[v6,04/10] ipc: add new SHM_SET command for sys_shmctl() call

New SHM_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/shm.h   |    1 +
 ipc/compat.c               |    1 +
 ipc/shm.c                  |   13 +++++++++++--
 security/selinux/hooks.c   |    1 +
 security/smack/smack_lsm.c |    1 +
 5 files changed, 15 insertions(+), 2 deletions(-)


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On Mon, 2012-10-15 at 19:59 +0400, Stanislav Kinsbursky wrote:
> New SHM_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.
[...]
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
[...]
> @@ -759,6 +763,10 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
>  	case IPC_RMID:
>  		do_shm_rmid(ns, ipcp);
>  		goto out_up;
> +	case SHM_SET:
> +		err = ipc_update_key(&shm_ids(ns), &shmid64.shm_perm, ipcp);
> +		if (err)
> +			break;
[...]

Please add /* fall through */ here, and in the similar cases in patches
5 and 7, to make clear that it's deliberate.

Ben.

Quoting Stanislav Kinsbursky (skinsbursky@parallels.com):
> New SHM_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>

Looks sane (modulo 'fallsthrough' comment already requested)

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

> ---
>  include/uapi/linux/shm.h   |    1 +
>  ipc/compat.c               |    1 +
>  ipc/shm.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/shm.h b/include/uapi/linux/shm.h
> index ec36fa1..d7413fd 100644
> --- a/include/uapi/linux/shm.h
> +++ b/include/uapi/linux/shm.h
> @@ -56,6 +56,7 @@ struct shmid_ds {
>  /* ipcs ctl commands */
>  #define SHM_STAT 	13
>  #define SHM_INFO 	14
> +#define SHM_SET		15
>  
>  /* Obsolete, used only for backwards compatibility */
>  struct	shminfo {
> diff --git a/ipc/compat.c b/ipc/compat.c
> index af30d13..35c750d 100644
> --- a/ipc/compat.c
> +++ b/ipc/compat.c
> @@ -692,6 +692,7 @@ long compat_sys_shmctl(int first, int second, void __user *uptr)
>  
>  
>  	case IPC_SET:
> +	case SHM_SET:
>  		if (version == IPC_64) {
>  			err = get_compat_shmid64_ds(&s64, uptr);
>  		} else {
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 80b0046..aebc50d 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -636,6 +636,9 @@ copy_shmid_from_user(struct shmid64_ds *out, void __user *buf, int version)
>  		out->shm_perm.uid	= tbuf_old.shm_perm.uid;
>  		out->shm_perm.gid	= tbuf_old.shm_perm.gid;
>  		out->shm_perm.mode	= tbuf_old.shm_perm.mode;
> +		out->shm_perm.cuid	= tbuf_old.shm_perm.cuid;
> +		out->shm_perm.cgid	= tbuf_old.shm_perm.cgid;
> +		out->shm_perm.key	= tbuf_old.shm_perm.key;
>  
>  		return 0;
>  	    }
> @@ -740,12 +743,13 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
>  	struct shmid_kernel *shp;
>  	int err;
>  
> -	if (cmd == IPC_SET) {
> +	if (cmd == IPC_SET || cmd == SHM_SET) {
>  		if (copy_shmid_from_user(&shmid64, buf, version))
>  			return -EFAULT;
>  	}
>  
> -	ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
> +	ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid,
> +			       (cmd != SHM_SET) ? cmd : IPC_SET,
>  			       &shmid64.shm_perm, 0);
>  	if (IS_ERR(ipcp))
>  		return PTR_ERR(ipcp);
> @@ -759,6 +763,10 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
>  	case IPC_RMID:
>  		do_shm_rmid(ns, ipcp);
>  		goto out_up;
> +	case SHM_SET:
> +		err = ipc_update_key(&shm_ids(ns), &shmid64.shm_perm, ipcp);
> +		if (err)
> +			break;
>  	case IPC_SET:
>  		err = ipc_update_perm(&shmid64.shm_perm, ipcp);
>  		if (err)
> @@ -938,6 +946,7 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
>  	}
>  	case IPC_RMID:
>  	case IPC_SET:
> +	case SHM_SET:
>  		err = shmctl_down(ns, shmid, cmd, buf, version);
>  		return err;
>  	default:
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 24ab414..62b2447 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -5027,6 +5027,7 @@ static int selinux_shm_shmctl(struct shmid_kernel *shp, int cmd)
>  		perms = SHM__GETATTR | SHM__ASSOCIATE;
>  		break;
>  	case IPC_SET:
> +	case SHM_SET:
>  		perms = SHM__SETATTR;
>  		break;
>  	case SHM_LOCK:
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 38be92c..c7eabc9 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2121,6 +2121,7 @@ static int smack_shm_shmctl(struct shmid_kernel *shp, int cmd)
>  		may = MAY_READ;
>  		break;
>  	case IPC_SET:
> +	case SHM_SET:
>  	case SHM_LOCK:
>  	case SHM_UNLOCK:
>  	case IPC_RMID:
> 
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