[PATCH v4 3/9] ipc: segment key change helper introduced

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

This patch introduces existent segment key changing infrastructure.
New function ipc_update_key() can be used change segment key, cuid, cgid
values. It checks for that new key is not used (except IPC_PRIVATE) prior to
set it on existent.
To make this possible, added copying of this fields from user-space in
__get_compat_ipc_perm() and __get_compat_ipc64_perm() functions. Also segment
search by key and lock were splitted into different functions, because
ipc_update_key() doesn't need to lock the segment during check that new key is
not used.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
 ipc/compat.c |    6 ++++++
 ipc/util.c   |   51 ++++++++++++++++++++++++++++++++++++++++++++++++---
 ipc/util.h   |    2 ++
 3 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/ipc/compat.c b/ipc/compat.c
index a6df704..aa88515 100644
--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -144,6 +144,9 @@ static inline int __get_compat_ipc64_perm(struct ipc64_perm *p64,
 	err  = __get_user(p64->uid, &up64->uid);
 	err |= __get_user(p64->gid, &up64->gid);
 	err |= __get_user(p64->mode, &up64->mode);
+	err |= __get_user(p64->cuid, &up64->cuid);
+	err |= __get_user(p64->cgid, &up64->cgid);
+	err |= __get_user(p64->key, &up64->key);
 	return err;
 }
 
@@ -155,6 +158,9 @@ static inline int __get_compat_ipc_perm(struct ipc64_perm *p,
 	err  = __get_user(p->uid, &up->uid);
 	err |= __get_user(p->gid, &up->gid);
 	err |= __get_user(p->mode, &up->mode);
+	err |= __get_user(p->cuid, &up->cuid);
+	err |= __get_user(p->cgid, &up->cgid);
+	err |= __get_user(p->key, &up->key);
 	return err;
 }
 
diff --git a/ipc/util.c b/ipc/util.c
index ac9c6a9..d1e2f25 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -173,7 +173,7 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
  *	@key: The key to find
  *	
  *	Requires ipc_ids.rw_mutex locked.
- *	Returns the LOCKED pointer to the ipc structure if found or NULL
+ *	Returns the UNLOCKED pointer to the ipc structure if found or NULL
  *	if not.
  *	If key is found ipc points to the owning ipc structure
  */
@@ -195,7 +195,6 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
 			continue;
 		}
 
-		ipc_lock_by_ptr(ipc);
 		return ipc;
 	}
 
@@ -203,6 +202,27 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
 }
 
 /**
+ *	ipc_findkey_locked	-	find and lock a key in an ipc identifier set
+ *	@ids: Identifier set
+ *	@key: The key to find
+ *
+ *	Requires ipc_ids.rw_mutex locked.
+ *	Returns the LOCKED pointer to the ipc structure if found or NULL
+ *	if not.
+ *	If key is found ipc points to the owning ipc structure
+ */
+
+static struct kern_ipc_perm *ipc_findkey_locked(struct ipc_ids *ids, key_t key)
+{
+	struct kern_ipc_perm *ipc;
+
+	ipc = ipc_findkey(ids, key);
+	if (ipc)
+		ipc_lock_by_ptr(ipc);
+	return ipc;
+}
+
+/**
  *	ipc_get_maxid 	-	get the last assigned id
  *	@ids: IPC identifier set
  *
@@ -382,7 +402,7 @@ retry:
 	 * a new entry + read locks are not "upgradable"
 	 */
 	down_write(&ids->rw_mutex);
-	ipcp = ipc_findkey(ids, params->key);
+	ipcp = ipc_findkey_locked(ids, params->key);
 	if (ipcp == NULL) {
 		/* key not used */
 		if (!(flg & IPC_CREAT))
@@ -749,6 +769,31 @@ int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
 }
 
 /**
+ * ipc_update_key - update the key of an IPC.
+ * @in:  the permission given as input.
+ * @out: the permission of the ipc to set.
+ *
+ * Common routine called by sys_shmctl(), sys_semctl(). sys_msgctl().
+ */
+int ipc_update_key(struct ipc_ids *ids, struct ipc64_perm *in,
+		    struct kern_ipc_perm *out)
+{
+
+	if (in->key && out->key != in->key) {
+		/*
+		 * Check for existent segment with the same key.
+		 * Note: ipc_ids.rw_mutex is taken for write already.
+		 */
+		if (ipc_findkey(ids, in->key))
+			return -EEXIST;
+	}
+	out->cuid = in->cuid;
+	out->cgid = in->cgid;
+	out->key = in->key;
+	return 0;
+}
+
+/**
  * ipc_update_perm - update the permissions of an IPC.
  * @in:  the permission given as input.
  * @out: the permission of the ipc to set.
diff --git a/ipc/util.h b/ipc/util.h
index 5f04b02..2bc6a9a 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -126,6 +126,8 @@ struct kern_ipc_perm *ipc_lock(struct ipc_ids *, int);
 
 void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);
 void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out);
+int ipc_update_key(struct ipc_ids *ids, struct ipc64_perm *in,
+		   struct kern_ipc_perm *out);
 void ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out);
 struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
 				      struct ipc_ids *ids, int id, int cmd,