[RFC PATCH 19/21] list_bl: Extend integrity checking to cover the same cases as 'hlist'

[Will Deacon]

The list integrity checks for 'hlist_bl' are missing a number of cases
that are covered by other list implementations (e.g. 'hlist'), such as
validating 'next' and 'pprev' pointers when adding and deleting nodes.

Extend the list_bl integrity checks to bring them up to the same level
as for other list implementations.

Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
 lib/list_debug.c | 48 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 40 insertions(+), 8 deletions(-)

diff --git a/lib/list_debug.c b/lib/list_debug.c
index 9591fa6c9337..3be50b5c8014 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -7,6 +7,7 @@
 
 #include <linux/export.h>
 #include <linux/list.h>
+#include <linux/list_bl.h>
 #include <linux/bug.h>
 #include <linux/kernel.h>
 #include <linux/rculist.h>
@@ -190,27 +191,58 @@ EXPORT_SYMBOL(__hlist_nulls_del_valid);
 bool __hlist_bl_add_head_valid(struct hlist_bl_node *new,
 			       struct hlist_bl_head *head)
 {
+	struct hlist_bl_node *first = hlist_bl_first(head);
 	unsigned long hlock = (unsigned long)head->first & LIST_BL_LOCKMASK;
 	unsigned long nlock = (unsigned long)new & LIST_BL_LOCKMASK;
 
-	return !(CHECK_DATA_CORRUPTION(nlock,
+	if (CHECK_DATA_CORRUPTION(nlock,
 			"hlist_bl_add_head: node is locked\n") ||
-		 CHECK_DATA_CORRUPTION(hlock != LIST_BL_LOCKMASK,
-			"hlist_bl_add_head: head is unlocked\n"));
+	    CHECK_DATA_CORRUPTION(hlock != LIST_BL_LOCKMASK,
+			"hlist_bl_add_head: head is unlocked\n"))
+		return false;
+
+	if (CHECK_DATA_CORRUPTION(first && first->pprev != &head->first,
+			"hlist_bl_add_head corruption: first->pprev should be &head->first (%px), but was %px (first=%px)",
+			&head->first, first->pprev, first) ||
+	    CHECK_DATA_CORRUPTION(new == first,
+			"hlist_bl_add_head double add: new (%px) == first (%px)",
+			new, first))
+		return false;
+
+	return true;
 }
 EXPORT_SYMBOL(__hlist_bl_add_head_valid);
 
 bool __hlist_bl_del_valid(struct hlist_bl_node *node)
 {
+	struct hlist_bl_node *prev, *next = node->next;
 	unsigned long nlock = (unsigned long)node & LIST_BL_LOCKMASK;
+	unsigned long pnext;
 
-	return !(CHECK_DATA_CORRUPTION(nlock,
-			"hlist_bl_del_valid: node locked") ||
-		 CHECK_DATA_CORRUPTION(node->next == LIST_POISON1,
+	if (CHECK_DATA_CORRUPTION(nlock,
+			"hlist_bl_del corruption: node is locked") ||
+	    CHECK_DATA_CORRUPTION(next == LIST_POISON1,
 			"hlist_bl_del corruption, %px->next is LIST_POISON1 (%px)\n",
 			node, LIST_POISON1) ||
-		 CHECK_DATA_CORRUPTION(node->pprev == LIST_POISON2,
+	    CHECK_DATA_CORRUPTION(node->pprev == LIST_POISON2,
 			"hlist_bl_del corruption, %px->pprev is LIST_POISON2 (%px)\n",
-			node, LIST_POISON2));
+			node, LIST_POISON2))
+		return false;
+
+	BUILD_BUG_ON(offsetof(struct hlist_bl_node, next) !=
+		     offsetof(struct hlist_bl_head, first));
+	prev = container_of(node->pprev, struct hlist_bl_node, next);
+	pnext = (unsigned long)prev->next & ~LIST_BL_LOCKMASK;
+	if (CHECK_DATA_CORRUPTION((unsigned long)next & LIST_BL_LOCKMASK,
+			"hlist_bl_del_corruption: node->next is locked") ||
+	    CHECK_DATA_CORRUPTION((struct hlist_bl_node *)pnext != node,
+			"hlist_bl_del corruption: prev->next should be %px, but was %lx\n",
+			node, pnext) ||
+	    CHECK_DATA_CORRUPTION(next && next->pprev != &node->next,
+			"hlist_bl_del corruption: next->pprev should be %px, but was %px\n",
+			&node->next, next->pprev))
+		return false;
+
+	return true;
 }
 EXPORT_SYMBOL(__hlist_bl_del_valid);
-- 
2.20.1