list: Split list_add() debug checking into separate function

Right now, __list_add() code is repeated either in list.h or in
list_debug.c, but the only differences between the two versions
are the debug checks. This commit therefore extracts these debug
checks into a separate __list_add_valid() function and consolidates
__list_add(). Additionally this new __list_add_valid() function will stop
list manipulations if a corruption is detected, instead of allowing for
further corruption that may lead to even worse conditions.

This is slight refactoring of the same hardening done in PaX and Grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>

diff --git a/include/linux/list.h b/include/linux/list.h
index 5809e9a2de5b23939eef9dbf1653f7df299a7240..b6da9b1dce4d92feb786ea8c5f9557d0626f0ee7 100644 (file)
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -28,27 +28,37 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
        list->prev = list;
 }
 
+#ifdef CONFIG_DEBUG_LIST
+extern bool __list_add_valid(struct list_head *new,
+                             struct list_head *prev,
+                             struct list_head *next);
+#else
+static inline bool __list_add_valid(struct list_head *new,
+                               struct list_head *prev,
+                               struct list_head *next)
+{
+       return true;
+}
+#endif
+
 /*
  * Insert a new entry between two known consecutive entries.
  *
  * This is only for internal list manipulation where we know
  * the prev/next entries already!
  */
-#ifndef CONFIG_DEBUG_LIST
 static inline void __list_add(struct list_head *new,
                              struct list_head *prev,
                              struct list_head *next)
 {
+       if (!__list_add_valid(new, prev, next))
+               return;
+
        next->prev = new;
        new->next = next;
        new->prev = prev;
        WRITE_ONCE(prev->next, new);
 }
-#else
-extern void __list_add(struct list_head *new,
-                             struct list_head *prev,
-                             struct list_head *next);
-#endif
 
 /**
  * list_add - add a new entry

diff --git a/lib/list_debug.c b/lib/list_debug.c
index 3859bf63561c63936947b007fe3ee20e822509a1..149dd57b583b7243a632ce9cf315254407fc47c7 100644 (file)
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -2,8 +2,7 @@
  * Copyright 2006, Red Hat, Inc., Dave Jones
  * Released under the General Public License (GPL).
  *
- * This file contains the linked list implementations for
- * DEBUG_LIST.
+ * This file contains the linked list validation for DEBUG_LIST.
  */
 
 #include <linux/export.h>
@@ -13,33 +12,32 @@
 #include <linux/rculist.h>
 
 /*
- * Insert a new entry between two known consecutive entries.
- *
- * This is only for internal list manipulation where we know
- * the prev/next entries already!
+ * Check that the data structures for the list manipulations are reasonably
+ * valid. Failures here indicate memory corruption (and possibly an exploit
+ * attempt).
  */
 
-void __list_add(struct list_head *new,
-                             struct list_head *prev,
-                             struct list_head *next)
+bool __list_add_valid(struct list_head *new, struct list_head *prev,
+                     struct list_head *next)
 {
-       WARN(next->prev != prev,
-               "list_add corruption. next->prev should be "
-               "prev (%p), but was %p. (next=%p).\n",
-               prev, next->prev, next);
-       WARN(prev->next != next,
-               "list_add corruption. prev->next should be "
-               "next (%p), but was %p. (prev=%p).\n",
-               next, prev->next, prev);
-       WARN(new == prev || new == next,
-            "list_add double add: new=%p, prev=%p, next=%p.\n",
-            new, prev, next);
-       next->prev = new;
-       new->next = next;
-       new->prev = prev;
-       WRITE_ONCE(prev->next, new);
+       if (unlikely(next->prev != prev)) {
+               WARN(1, "list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
+                       prev, next->prev, next);
+               return false;
+       }
+       if (unlikely(prev->next != next)) {
+               WARN(1, "list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
+                       next, prev->next, prev);
+               return false;
+       }
+       if (unlikely(new == prev || new == next)) {
+               WARN(1, "list_add double add: new=%p, prev=%p, next=%p.\n",
+                       new, prev, next);
+               return false;
+       }
+       return true;
 }
-EXPORT_SYMBOL(__list_add);
+EXPORT_SYMBOL(__list_add_valid);
 
 void __list_del_entry(struct list_head *entry)
 {