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Subject[PATCH] bcache: safeguard a dangerous addressing in closure_queue
Date
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>
---
Replacing all occurences of closure_fn to work_func_fn seems to be an option
but that would end up with a big lenghty and error prone patch.

drivers/md/bcache/closure.h | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/md/bcache/closure.h b/drivers/md/bcache/closure.h
index 295b7e4..dbff8f4 100644
--- a/drivers/md/bcache/closure.h
+++ b/drivers/md/bcache/closure.h
@@ -251,6 +251,11 @@ 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.
+ */
+ BUG_ON((unsigned long)cl->fn != (unsigned long)cl->work.func);
if (wq) {
INIT_WORK(&cl->work, cl->work.func);
BUG_ON(!queue_work(wq, &cl->work));
--
1.8.3.1
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