Commit d7c81673 authored by Kees Cook's avatar Kees Cook Committed by Paul E. McKenney
Browse files

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: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
parent 1001354c

include/linux/list.h

+16 −6
Original line number Diff line number Diff line
@@ -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

lib/list_debug.c

+23 −25
Original line number Diff line number Diff line
@@ -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,

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",

	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);

	WARN(prev->next != next,

		"list_add corruption. prev->next should be "

		"next (%p), but was %p. (prev=%p).\n",

		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);

	WARN(new == prev || new == next,

	     "list_add double add: new=%p, prev=%p, next=%p.\n",

		return false;

	}

	if (unlikely(new == prev || new == next)) {

		WARN(1, "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);

		return false;

	}

	return true;

}

EXPORT_SYMBOL(__list_add);

EXPORT_SYMBOL(__list_add_valid);



void __list_del_entry(struct list_head *entry)

{

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