IB/hfi1: Ensure correct mm is used at all times

Two earlier bug fixes have created a security problem in the hfi1
driver. One fix aimed to solve an issue where current->mm was not valid
when closing the hfi1 cdev. It attempted to do this by saving a cached
value of the current->mm pointer at file open time. This is a problem if
another process with access to the FD calls in via write() or ioctl() to
pin pages via the hfi driver. The other fix tried to solve a use after
free by taking a reference on the mm.

To fix this correctly we use the existing cached value of the mm in the
mmu notifier. Now we can check in the insert, evict, etc. routines that
current->mm matched what the notifier was registered for. If not, then
don't allow access. The register of the mmu notifier will save the mm
pointer.

Since in do_exit() the exit_mm() is called before exit_files(), which
would call our close routine a reference is needed on the mm. We rely on
the mmgrab done by the registration of the notifier, whereas before it was
explicit. The mmu notifier deregistration happens when the user context is
torn down, the creation of which triggered the registration.

Also of note is we do not do any explicit work to protect the interval
tree notifier. It doesn't seem that this is going to be needed since we
aren't actually doing anything with current->mm. The interval tree
notifier stuff still has a FIXME noted from a previous commit that will be
addressed in a follow on patch.

Cc: <stable@vger.kernel.org>
Fixes: e0cf75deab81 ("IB/hfi1: Fix mm_struct use after free")
Fixes: 3faa3d9a308e ("IB/hfi1: Make use of mm consistent")
Link: https://lore.kernel.org/r/20201125210112.104301.51331.stgit@awfm-01.aw.intel.com
Suggested-by: Jann Horn <jannh@google.com>
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

1 files changed, 35 insertions, 33 deletions

diff --git a/drivers/infiniband/hw/hfi1/mmu_rb.c b/drivers/infiniband/hw/hfi1/mmu_rb.c
index 24ca17b77b72..f3fb28e3d5d7 100644
--- a/drivers/infiniband/hw/hfi1/mmu_rb.c
+++ b/drivers/infiniband/hw/hfi1/mmu_rb.c
@@ -1,4 +1,5 @@
 /*
+ * Copyright(c) 2020 Cornelis Networks, Inc.
  * Copyright(c) 2016 - 2017 Intel Corporation.
  *
  * This file is provided under a dual BSD/GPLv2 license.  When using or
@@ -48,23 +49,11 @@
 #include <linux/rculist.h>
 #include <linux/mmu_notifier.h>
 #include <linux/interval_tree_generic.h>
+#include <linux/sched/mm.h>
 
 #include "mmu_rb.h"
 #include "trace.h"
 
-struct mmu_rb_handler {
-	struct mmu_notifier mn;
-	struct rb_root_cached root;
-	void *ops_arg;
-	spinlock_t lock;        /* protect the RB tree */
-	struct mmu_rb_ops *ops;
-	struct mm_struct *mm;
-	struct list_head lru_list;
-	struct work_struct del_work;
-	struct list_head del_list;
-	struct workqueue_struct *wq;
-};
-
 static unsigned long mmu_node_start(struct mmu_rb_node *);
 static unsigned long mmu_node_last(struct mmu_rb_node *);
 static int mmu_notifier_range_start(struct mmu_notifier *,
@@ -92,37 +81,36 @@ static unsigned long mmu_node_last(struct mmu_rb_node *node)
 	return PAGE_ALIGN(node->addr + node->len) - 1;
 }
 
-int hfi1_mmu_rb_register(void *ops_arg, struct mm_struct *mm,
+int hfi1_mmu_rb_register(void *ops_arg,
 			 struct mmu_rb_ops *ops,
 			 struct workqueue_struct *wq,
 			 struct mmu_rb_handler **handler)
 {
-	struct mmu_rb_handler *handlr;
+	struct mmu_rb_handler *h;
 	int ret;
 
-	handlr = kmalloc(sizeof(*handlr), GFP_KERNEL);
-	if (!handlr)
+	h = kmalloc(sizeof(*h), GFP_KERNEL);
+	if (!h)
 		return -ENOMEM;
 
