[PATCH] eCryptFS: mutex lock-unlock ordering fix

[PATCH] eCryptFS: mutex lock-unlock ordering fix

[Cyrill Gorcunov]

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 <gorcunov@gmail.com>
CC: Michael A. Halcrow <mhalcrow@us.ibm.com>
---

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.

Index: linux-2.6.git/fs/ecryptfs/miscdev.c
===================================================================
--- linux-2.6.git.orig/fs/ecryptfs/miscdev.c	2008-05-18 18:53:56.000000000 +0400
+++ linux-2.6.git/fs/ecryptfs/miscdev.c	2008-05-20 20:27:33.000000000 +0400
@@ -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;
 }
 

Re: [PATCH] eCryptFS: mutex lock-unlock ordering fix

[Cyrill Gorcunov]

[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 <gorcunov@gmail.com>
| CC: Michael A. Halcrow <mhalcrow@us.ibm.com>
| ---
| 
|  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 -