From d7c816733d501b59dbdc2483f2cc8e4431fd9160 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 Aug 2016 14:42:08 -0700 Subject: 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 Acked-by: Steven Rostedt Signed-off-by: Paul E. McKenney Acked-by: Rik van Riel --- lib/list_debug.c | 48 +++++++++++++++++++++++------------------------- 1 file changed, 23 insertions(+), 25 deletions(-) (limited to 'lib/list_debug.c') diff --git a/lib/list_debug.c b/lib/list_debug.c index 3859bf63561c..149dd57b583b 100644 --- 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 @@ -13,33 +12,32 @@ #include /* - * 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) { -- cgit v1.2.3