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eCryptFS: mutex lock-unlock ordering fix

PATCH In review Cyrill Gorcunov 1 participant 2 messages May 20, 2008 Ecrypt file system

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Cyrill Gorcunov

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#0 lore raw

PATCH 1/1 eCryptFS: mutex lock-unlock ordering fix

We should lock/unlock mutexes by a proper way which means there should not be chains like ABAB but ABBA otherwise the race window is opened.

Signed-off-by Cyrill Gorcunov <[email protected]>
CC Michael A. Halcrow <[email protected]>

---

Michael, could you test it please? To be honest I see that my patch makes source looks ugly unfirtunelly... thoughts? Any comments are welcome. Maybe I missed something - but I think the chain LOCK: hash_mux -> mux, UNLOCK: hash_mux -> mux is a bit weird ;) so please check if I'm wrong.

fs/ecryptfs/miscdev.c +9 -6
Index: linux-2.6.git/fs/ecryptfs/miscdev.c
===================================================================
@@ -50,7 +50,6 @@ ecryptfs_miscdev_poll(struct file *file,
 					  current->nsproxy->user_ns);
 	BUG_ON(rc || !daemon);
 	mutex_lock(&daemon->mux);
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		printk(KERN_WARNING "%s: Attempt to poll on zombified "
 		       "daemon\n", __func__);

@@ -62,6 +61,7 @@ ecryptfs_miscdev_poll(struct file *file,
 		goto out_unlock_daemon;
 	daemon->flags |= ECRYPTFS_DAEMON_IN_POLL;
 	mutex_unlock(&daemon->mux);
+	mutex_unlock(&ecryptfs_daemon_hash_mux);
 	poll_wait(file, &daemon->wait, pt);
 	mutex_lock(&daemon->mux);
 	if (!list_empty(&daemon->msg_ctx_out_queue))

@@ -69,6 +69,8 @@ ecryptfs_miscdev_poll(struct file *file,
 out_unlock_daemon:
 	daemon->flags &= ~ECRYPTFS_DAEMON_IN_POLL;
 	mutex_unlock(&daemon->mux);
+	if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
+		mutex_unlock(&ecryptfs_daemon_hash_mux);
 	return mask;
 }
 

@@ -257,24 +259,23 @@ ecryptfs_miscdev_read(struct file *file,
 	mutex_lock(&daemon->mux);
 	if (daemon->flags & ECRYPTFS_DAEMON_ZOMBIE) {
 		rc = 0;
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
 		printk(KERN_WARNING "%s: Attempt to read from zombified "
 		       "daemon\n", __func__);
 		goto out_unlock_daemon;
 	}
 	if (daemon->flags & ECRYPTFS_DAEMON_IN_READ) {
 		rc = 0;
-		mutex_unlock(&ecryptfs_daemon_hash_mux);
 		goto out_unlock_daemon;
 	}
 	/* This daemon will not go away so long as this flag is set */
 	daemon->flags |= ECRYPTFS_DAEMON_IN_READ;
-	mutex_unlock(&ecryptfs_daemon_hash_mux);
 check_list:
 	if (list_empty(&daemon->msg_ctx_out_queue)) {
+		if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
+			mutex_unlock(&ecryptfs_daemon_hash_mux);
 		mutex_unlock(&daemon->mux);
-		rc = wait_event_interruptible(
-			daemon->wait, !list_empty(&daemon->msg_ctx_out_queue));
+		rc = wait_event_interruptible(daemon->wait,
+			!list_empty(&daemon->msg_ctx_out_queue));
 		mutex_lock(&daemon->mux);
 		if (rc < 0) {
 			rc = 0;

@@ -357,6 +358,8 @@ out_unlock_msg_ctx:
 out_unlock_daemon:
 	daemon->flags &= ~ECRYPTFS_DAEMON_IN_READ;
 	mutex_unlock(&daemon->mux);
+	if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
+		mutex_unlock(&ecryptfs_daemon_hash_mux);
 	return rc;
 }
author
#1 lore raw

[Cyrill Gorcunov - Tue, May 20, 2008 at 08:39:28PM +0400]

| We should lock/unlock mutexes by a proper way which means
| there should not be chains like ABAB but ABBA otherwise the
| race window is opened.
| 
| Signed-off-by: Cyrill Gorcunov <[email protected]>
| CC: Michael A. Halcrow <[email protected]>
| ---
| 
|  check_list:
[...]
|  	if (list_empty(&daemon->msg_ctx_out_queue)) {
NIT ---> | +		if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
| +			mutex_unlock(&ecryptfs_daemon_hash_mux);
|  		mutex_unlock(&daemon->mux);
| -		rc = wait_event_interruptible(
| -			daemon->wait, !list_empty(&daemon->msg_ctx_out_queue));
| +		rc = wait_event_interruptible(daemon->wait,
| +			!list_empty(&daemon->msg_ctx_out_queue));
|  		mutex_lock(&daemon->mux);
|  		if (rc < 0) {
|  			rc = 0;
| @@ -357,6 +358,8 @@ out_unlock_msg_ctx:
|  out_unlock_daemon:
|  	daemon->flags &= ~ECRYPTFS_DAEMON_IN_READ;
|  	mutex_unlock(&daemon->mux);
| +	if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
| +		mutex_unlock(&ecryptfs_daemon_hash_mux);
|  	return rc;
|  }
|

It's a bit wrong (could release mutex being ack'ed by another thread) will fix - please DROP this patch. Sorry!

- Cyrill -