linux-kernel - [PATCH 1/2] of: of_node_get()/of_node

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Message-Id: <1544769771-5468-2-git-send-email-frowand.list@gmail.com>
Date:   Thu, 13 Dec 2018 22:42:50 -0800
From:   frowand.list@...il.com
To:     robh+dt@...nel.org, Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        Thomas Falcon <tlfalcon@...ux.vnet.ibm.com>,
        Juliet Kim <minkim@...ibm.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] of: of_node_get()/of_node_put() nodes held in phandle cache

From: Frank Rowand <frank.rowand@...y.com>

The phandle cache contains struct device_node pointers.  The refcount
of the pointers was not incremented while in the cache, allowing use
after free error after kfree() of the node.  Add the proper increment
and decrement of the use count.

Fixes: 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")

Signed-off-by: Frank Rowand <frank.rowand@...y.com>
---

do not "cc: stable", unless the following commits are also in stable:

  commit e54192b48da7 ("of: fix phandle cache creation for DTs with no phandles")
  commit b9952b5218ad ("of: overlay: update phandle cache on overlay apply and remove")
  commit 0b3ce78e90fc ("of: cache phandle nodes to reduce cost of of_find_node_by_phandle()")

 drivers/of/base.c | 70 ++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 46 insertions(+), 24 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 09692c9b32a7..d599367cb92a 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -116,9 +116,6 @@ int __weak of_node_to_nid(struct device_node *np)
 }
 #endif
 
-static struct device_node **phandle_cache;
-static u32 phandle_cache_mask;
-
 /*
  * Assumptions behind phandle_cache implementation:
  *   - phandle property values are in a contiguous range of 1..n
@@ -127,6 +124,44 @@ int __weak of_node_to_nid(struct device_node *np)
  *   - the phandle lookup overhead reduction provided by the cache
  *     will likely be less
  */
+
+static struct device_node **phandle_cache;
+static u32 phandle_cache_mask;
+
+/*
+ * Caller must hold devtree_lock.
+ */
+void __of_free_phandle_cache(void)
+{
+	u32 cache_entries = phandle_cache_mask + 1;
+	u32 k;
+
+	if (!phandle_cache)
+		return;
+
+	for (k = 0; k < cache_entries; k++)
+		of_node_put(phandle_cache[k]);
+
+	kfree(phandle_cache);
+	phandle_cache = NULL;
+}
+
+int of_free_phandle_cache(void)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&devtree_lock, flags);
+
+	__of_free_phandle_cache();
+
+	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+
+	return 0;
+}
+#if !defined(CONFIG_MODULES)
+late_initcall_sync(of_free_phandle_cache);
+#endif
+
 void of_populate_phandle_cache(void)
 {
 	unsigned long flags;
@@ -136,8 +171,7 @@ void of_populate_phandle_cache(void)
 
 	raw_spin_lock_irqsave(&devtree_lock, flags);
 
-	kfree(phandle_cache);
-	phandle_cache = NULL;
+	__of_free_phandle_cache();
 
 	for_each_of_allnodes(np)
 		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
@@ -155,30 +189,15 @@ void of_populate_phandle_cache(void)
 		goto out;
 
 	for_each_of_allnodes(np)
-		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
+		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL) {
+			of_node_get(np);
 			phandle_cache[np->phandle & phandle_cache_mask] = np;
+		}
 
 out:
 	raw_spin_unlock_irqrestore(&devtree_lock, flags);
 }
 
-int of_free_phandle_cache(void)
-{
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&devtree_lock, flags);
-
-	kfree(phandle_cache);
-	phandle_cache = NULL;
-
-	raw_spin_unlock_irqrestore(&devtree_lock, flags);
-
-	return 0;
-}
-#if !defined(CONFIG_MODULES)
-late_initcall_sync(of_free_phandle_cache);
-#endif
-
 void __init of_core_init(void)
 {
 	struct device_node *np;
@@ -1195,8 +1214,11 @@ struct device_node *of_find_node_by_phandle(phandle handle)
 	if (!np) {
 		for_each_of_allnodes(np)
 			if (np->phandle == handle) {
-				if (phandle_cache)
+				if (phandle_cache) {
+					/* will put when removed from cache */
+					of_node_get(np);
 					phandle_cache[masked_handle] = np;
+				}
 				break;
 			}
 	}
-- 
Frank Rowand <frank.rowand@...y.com>