[v6,05/10] ipc: add new MSG_SET command for sys_msgctl() call

New MSG_SET command will be interpreted exactly as IPC_SET, but also will
update key, cuid and cgid values. IOW, it allows to change existent key value.
The fact, that key is not used is checked before update. Otherwise -EEXIST is
returned.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
 include/uapi/linux/msg.h   |    1 +
 ipc/compat.c               |    1 +
 ipc/msg.c                  |   13 +++++++++++--
 security/selinux/hooks.c   |    1 +
 security/smack/smack_lsm.c |    1 +
 5 files changed, 15 insertions(+), 2 deletions(-)


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Quoting Stanislav Kinsbursky (skinsbursky@parallels.com):
> New MSG_SET command will be interpreted exactly as IPC_SET, but also will
> update key, cuid and cgid values. IOW, it allows to change existent key value.
> The fact, that key is not used is checked before update. Otherwise -EEXIST is
> returned.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>

> ---
>  include/uapi/linux/msg.h   |    1 +
>  ipc/compat.c               |    1 +
>  ipc/msg.c                  |   13 +++++++++++--
>  security/selinux/hooks.c   |    1 +
>  security/smack/smack_lsm.c |    1 +
>  5 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/msg.h b/include/uapi/linux/msg.h
> index 78dbd2f..76999c9 100644
> --- a/include/uapi/linux/msg.h
> +++ b/include/uapi/linux/msg.h
> @@ -6,6 +6,7 @@
>  /* ipcs ctl commands */
>  #define MSG_STAT 11
>  #define MSG_INFO 12
> +#define MSG_SET  13
>  
>  /* msgrcv options */
>  #define MSG_NOERROR     010000  /* no error if message is too big */
> diff --git a/ipc/compat.c b/ipc/compat.c
> index 35c750d..9c70f9a 100644
> --- a/ipc/compat.c
> +++ b/ipc/compat.c
> @@ -483,6 +483,7 @@ long compat_sys_msgctl(int first, int second, void __user *uptr)
>  		break;
>  
>  	case IPC_SET:
> +	case MSG_SET:
>  		if (version == IPC_64) {
>  			err = get_compat_msqid64(&m64, uptr);
>  		} else {
> diff --git a/ipc/msg.c b/ipc/msg.c
> index 2f44946..68515dc 100644
> --- a/ipc/msg.c
> +++ b/ipc/msg.c
> @@ -392,6 +392,9 @@ copy_msqid_from_user(struct msqid64_ds *out, void __user *buf, int version)
>  		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;
> +		out->msg_perm.cuid	= tbuf_old.msg_perm.cuid;
> +		out->msg_perm.cgid	= tbuf_old.msg_perm.cgid;
> +		out->msg_perm.key	= tbuf_old.msg_perm.key;
>  
>  		if (tbuf_old.msg_qbytes == 0)
>  			out->msg_qbytes	= tbuf_old.msg_lqbytes;
> @@ -418,12 +421,13 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
>  	struct msg_queue *msq;
>  	int err;
>  
> -	if (cmd == IPC_SET) {
> +	if (cmd == IPC_SET || cmd == MSG_SET) {
>  		if (copy_msqid_from_user(&msqid64, buf, version))
>  			return -EFAULT;
>  	}
>  
> -	ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd,
> +	ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid,
> +			       (cmd != MSG_SET) ? cmd : IPC_SET,
>  			       &msqid64.msg_perm, msqid64.msg_qbytes);
>  	if (IS_ERR(ipcp))
>  		return PTR_ERR(ipcp);
> @@ -439,6 +443,7 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
>  		freeque(ns, ipcp);
>  		goto out_up;
>  	case IPC_SET:
> +	case MSG_SET:
>  		if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
>  		    !capable(CAP_SYS_RESOURCE)) {
>  			err = -EPERM;
> @@ -451,6 +456,9 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
>  
>  		msq->q_qbytes = msqid64.msg_qbytes;
>  
> +		if (cmd == MSG_SET)
> +			ipc_update_key(&msg_ids(ns), &msqid64.msg_perm, ipcp);
> +
>  		msq->q_ctime = get_seconds();
>  		/* sleeping receivers might be excluded by
>  		 * stricter permissions.
> @@ -569,6 +577,7 @@ SYSCALL_DEFINE3(msgctl, int, msqid, int, cmd, struct msqid_ds __user *, buf)
>  	}
>  	case IPC_SET:
>  	case IPC_RMID:
> +	case MSG_SET:
>  		err = msgctl_down(ns, msqid, cmd, buf, version);
>  		return err;
>  	default:
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 62b2447..78b77ac 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4885,6 +4885,7 @@ static int selinux_msg_queue_msgctl(struct msg_queue *msq, int cmd)
>  		perms = MSGQ__GETATTR | MSGQ__ASSOCIATE;
>  		break;
>  	case IPC_SET:
> +	case MSG_SET:
>  		perms = MSGQ__SETATTR;
>  		break;
>  	case IPC_RMID:
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index c7eabc9..d51a8da 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2374,6 +2374,7 @@ static int smack_msg_queue_msgctl(struct msg_queue *msq, int cmd)
>  		may = MAY_READ;
>  		break;
>  	case IPC_SET:
> +	case MSG_SET:
>  	case IPC_RMID:
>  		may = MAY_READWRITE;
>  		break;
> 
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