[RFC PATCH 4/9] ntsync: Introduce NTSYNC_IOC_PUT_SEM.

[Elizabeth Figura <zfigura@xxxxxxxxxxxxxxx>]

This corresponds to the NT syscall NtReleaseSemaphore().

Signed-off-by: Elizabeth Figura <zfigura@xxxxxxxxxxxxxxx>
---
 drivers/misc/ntsync.c       | 76 +++++++++++++++++++++++++++++++++++++
 include/uapi/linux/ntsync.h |  2 +
 2 files changed, 78 insertions(+)

diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c
index 3287b94be351..d1c91c2a4f1a 100644
--- a/drivers/misc/ntsync.c
+++ b/drivers/misc/ntsync.c
@@ -21,9 +21,11 @@ enum ntsync_type {
 struct ntsync_obj {
 	struct rcu_head rhead;
 	struct kref refcount;
+	spinlock_t lock;
 
 	enum ntsync_type type;
 
+	/* The following fields are protected by the object lock. */
 	union {
 		struct {
 			__u32 count;
@@ -36,6 +38,19 @@ struct ntsync_device {
 	struct xarray objects;
 };
 
+static struct ntsync_obj *get_obj(struct ntsync_device *dev, __u32 id)
+{
+	struct ntsync_obj *obj;
+
+	rcu_read_lock();
+	obj = xa_load(&dev->objects, id);
+	if (obj && !kref_get_unless_zero(&obj->refcount))
+		obj = NULL;
+	rcu_read_unlock();
+
+	return obj;
+}
+
 static void destroy_obj(struct kref *ref)
 {
 	struct ntsync_obj *obj = container_of(ref, struct ntsync_obj, refcount);
@@ -48,6 +63,18 @@ static void put_obj(struct ntsync_obj *obj)
 	kref_put(&obj->refcount, destroy_obj);
 }
 
+static struct ntsync_obj *get_obj_typed(struct ntsync_device *dev, __u32 id,
+					enum ntsync_type type)
+{
+	struct ntsync_obj *obj = get_obj(dev, id);
+
+	if (obj && obj->type != type) {
+		put_obj(obj);
+		return NULL;
+	}
+	return obj;
+}
+
 static int ntsync_char_open(struct inode *inode, struct file *file)
 {
 	struct ntsync_device *dev;
@@ -81,6 +108,7 @@ static int ntsync_char_release(struct inode *inode, struct file *file)
 static void init_obj(struct ntsync_obj *obj)
 {
 	kref_init(&obj->refcount);
+	spin_lock_init(&obj->lock);
 }
 
 static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)
@@ -131,6 +159,52 @@ static int ntsync_delete(struct ntsync_device *dev, void __user *argp)
 	return 0;
 }
 
+/*
+ * Actually change the semaphore state, returning -EOVERFLOW if it is made
+ * invalid.
+ */
+static int put_sem_state(struct ntsync_obj *sem, __u32 count)
+{
+	lockdep_assert_held(&sem->lock);
+
+	if (sem->u.sem.count + count < sem->u.sem.count ||
+	    sem->u.sem.count + count > sem->u.sem.max)
+		return -EOVERFLOW;
+
+	sem->u.sem.count += count;
+	return 0;
+}
+
+static int ntsync_put_sem(struct ntsync_device *dev, void __user *argp)
+{
+	struct ntsync_sem_args __user *user_args = argp;
+	struct ntsync_sem_args args;
+	struct ntsync_obj *sem;
+	__u32 prev_count;
+	int ret;
+
+	if (copy_from_user(&args, argp, sizeof(args)))
+		return -EFAULT;
+
+	sem = get_obj_typed(dev, args.sem, NTSYNC_TYPE_SEM);
+	if (!sem)
+		return -EINVAL;
+
+	spin_lock(&sem->lock);
+
+	prev_count = sem->u.sem.count;
+	ret = put_sem_state(sem, args.count);
+
+	spin_unlock(&sem->lock);
+
+	put_obj(sem);
+
+	if (!ret && put_user(prev_count, &user_args->count))
+		ret = -EFAULT;
+
+	return ret;
+}
+
 static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
 			      unsigned long parm)
 {
@@ -142,6 +216,8 @@ static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
 		return ntsync_create_sem(dev, argp);
 	case NTSYNC_IOC_DELETE:
 		return ntsync_delete(dev, argp);
+	case NTSYNC_IOC_PUT_SEM:
+		return ntsync_put_sem(dev, argp);
 	default:
 		return -ENOIOCTLCMD;
 	}
diff --git a/include/uapi/linux/ntsync.h b/include/uapi/linux/ntsync.h
index d97afc138dcc..8c610d65f8ef 100644
--- a/include/uapi/linux/ntsync.h
+++ b/include/uapi/linux/ntsync.h
@@ -21,5 +21,7 @@ struct ntsync_sem_args {
 #define NTSYNC_IOC_CREATE_SEM		_IOWR(NTSYNC_IOC_BASE, 0, \
 					      struct ntsync_sem_args)
 #define NTSYNC_IOC_DELETE		_IOW (NTSYNC_IOC_BASE, 1, __u32)
+#define NTSYNC_IOC_PUT_SEM		_IOWR(NTSYNC_IOC_BASE, 2, \
+					      struct ntsync_sem_args)
 
 #endif
-- 
2.43.0