fix idr_find() locking
This is a patch that fixes the way idr_find() used to be called in ipc_lock():
in all the paths that don't imply an update of the ipcs idr, it was called
without the idr tree being locked.
The changes are:
. in ipc_ids, the mutex has been changed into a reader/writer semaphore.
. ipc_lock() now takes the mutex as a reader during the idr_find().
. a new routine ipc_lock_down() has been defined: it doesn't take the
mutex, assuming that it is being held by the caller. This is the routine
that is now called in all the update paths.
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
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 fd29246..b42fbd5 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -32,6 +32,7 @@
#include <linux/proc_fs.h>
#include <linux/audit.h>
#include <linux/nsproxy.h>
+#include <linux/rwsem.h>
#include <asm/unistd.h>
@@ -136,7 +137,7 @@
void ipc_init_ids(struct ipc_ids *ids)
{
- mutex_init(&ids->mutex);
+ init_rwsem(&ids->rw_mutex);
ids->in_use = 0;
ids->seq = 0;
@@ -191,7 +192,7 @@
* @ids: Identifier set
* @key: The key to find
*
- * Requires ipc_ids.mutex locked.
+ * 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
@@ -225,7 +226,7 @@
* ipc_get_maxid - get the last assigned id
* @ids: IPC identifier set
*
- * Called with ipc_ids.mutex held.
+ * Called with ipc_ids.rw_mutex held.
*/
int ipc_get_maxid(struct ipc_ids *ids)
@@ -263,7 +264,7 @@
* is returned. The 'new' entry is returned in a locked state on success.
* On failure the entry is not locked and -1 is returned.
*
- * Called with ipc_ids.mutex held.
+ * Called with ipc_ids.rw_mutex held as a writer.
*/
int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
@@ -316,9 +317,9 @@
if (!err)
return -ENOMEM;
- mutex_lock(&ids->mutex);
+ down_write(&ids->rw_mutex);
err = ops->getnew(ns, params);
- mutex_unlock(&ids->mutex);
+ up_write(&ids->rw_mutex);
return err;
}
@@ -335,7 +336,7 @@
*
* On success, the IPC id is returned.
*
- * It is called with ipc_ids.mutex and ipcp->lock held.
+ * It is called with ipc_ids.rw_mutex and ipcp->lock held.
*/
static int ipc_check_perms(struct kern_ipc_perm *ipcp, struct ipc_ops *ops,
struct ipc_params *params)
@@ -376,7 +377,11 @@
err = idr_pre_get(&ids->ipcs_idr, GFP_KERNEL);
- mutex_lock(&ids->mutex);
+ /*
+ * Take the lock as a writer since we are potentially going to add
+ * a new entry + read locks are not "upgradable"
+ */
+ down_write(&ids->rw_mutex);
ipcp = ipc_findkey(ids, params->key);
if (ipcp == NULL) {
/* key not used */
@@ -404,7 +409,7 @@
}
ipc_unlock(ipcp);
}
- mutex_unlock(&ids->mutex);
+ up_write(&ids->rw_mutex);
return err;
}
@@ -415,8 +420,8 @@
* @ids: IPC identifier set
* @ipcp: ipc perm structure containing the identifier to remove
*
- * ipc_ids.mutex and the spinlock for this ID are held before this
- * function is called, and remain locked on the exit.
+ * ipc_ids.rw_mutex (as a writer) and the spinlock for this ID are held
+ * before this function is called, and remain locked on the exit.
*/
void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
@@ -680,15 +685,17 @@
}
/**
- * ipc_lock - Lock an ipc structure
+ * ipc_lock - Lock an ipc structure without rw_mutex held
* @ids: IPC identifier set
* @id: ipc id to look for
*
* Look for an id in the ipc ids idr and lock the associated ipc object.
*
- * ipc_ids.mutex is not necessarily held before this function is called,
- * that's why we enter a RCU read section.
* The ipc object is locked on exit.
+ *
+ * This is the routine that should be called when the rw_mutex is not already
+ * held, i.e. idr tree not protected: it protects the idr tree in read mode
+ * during the idr_find().
*/
struct kern_ipc_perm *ipc_lock(struct ipc_ids *ids, int id)
@@ -696,13 +703,18 @@
struct kern_ipc_perm *out;
int lid = ipcid_to_idx(id);
+ down_read(&ids->rw_mutex);
+
rcu_read_lock();
out = idr_find(&ids->ipcs_idr, lid);
if (out == NULL) {
rcu_read_unlock();
+ up_read(&ids->rw_mutex);
return ERR_PTR(-EINVAL);
}
+ up_read(&ids->rw_mutex);
+
spin_lock(&out->lock);
/* ipc_rmid() may have already freed the ID while ipc_lock
@@ -717,6 +729,40 @@
return out;
}
+/**
+ * ipc_lock_down - Lock an ipc structure with rw_sem held
+ * @ids: IPC identifier set
+ * @id: ipc id to look for
+ *
+ * Look for an id in the ipc ids idr and lock the associated ipc object.
+ *
+ * The ipc object is locked on exit.
+ *
+ * This is the routine that should be called when the rw_mutex is already
+ * held, i.e. idr tree protected.
+ */
+
+struct kern_ipc_perm *ipc_lock_down(struct ipc_ids *ids, int id)
+{
+ struct kern_ipc_perm *out;
+ int lid = ipcid_to_idx(id);
+
+ rcu_read_lock();
+ out = idr_find(&ids->ipcs_idr, lid);
+ if (out == NULL) {
+ rcu_read_unlock();
+ return ERR_PTR(-EINVAL);
+ }
+
+ spin_lock(&out->lock);
+
+ /*
+ * No need to verify that the structure is still valid since the
+ * rw_mutex is held.
+ */
+ return out;
+}
+
#ifdef __ARCH_WANT_IPC_PARSE_VERSION
@@ -808,7 +854,7 @@
* Take the lock - this will be released by the corresponding
* call to stop().
*/
- mutex_lock(&ids->mutex);
+ down_read(&ids->rw_mutex);
/* pos < 0 is invalid */
if (*pos < 0)
@@ -835,7 +881,7 @@
ids = iter->ns->ids[iface->ids];
/* Release the lock we took in start() */
- mutex_unlock(&ids->mutex);
+ up_read(&ids->rw_mutex);
}
static int sysvipc_proc_show(struct seq_file *s, void *it)