linux-kernel - [PATCH v8 3/3] btrfs: fix suspicious RCU in BTRFS_IOC_DEV

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Message-Id: <77dcc43b8e3dd20b1994b8e978008800e8dcf6b7.1418007402.git.osandov@osandov.com>
Date:	Sun,  7 Dec 2014 19:40:59 -0800
From:	Omar Sandoval <osandov@...ndov.com>
To:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	Joe Perches <joe@...ches.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org
Cc:	Omar Sandoval <osandov@...ndov.com>
Subject: [PATCH v8 3/3] btrfs: fix suspicious RCU in BTRFS_IOC_DEV_INFO

A naked read of the value of an RCU pointer isn't safe. Put the whole
access in an RCU critical section, not just the pointer dereference.

Signed-off-by: Omar Sandoval <osandov@...ndov.com>
---
 fs/btrfs/ioctl.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 9ebc3cc..324be12 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2734,6 +2734,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
 	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
 	int ret = 0;
 	char *s_uuid = NULL;
+	struct rcu_string *name;
 
 	di_args = memdup_user(arg, sizeof(*di_args));
 	if (IS_ERR(di_args))
@@ -2754,17 +2755,16 @@ static long btrfs_ioctl_dev_info(struct btrfs_root *root, void __user *arg)
 	di_args->bytes_used = btrfs_device_get_bytes_used(dev);
 	di_args->total_bytes = btrfs_device_get_total_bytes(dev);
 	memcpy(di_args->uuid, dev->uuid, sizeof(di_args->uuid));
-	if (dev->name) {
-		struct rcu_string *name;
 
-		rcu_read_lock();
-		name = rcu_dereference(dev->name);
+	rcu_read_lock();
+	name = rcu_dereference(dev->name);
+	if (name) {
 		strncpy(di_args->path, name->str, sizeof(di_args->path));
-		rcu_read_unlock();
 		di_args->path[sizeof(di_args->path) - 1] = 0;
 	} else {
 		di_args->path[0] = '\0';
 	}
+	rcu_read_unlock();
 
 out:
 	mutex_unlock(&fs_devices->device_list_mutex);
-- 
2.1.3

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