Right now, __list_add() code is repeated either in list.h or in list_debug.c, but only the debug checks are the different part. This extracts the checking into a separate function and consolidates __list_add(). Additionally this __list_add_debug() 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 <[email protected]> --- include/linux/list.h | 22 ++++++++++++++++------ lib/list_debug.c | 35 ++++++++++++++++++----------------- 2 files changed, 34 insertions(+), 23 deletions(-) diff --git a/include/linux/list.h b/include/linux/list.h index 5183138aa932..c38ff652ab59 100644 --- 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_debug(struct list_head *new, + struct list_head *prev, + struct list_head *next); +#else +static inline bool __list_add_debug(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_debug(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 3859bf63561c..5d78982eeb99 100644 --- a/lib/list_debug.c +++ b/lib/list_debug.c @@ -19,27 +19,28 @@ * the prev/next entries already! */ -void __list_add(struct list_head *new, +bool __list_add_debug(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_debug); void __list_del_entry(struct list_head *entry) { -- 2.7.4
