_ids(ns).rw_mutex);
 
-	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	/* msg_chid_nolock may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
 	if (err == -EAGAIN)
 		goto retry;
 
@@ -465,6 +466,9 @@ static int msgctl_down(struct ipc_namesp
 		 */
 		ss_wakeup(&msq->q_senders, 0);
 		break;
+	case IPC_SETID:
+		err = msg_chid_nolock(ns, msq, (int)(long)buf);
+		break;
 	default:
 		err = -EINVAL;
 	}
@@ -475,6 +479,24 @@ out_up:
 	return err;
 }
 
+static int msgctl_setid(struct ipc_namespace *ns, int msqid, int cmd,
+			struct msqid_ds __user *buf, int version)
+{
+	int err;
+retry:
+	err = idr_pre_get(&msg_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	err = msgctl_down(ns, msqid, cmd, buf, version);
+
+	/* msgctl_down may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
+	if (err == -EAGAIN)
+		goto retry;
+	return err;
+}
+
 asmlinkage long sys_msgctl(int msqid, int cmd, struct msqid_ds __user *buf)
 {
 	struct msg_queue *msq;
@@ -575,6 +597,9 @@ asmlinkage long sys_msgctl(int msqid, in
 	case IPC_RMID:
 		err = msgctl_down(ns, msqid, cmd, buf, version);
 		return err;
+	case IPC_SETID:
+		err = msgctl_setid(ns, msqid, cmd, buf, version);
+		return err;
 	default:
 		return  -EINVAL;
 	}
Index: b/ipc/sem.c
===================================================================
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -608,7 +608,8 @@ retry:
 	sem_unlock(sma);
 	up_write(&sem_ids(ns).rw_mutex);
 
-	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	/* sem_chid_nolock may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
 	if (err == -EAGAIN)
 		goto retry;
 
@@ -935,6 +936,9 @@ static int semctl_down(struct ipc_namesp
 		ipc_update_perm(&semid64.sem_perm, ipcp);
 		sma->sem_ctime = get_seconds();
 		break;
+	case IPC_SETID:
+		err = sem_chid_nolock(ns, sma, (int)arg.val);
+		break;
 	default:
 		err = -EINVAL;
 	}
@@ -946,6 +950,24 @@ out_up:
 	return err;
 }
 
+static int semctl_setid(struct ipc_namespace *ns,  int semid,
+			int cmd, int version, union semun arg)
+{
+	int err;
+retry:
+	err = idr_pre_get(&sem_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	err = semctl_down(ns, semid, cmd, version, arg);
+
+	/* semctl_down may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
+	if (err == -EAGAIN)
+		goto retry;
+	return err;
+}
+
 asmlinkage long sys_semctl (int semid, int semnum, int cmd, union semun arg)
 {
 	int err = -EINVAL;
@@ -978,6 +1000,9 @@ asmlinkage long sys_semctl (int semid, i
 	case IPC_SET:
 		err = semctl_down(ns, semid, cmd, version, arg);
 		return err;
+	case IPC_SETID:
+		err = semctl_setid(ns, semid, cmd, version, arg);
+		return err;
 	default:
 		return -EINVAL;
 	}
Index: b/ipc/shm.c
===================================================================
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -202,7 +202,8 @@ retry:
 	shm_unlock(shp);
 	up_write(&shm_ids(ns).rw_mutex);
 
-	/* ipc_chid may return -EAGAIN in case of memory requirement */
+	/* shm_chid_nolock may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
 	if (err == -EAGAIN)
 			goto retry;
 
@@ -679,6 +680,9 @@ static int shmctl_down(struct ipc_namesp
 		ipc_update_perm(&shmid64.shm_perm, ipcp);
 		shp->shm_ctim = get_seconds();
 		break;
+	case IPC_SETID:
+		err = shm_chid_nolock(ns, shp, (int)(long)buf);
+		break;
 	default:
 		err = -EINVAL;
 	}
@@ -689,6 +693,24 @@ out_up:
 	return err;
 }
 
+static int shmctl_setid(struct ipc_namespace *ns, int shmid, int cmd,
+			struct shmid_ds __user *buf, int version)
+{
+	int err;
+retry:
+	err = idr_pre_get(&shm_ids(ns).ipcs_idr, GFP_KERNEL);
+	if (!err)
+		return -ENOMEM;
+
+	err = shmctl_down(ns, shmid, cmd, buf, version);
+
+	/* shmctl_down may return -EAGAIN if there is no more free idr
+	   entry, just go and retry by filling again de idr cache */
+	if (err == -EAGAIN)
+		goto retry;
+	return err;
+}
+
 asmlinkage long sys_shmctl(int shmid, int cmd, struct shmid_ds __user *buf)
 {
 	struct shmid_kernel *shp;
@@ -850,6 +872,9 @@ asmlinkage long sys_shmctl(int shmid, in
 	case IPC_SET:
 		err = shmctl_down(ns, shmid, cmd, buf, version);
 		return err;
+	case IPC_SETID:
+		err = shmctl_setid(ns, shmid, cmd, buf, version);
+		return err;
 	default:
 		return -EINVAL;
 	}
Index: b/security/selinux/hooks.c
===================================================================
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4651,6 +4651,7 @@ static int selinux_msg_queue_msgctl(stru
 		perms = MSGQ__GETATTR | MSGQ__ASSOCIATE;
 		break;
 	case IPC_SET:
+	case IPC_SETID:
 		perms = MSGQ__SETATTR;
 		break;
 	case IPC_RMID:
@@ -4799,6 +4800,7 @@ static int selinux_shm_shmctl(struct shm
 		perms = SHM__GETATTR | SHM__ASSOCIATE;
 		break;
 	case IPC_SET:
+	case IPC_SETID:
 		perms = SHM__SETATTR;
 		break;
 	case SHM_LOCK:
@@ -4910,6 +4912,7 @@ static int selinux_sem_semctl(struct sem
 		perms = SEM__DESTROY;
 		break;
 	case IPC_SET:
+	case IPC_SETID:
 		perms = SEM__SETATTR;
 		break;
 	case IPC_STAT:

-- 
Pierre Peiffer
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