ipc: move locking out of ipcctl_pre_down_nolock
This function currently acquires both the rw_mutex and the rcu lock on
successful lookups, leaving the callers to explicitly unlock them,
creating another two level locking situation.
Make the callers (including those that still use ipcctl_pre_down())
explicitly lock and unlock the rwsem and rcu lock.
Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/util.c b/ipc/util.c
index 399821a..a0c139f 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -746,8 +746,10 @@
* It must be called without any lock held and
* - retrieves the ipc with the given id in the given table.
* - performs some audit and permission check, depending on the given cmd
- * - returns the ipc with both ipc and rw_mutex locks held in case of success
+ * - returns the ipc with the ipc lock held in case of success
* or an err-code without any lock held otherwise.
+ *
+ * Call holding the both the rw_mutex and the rcu read lock.
*/
struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
struct ipc_ids *ids, int id, int cmd,
@@ -772,13 +774,10 @@
int err = -EPERM;
struct kern_ipc_perm *ipcp;
- down_write(&ids->rw_mutex);
- rcu_read_lock();
-
ipcp = ipc_obtain_object_check(ids, id);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
- goto out_up;
+ goto err;
}
audit_ipc_obj(ipcp);
@@ -789,16 +788,8 @@
euid = current_euid();
if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid) ||
ns_capable(ns->user_ns, CAP_SYS_ADMIN))
- return ipcp;
-
-out_up:
- /*
- * Unsuccessful lookup, unlock and return
- * the corresponding error.
- */
- rcu_read_unlock();
- up_write(&ids->rw_mutex);
-
+ return ipcp; /* successful lookup */
+err:
return ERR_PTR(err);
}