[PATCH 2/5] 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 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>

---
 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 845a287..43f3596 100644
--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -138,6 +138,9 @@ 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;
 }
 
@@ -149,6 +152,9 @@ 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..7b1a2d8 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 (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,