IB/uverbs: Fix locking around struct ib_uverbs_file ucontext

We have a parallel unlocked reader and writer with ib_uverbs_get_context()
vs everything else, and nothing guarantees this works properly.

Audit and fix all of the places that access ucontext to use one of the
following locking schemes:
- Call ib_uverbs_get_ucontext() under SRCU and check for failure
- Access the ucontext through an struct ib_uobject context member
  while holding a READ or WRITE lock on the uobject.
  This value cannot be NULL and has no race.
- Hold the ucontext_lock and check for ufile->ucontext !NULL

This also re-implements ib_uverbs_get_ucontext() in a way that is safe
against concurrent ib_uverbs_get_context() and disassociation.

As a side effect, every access to ucontext in the commands is via
ib_uverbs_get_context() with an error check, or via the uobject, so there
is no longer any need for the core code to check ucontext on every command
call. These checks are also removed.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/rdma_core.c

@@ -154,8 +154,14 @@ int __uobj_perform_destroy(const struct uverbs_obj_type *type, u32 id,
 static struct ib_uobject *alloc_uobj(struct ib_uverbs_file *ufile,
 				     const struct uverbs_obj_type *type)
 {
-	struct ib_uobject *uobj = kzalloc(type->obj_size, GFP_KERNEL);
+	struct ib_uobject *uobj;
+	struct ib_ucontext *ucontext;
+
+	ucontext = ib_uverbs_get_ucontext(ufile);
+	if (IS_ERR(ucontext))
+		return ERR_CAST(ucontext);
 
+	uobj = kzalloc(type->obj_size, GFP_KERNEL);
 	if (!uobj)
 		return ERR_PTR(-ENOMEM);
 	/*
@@ -163,7 +169,7 @@ static struct ib_uobject *alloc_uobj(struct ib_uverbs_file *ufile,
 	 * The object is added to the list in the commit stage.
 	 */
 	uobj->ufile = ufile;
-	uobj->context = ufile->ucontext;
+	uobj->context = ucontext;
 	INIT_LIST_HEAD(&uobj->list);
 	uobj->type = type;
 	/*
@@ -309,7 +315,7 @@ static struct ib_uobject *alloc_begin_idr_uobject(const struct uverbs_obj_type *
 	if (ret)
 		goto uobj_put;
 
-	ret = ib_rdmacg_try_charge(&uobj->cg_obj, ufile->ucontext->device,
+	ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
 				   RDMACG_RESOURCE_HCA_OBJECT);
 	if (ret)
 		goto idr_remove;
@@ -761,7 +767,7 @@ static void ufile_destroy_ucontext(struct ib_uverbs_file *ufile,
 	 * FIXME: Drivers are not permitted to fail dealloc_ucontext, remove
 	 * the error return.
 	 */
-	ret = ucontext->device->dealloc_ucontext(ufile->ucontext);
+	ret = ucontext->device->dealloc_ucontext(ucontext);
 	WARN_ON(ret);
 
 	ufile->ucontext = NULL;

drivers/infiniband/core/uverbs.h

@@ -137,8 +137,11 @@ struct ib_uverbs_completion_event_file {
 struct ib_uverbs_file {
 	struct kref				ref;
 	struct ib_uverbs_device		       *device;
-	/* Protects writing to ucontext */
 	struct mutex				ucontext_lock;
+	/*
+	 * ucontext must be accessed via ib_uverbs_get_ucontext() or with
+	 * ucontext_lock held
+	 */
 	struct ib_ucontext		       *ucontext;
 	struct ib_event_handler			event_handler;
 	struct ib_uverbs_async_event_file       *async_file;

drivers/infiniband/core/uverbs_cmd.c

@@ -146,10 +146,14 @@ ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
 		goto err_file;
 	}
 
-	file->ucontext = ucontext;
-
 	fd_install(resp.async_fd, filp);
 
+	/*
+	 * Make sure that ib_uverbs_get_ucontext() sees the pointer update
+	 * only after all writes to setup the ucontext have completed
+	 */
+	smp_store_release(&file->ucontext, ucontext);
+
 	mutex_unlock(&file->ucontext_lock);
 
 	return in_len;
@@ -350,7 +354,7 @@ ssize_t ib_uverbs_alloc_pd(struct ib_uverbs_file *file,
 	if (IS_ERR(uobj))
 		return PTR_ERR(uobj);
 
