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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>
This commit is contained in:
Liang Chen 2017-10-13 16:35:40 -07:00 committed by Jens Axboe
parent a8500fc816
commit 6446c684f9
1 changed files with 6 additions and 0 deletions
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6
drivers/md/bcache/closure.h
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@ -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));