-	handlr->root = RB_ROOT_CACHED;
-	handlr->ops = ops;
-	handlr->ops_arg = ops_arg;
-	INIT_HLIST_NODE(&handlr->mn.hlist);
-	spin_lock_init(&handlr->lock);
-	handlr->mn.ops = &mn_opts;
-	handlr->mm = mm;
-	INIT_WORK(&handlr->del_work, handle_remove);
-	INIT_LIST_HEAD(&handlr->del_list);
-	INIT_LIST_HEAD(&handlr->lru_list);
-	handlr->wq = wq;
-
-	ret = mmu_notifier_register(&handlr->mn, handlr->mm);
+	h->root = RB_ROOT_CACHED;
+	h->ops = ops;
+	h->ops_arg = ops_arg;
+	INIT_HLIST_NODE(&h->mn.hlist);
+	spin_lock_init(&h->lock);
+	h->mn.ops = &mn_opts;
+	INIT_WORK(&h->del_work, handle_remove);
+	INIT_LIST_HEAD(&h->del_list);
+	INIT_LIST_HEAD(&h->lru_list);
+	h->wq = wq;
+
+	ret = mmu_notifier_register(&h->mn, current->mm);
 	if (ret) {
-		kfree(handlr);
+		kfree(h);
 		return ret;
 	}
 
-	*handler = handlr;
+	*handler = h;
 	return 0;
 }
 
@@ -134,7 +122,7 @@ void hfi1_mmu_rb_unregister(struct mmu_rb_handler *handler)
 	struct list_head del_list;
 
 	/* Unregister first so we don't get any more notifications. */
-	mmu_notifier_unregister(&handler->mn, handler->mm);
+	mmu_notifier_unregister(&handler->mn, handler->mn.mm);
 
 	/*
 	 * Make sure the wq delete handler is finished running.  It will not
@@ -166,6 +154,10 @@ int hfi1_mmu_rb_insert(struct mmu_rb_handler *handler,
 	int ret = 0;
 
 	trace_hfi1_mmu_rb_insert(mnode->addr, mnode->len);
+
+	if (current->mm != handler->mn.mm)
+		return -EPERM;
+
 	spin_lock_irqsave(&handler->lock, flags);
 	node = __mmu_rb_search(handler, mnode->addr, mnode->len);
 	if (node) {
@@ -180,6 +172,7 @@ int hfi1_mmu_rb_insert(struct mmu_rb_handler *handler,
 		__mmu_int_rb_remove(mnode, &handler->root);
 		list_del(&mnode->list); /* remove from LRU list */
 	}
+	mnode->handler = handler;
 unlock:
 	spin_unlock_irqrestore(&handler->lock, flags);
 	return ret;
@@ -217,6 +210,9 @@ bool hfi1_mmu_rb_remove_unless_exact(struct mmu_rb_handler *handler,
 	unsigned long flags;
 	bool ret = false;
 
+	if (current->mm != handler->mn.mm)
+		return ret;
+
 	spin_lock_irqsave(&handler->lock, flags);
 	node = __mmu_rb_search(handler, addr, len);
 	if (node) {
@@ -239,6 +235,9 @@ void hfi1_mmu_rb_evict(struct mmu_rb_handler *handler, void *evict_arg)
 	unsigned long flags;
 	bool stop = false;
 
+	if (current->mm != handler->mn.mm)
+		return;
+
 	INIT_LIST_HEAD(&del_list);
 
 	spin_lock_irqsave(&handler->lock, flags);
@@ -272,6 +271,9 @@ void hfi1_mmu_rb_remove(struct mmu_rb_handler *handler,
 {
 	unsigned long flags;
 
+	if (current->mm != handler->mn.mm)
+		return;
+
 	/* Validity of handler and node pointers has been checked by caller. */
 	trace_hfi1_mmu_rb_remove(node->addr, node->len);
 	spin_lock_irqsave(&handler->lock, flags);