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Message-Id: <1368666490-29055-5-git-send-email-davidlohr.bueso@hp.com>
Date: Wed, 15 May 2013 18:08:03 -0700
From: Davidlohr Bueso <davidlohr.bueso@...com>
To: akpm@...ux-foundation.org
Cc: torvalds@...ux-foundation.org, riel@...hat.com,
linux-kernel@...r.kernel.org,
Davidlohr Bueso <davidlohr.bueso@...com>
Subject: [PATCH 04/11] 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@...com>
---
ipc/msg.c | 24 +++++++++++++++++-------
ipc/sem.c | 27 ++++++++++++++++-----------
ipc/shm.c | 23 +++++++++++++++++------
ipc/util.c | 21 ++++++---------------
4 files changed, 56 insertions(+), 39 deletions(-)
diff --git a/ipc/msg.c b/ipc/msg.c
index 7a6f344..4eaeb08 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -409,31 +409,38 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
return -EFAULT;
}
+ down_write(&msg_ids(ns).rw_mutex);
+ rcu_read_lock();
+
ipcp = ipcctl_pre_down(ns, &msg_ids(ns), msqid, cmd,
&msqid64.msg_perm, msqid64.msg_qbytes);
- if (IS_ERR(ipcp))
- return PTR_ERR(ipcp);
+ if (IS_ERR(ipcp)) {
+ err = PTR_ERR(ipcp);
+ /* the ipc lock is not held upon failure */
+ goto out_unlock1;
+ }
msq = container_of(ipcp, struct msg_queue, q_perm);
err = security_msg_queue_msgctl(msq, cmd);
if (err)
- goto out_unlock;
+ goto out_unlock0;
switch (cmd) {
case IPC_RMID:
+ /* freeque unlocks the ipc object and rcu */
freeque(ns, ipcp);
goto out_up;
case IPC_SET:
if (msqid64.msg_qbytes > ns->msg_ctlmnb &&
!capable(CAP_SYS_RESOURCE)) {
err = -EPERM;
- goto out_unlock;
+ goto out_unlock0;
}
err = ipc_update_perm(&msqid64.msg_perm, ipcp);
if (err)
- goto out_unlock;
+ goto out_unlock0;
msq->q_qbytes = msqid64.msg_qbytes;
@@ -450,8 +457,11 @@ static int msgctl_down(struct ipc_namespace *ns, int msqid, int cmd,
default:
err = -EINVAL;
}
-out_unlock:
- msg_unlock(msq);
+
+out_unlock0:
+ ipc_unlock_object(&msq->q_perm);
+out_unlock1:
+ rcu_read_unlock();
out_up:
up_write(&msg_ids(ns).rw_mutex);
return err;
diff --git a/ipc/sem.c b/ipc/sem.c
index 7854fc8..f7d99f9 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1274,39 +1274,44 @@ static int semctl_down(struct ipc_namespace *ns, int semid,
return -EFAULT;
}
+ down_write(&sem_ids(ns).rw_mutex);
+ rcu_read_lock();
+
ipcp = ipcctl_pre_down_nolock(ns, &sem_ids(ns), semid, cmd,
&semid64.sem_perm, 0);
- if (IS_ERR(ipcp))
- return PTR_ERR(ipcp);
+ if (IS_ERR(ipcp)) {
+ err = PTR_ERR(ipcp);
+ /* the ipc lock is not held upon failure */
+ goto out_unlock1;
+ }
sma = container_of(ipcp, struct sem_array, sem_perm);
err = security_sem_semctl(sma, cmd);
- if (err) {
- rcu_read_unlock();
- goto out_up;
- }
+ if (err)
+ goto out_unlock1;
- switch(cmd){
+ switch (cmd) {
case IPC_RMID:
sem_lock(sma, NULL, -1);
+ /* freeary unlocks the ipc object and rcu */
freeary(ns, ipcp);
goto out_up;
case IPC_SET:
sem_lock(sma, NULL, -1);
err = ipc_update_perm(&semid64.sem_perm, ipcp);
if (err)
- goto out_unlock;
+ goto out_unlock0;
sma->sem_ctime = get_seconds();
break;
default:
- rcu_read_unlock();
err = -EINVAL;
- goto out_up;
+ goto out_unlock1;
}
-out_unlock:
+out_unlock0:
sem_unlock(sma, -1);
+out_unlock1:
rcu_read_unlock();
out_up:
up_write(&sem_ids(ns).rw_mutex);
diff --git a/ipc/shm.c b/ipc/shm.c
index 1fd3d05f..078cc19 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -759,31 +759,42 @@ static int shmctl_down(struct ipc_namespace *ns, int shmid, int cmd,
return -EFAULT;
}
+ down_write(&shm_ids(ns).rw_mutex);
+ rcu_read_lock();
+
ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
&shmid64.shm_perm, 0);
- if (IS_ERR(ipcp))
- return PTR_ERR(ipcp);
+ if (IS_ERR(ipcp)) {
+ err = PTR_ERR(ipcp);
+ /* the ipc lock is not held upon failure */
+ goto out_unlock1;
+ }
shp = container_of(ipcp, struct shmid_kernel, shm_perm);
err = security_shm_shmctl(shp, cmd);
if (err)
- goto out_unlock;
+ goto out_unlock0;
+
switch (cmd) {
case IPC_RMID:
+ /* do_shm_rmid unlocks the ipc object and rcu */
do_shm_rmid(ns, ipcp);
goto out_up;
case IPC_SET:
err = ipc_update_perm(&shmid64.shm_perm, ipcp);
if (err)
- goto out_unlock;
+ goto out_unlock0;
shp->shm_ctim = get_seconds();
break;
default:
err = -EINVAL;
}
-out_unlock:
- shm_unlock(shp);
+
+out_unlock0:
+ ipc_unlock_object(&shp->shm_perm);
+out_unlock1:
+ rcu_read_unlock();
out_up:
up_write(&shm_ids(ns).rw_mutex);
return err;
diff --git a/ipc/util.c b/ipc/util.c
index 92f0242..a746abb 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -745,8 +745,10 @@ int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out)
* 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,
@@ -771,13 +773,10 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
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);
@@ -788,16 +787,8 @@ struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
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);
}
--
1.7.11.7
--
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