[PATCH v3 3/5] list: Split list_del() debug checking into separate function

Kees Cook
2016-08-17T21:42:26Z

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

Refactored from same hardening in PaX and Grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/list.h | 15 +++++++++------
lib/list_debug.c | 53 +++++++++++++++++++++++-----------------------------
2 files changed, 32 insertions(+), 36 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index 0ed58591538e..569c1cf80c64 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -32,6 +32,7 @@ static inline void INIT_LIST_HEAD(struct list_head *list)
extern bool __list_add_valid(struct list_head *new,
struct list_head *prev,
struct list_head *next);
+extern bool __list_del_entry_valid(struct list_head *entry);
#else
static inline bool __list_add_valid(struct list_head *new,
struct list_head *prev,
@@ -39,6 +40,10 @@ static inline bool __list_add_valid(struct list_head *new,
{
return true;
}
+static inline bool __list_del_entry_valid(struct list_head *entry)
+{
+ return true;
+}
#endif

/*
@@ -106,22 +111,20 @@ static inline void __list_del(struct list_head * prev, struct list_head * next)
* Note: list_empty() on entry does not return true after this, the entry is
* in an undefined state.
*/
-#ifndef CONFIG_DEBUG_LIST
static inline void __list_del_entry(struct list_head *entry)
{
+ if (!__list_del_entry_valid(entry))
+ return;
+
__list_del(entry->prev, entry->next);
}

static inline void list_del(struct list_head *entry)
{
- __list_del(entry->prev, entry->next);
+ __list_del_entry(entry);
entry->next = LIST_POISON1;
entry->prev = LIST_POISON2;
}
-#else
-extern void __list_del_entry(struct list_head *entry);
-extern void list_del(struct list_head *entry);
-#endif

/**
* list_replace - replace old entry by new one
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);
--
2.7.4