list: Split list_del() debug checking into separate function

Similar to the list_add() debug consolidation, this commit consolidates
the debug checking performed during CONFIG_DEBUG_LIST into a new
__list_del_entry_valid() function, and stops list updates when corruption
is found.

Refactored from same hardening 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>

1 files changed, 23 insertions, 30 deletions

diff --git a/lib/list_debug.c b/lib/list_debug.c
index d0b89b9d0736..276565fca2a6 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -39,41 +39,34 @@ bool __list_add_valid(struct list_head *new, struct list_head *prev,
 }
 EXPORT_SYMBOL(__list_add_valid);
 
-void __list_del_entry(struct list_head *entry)
+bool __list_del_entry_valid(struct list_head *entry)
 {
         struct list_head *prev, *next;
 
         prev = entry->prev;
         next = entry->next;
 
-        if (WARN(next == LIST_POISON1,
-                "list_del corruption, %p->next is LIST_POISON1 (%p)\n",
-                entry, LIST_POISON1) ||
-            WARN(prev == LIST_POISON2,
-                "list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
-                entry, LIST_POISON2) ||
-            WARN(prev->next != entry,
-                "list_del corruption. prev->next should be %p, "
-                "but was %p\n", entry, prev->next) ||
-            WARN(next->prev != entry,
-                "list_del corruption. next->prev should be %p, "
-                "but was %p\n", entry, next->prev))
-                return;
-
-        __list_del(prev, next);
-}
-EXPORT_SYMBOL(__list_del_entry);
+        if (unlikely(next == LIST_POISON1)) {
+                WARN(1, "list_del corruption, %p->next is LIST_POISON1 (%p)\n",
+                        entry, LIST_POISON1);
+                return false;
+        }
+        if (unlikely(prev == LIST_POISON2)) {
+                WARN(1, "list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
+                        entry, LIST_POISON2);
+                return false;
+        }
+        if (unlikely(prev->next != entry)) {
+                WARN(1, "list_del corruption. prev->next should be %p, but was %p\n",
+                        entry, prev->next);
+                return false;
+        }
+        if (unlikely(next->prev != entry)) {
+                WARN(1, "list_del corruption. next->prev should be %p, but was %p\n",
+                        entry, next->prev);
+                return false;
+        }
+        return true;
 
-/**
- * list_del - deletes entry from list.
- * @entry: the element to delete from the list.
- * Note: list_empty on entry does not return true after this, the entry is
- * in an undefined state.
- */
-void list_del(struct list_head *entry)
-{
-        __list_del_entry(entry);
-        entry->next = LIST_POISON1;
-        entry->prev = LIST_POISON2;
 }
-EXPORT_SYMBOL(list_del);
+EXPORT_SYMBOL(__list_del_entry_valid);