-	pd = ib_dev->alloc_pd(ib_dev, file->ucontext, &udata);
+	pd = ib_dev->alloc_pd(ib_dev, uobj->context, &udata);
 	if (IS_ERR(pd)) {
 		ret = PTR_ERR(pd);
 		goto err;
@@ -538,7 +542,7 @@ ssize_t ib_uverbs_open_xrcd(struct ib_uverbs_file *file,
 	}
 
 	if (!xrcd) {
-		xrcd = ib_dev->alloc_xrcd(ib_dev, file->ucontext, &udata);
+		xrcd = ib_dev->alloc_xrcd(ib_dev, obj->uobject.context, &udata);
 		if (IS_ERR(xrcd)) {
 			ret = PTR_ERR(xrcd);
 			goto err;
@@ -1004,7 +1008,7 @@ static struct ib_ucq_object *create_cq(struct ib_uverbs_file *file,
 	if (cmd_sz > offsetof(typeof(*cmd), flags) + sizeof(cmd->flags))
 		attr.flags = cmd->flags;
 
-	cq = ib_dev->create_cq(ib_dev, &attr, file->ucontext, uhw);
+	cq = ib_dev->create_cq(ib_dev, &attr, obj->uobject.context, uhw);
 	if (IS_ERR(cq)) {
 		ret = PTR_ERR(cq);
 		goto err_file;

drivers/infiniband/core/uverbs_ioctl.c

@@ -140,7 +140,7 @@ static int uverbs_process_attr(struct ib_uverbs_file *ufile,
 		if (uattr->attr_data.reserved)
 			return -EINVAL;
 
-		if (uattr->len != 0 || !ufile->ucontext)
+		if (uattr->len != 0)
 			return -EINVAL;
 
 		o_attr = &e->obj_attr;
@@ -373,9 +373,6 @@ static long ib_uverbs_cmd_verbs(struct ib_device *ib_dev,
 	if (!method_spec)
 		return -EPROTONOSUPPORT;
 
-	if ((method_spec->flags & UVERBS_ACTION_FLAG_CREATE_ROOT) ^ !file->ucontext)
-		return -EINVAL;
-
 	ctx_size = sizeof(*ctx) +
 		   sizeof(struct uverbs_attr_bundle) +
 		   sizeof(struct uverbs_attr_bundle_hash) * method_spec->num_buckets +

drivers/infiniband/core/uverbs_main.c

@@ -136,9 +136,27 @@ static int (*uverbs_ex_cmd_table[])(struct ib_uverbs_file *file,
 static void ib_uverbs_add_one(struct ib_device *device);
 static void ib_uverbs_remove_one(struct ib_device *device, void *client_data);
 
+/*
+ * Must be called with the ufile->device->disassociate_srcu held, and the lock
+ * must be held until use of the ucontext is finished.
+ */
 struct ib_ucontext *ib_uverbs_get_ucontext(struct ib_uverbs_file *ufile)
 {
-	return ufile->ucontext;
+	/*
+	 * We do not hold the hw_destroy_rwsem lock for this flow, instead
+	 * srcu is used. It does not matter if someone races this with
+	 * get_context, we get NULL or valid ucontext.
+	 */
+	struct ib_ucontext *ucontext = smp_load_acquire(&ufile->ucontext);
+
+	if (!srcu_dereference(ufile->device->ib_dev,
+			      &ufile->device->disassociate_srcu))
+		return ERR_PTR(-EIO);
+
+	if (!ucontext)
+		return ERR_PTR(-EINVAL);
+
+	return ucontext;
 }
 EXPORT_SYMBOL(ib_uverbs_get_ucontext);
 
@@ -729,10 +747,6 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 	if (ret)
 		return ret;
 
-	if (!file->ucontext &&
-	    (command != IB_USER_VERBS_CMD_GET_CONTEXT || extended))
-		return -EINVAL;
-
 	if (extended) {
 		if (count < (sizeof(hdr) + sizeof(ex_hdr)))
 			return -EINVAL;
@@ -791,22 +805,18 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct ib_uverbs_file *file = filp->private_data;
-	struct ib_device *ib_dev;
+	struct ib_ucontext *ucontext;
 	int ret = 0;
 	int srcu_key;
 
 	srcu_key = srcu_read_lock(&file->device->disassociate_srcu);
-	ib_dev = srcu_dereference(file->device->ib_dev,
-				  &file->device->disassociate_srcu);
-	if (!ib_dev) {
-		ret = -EIO;
+	ucontext = ib_uverbs_get_ucontext(file);
+	if (IS_ERR(ucontext)) {
+		ret = PTR_ERR(ucontext);
 		goto out;
 	}
 
