[PATCH RESEND v8 3/3] btrfs: fix suspicious RCU in BTRFS_IOC_DEV_INFO

Omar Sandoval
2015-01-09T20:36:38Z

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@osandov.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 7ca1cad..ee2528e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2706,6 +2706,7 @@ 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))
@@ -2726,17 +2727,16 @@ 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);
--
2.2.1