Commit 6446c684 authored Oct 13, 2017 by Liang Chen Committed by Jens Axboe Oct 16, 2017

bcache: safeguard a dangerous addressing in closure_queue



The use of the union reduces the size of closure struct by taking advantage
of the current size of its members. The offset of func in work_struct
equals the size of the first three members, so that work.work_func will
just reference the forth member - fn.

This is smart but dangerous. It can be broken if work_struct or the other
structs get changed, and can be a bit difficult to debug.

Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent a8500fc8

drivers/md/bcache/closure.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -251,6 +251,12 @@ static inline void set_closure_fn(struct closure cl, closure_fn fn,
		static inline void closure_queue(struct closure *cl)
		{
		struct workqueue_struct *wq = cl->wq;
		/**
		* Changes made to closure, work_struct, or a couple of other structs
		* may cause work.func not pointing to the right location.
		*/
		BUILD_BUG_ON(offsetof(struct closure, fn)
		!= offsetof(struct work_struct, func));
		if (wq) {
		INIT_WORK(&cl->work, cl->work.func);
		BUG_ON(!queue_work(wq, &cl->work));