-	if (!file->ucontext)
-		ret = -ENODEV;
-	else
-		ret = ib_dev->mmap(file->ucontext, vma);
+	ret = ucontext->device->mmap(ucontext, vma);
 out:
 	srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
 	return ret;

drivers/infiniband/core/uverbs_std_types_cq.c

@@ -113,7 +113,7 @@ static int UVERBS_HANDLER(UVERBS_METHOD_CQ_CREATE)(struct ib_device *ib_dev,
 	/* Temporary, only until drivers get the new uverbs_attr_bundle */
 	create_udata(attrs, &uhw);
 
-	cq = ib_dev->create_cq(ib_dev, &attr, file->ucontext, &uhw);
+	cq = ib_dev->create_cq(ib_dev, &attr, obj->uobject.context, &uhw);
 	if (IS_ERR(cq)) {
 		ret = PTR_ERR(cq);
 		goto err_event_file;

drivers/infiniband/core/uverbs_std_types_dm.c

@@ -70,7 +70,7 @@ static int UVERBS_HANDLER(UVERBS_METHOD_DM_ALLOC)(struct ib_device *ib_dev,
 
 	uobj = uverbs_attr_get(attrs, UVERBS_ATTR_ALLOC_DM_HANDLE)->obj_attr.uobject;
 
-	dm = ib_dev->alloc_dm(ib_dev, file->ucontext, &attr, attrs);
+	dm = ib_dev->alloc_dm(ib_dev, uobj->context, &attr, attrs);
 	if (IS_ERR(dm))
 		return PTR_ERR(dm);
 

drivers/infiniband/hw/mlx5/devx.c

@@ -458,16 +458,21 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_QUERY_UAR)(struct ib_device *ib_de
 				  struct ib_uverbs_file *file,
 				  struct uverbs_attr_bundle *attrs)
 {
-	struct mlx5_ib_ucontext *c = devx_ufile2uctx(file);
+	struct mlx5_ib_ucontext *c;
+	struct mlx5_ib_dev *dev;
 	u32 user_idx;
 	s32 dev_idx;
 
+	c = devx_ufile2uctx(file);
+	if (IS_ERR(c))
+		return PTR_ERR(c);
+	dev = to_mdev(c->ibucontext.device);
+
 	if (uverbs_copy_from(&user_idx, attrs,
 			     MLX5_IB_ATTR_DEVX_QUERY_UAR_USER_IDX))
 		return -EFAULT;
 
-	dev_idx = bfregn_to_uar_index(to_mdev(ib_dev),
-				      &c->bfregi, user_idx, true);
+	dev_idx = bfregn_to_uar_index(dev, &c->bfregi, user_idx, true);
 	if (dev_idx < 0)
 		return dev_idx;
 
@@ -482,8 +487,8 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_OTHER)(struct ib_device *ib_dev,
 				  struct ib_uverbs_file *file,
 				  struct uverbs_attr_bundle *attrs)
 {
-	struct mlx5_ib_ucontext *c = devx_ufile2uctx(file);
-	struct mlx5_ib_dev *dev = to_mdev(ib_dev);
+	struct mlx5_ib_ucontext *c;
+	struct mlx5_ib_dev *dev;
 	void *cmd_in = uverbs_attr_get_alloced_ptr(
 		attrs, MLX5_IB_ATTR_DEVX_OTHER_CMD_IN);
 	int cmd_out_len = uverbs_attr_get_len(attrs,
@@ -491,6 +496,11 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_DEVX_OTHER)(struct ib_device *ib_dev,
 	void *cmd_out;
 	int err;
 
+	c = devx_ufile2uctx(file);
+	if (IS_ERR(c))
+		return PTR_ERR(c);
+	dev = to_mdev(c->ibucontext.device);
+
 	if (!c->devx_uid)
 		return -EPERM;
 

include/rdma/uverbs_ioctl.h

@@ -123,14 +123,6 @@ struct uverbs_attr_spec_hash {
 struct uverbs_attr_bundle;
 struct ib_uverbs_file;
 
-enum {
-	/*
-	 * Action marked with this flag creates a context (or root for all
-	 * objects).
-	 */
-	UVERBS_ACTION_FLAG_CREATE_ROOT = 1U << 0,
-};
-
 struct uverbs_method_spec {
 	/* Combination of bits from enum UVERBS_ACTION_FLAG_XXXX */
 	u32						flags;