[PATCH 0/1] bcache patche for Linux v5.16-rc1

[PATCH 0/1] bcache patche for Linux v5.16-rc1

[Coly Li]

Hi Jens,

Here we have 1 patch from Lin Feng, which is a fix for his previous
patch which already picked in Linux v5.16 merge window.

Please take it, and thank you in advance.

Coly Li
---

Lin Feng (1):
  bcache: fix NULL pointer reference in cached_dev_detach_finish

 drivers/md/bcache/super.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

-- 
2.31.1

[PATCH 1/1] bcache: fix NULL pointer reference in cached_dev_detach_finish

[Coly Li]

From: Lin Feng <linf@wangsu.com>

Commit 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper
place on backing device detach") tries to fix calc_cached_dev_sectors
when bcache device detaches, but now we have:

cached_dev_detach_finish
    ...
    bcache_device_detach(&dc->disk);
        ...
        closure_put(&d->c->caching);
        d->c = NULL; [*explicitly set dc->disk.c to NULL*]
    list_move(&dc->list, &uncached_devices);
    calc_cached_dev_sectors(dc->disk.c); [*passing a NULL pointer*]
    ...

Upper codeflows shows how bug happens, this patch fix the problem by
caching dc->disk.c beforehand, and cache_set won't be freed under us
because c->caching closure at least holds a reference count and closure
callback __cache_set_unregister only being called by bch_cache_set_stop
which using closure_queue(&c->caching), that means c->caching closure
callback for destroying cache_set won't be trigger by previous
closure_put(&d->c->caching).
So at this stage(while cached_dev_detach_finish is calling) it's safe to
access cache_set dc->disk.c.

Fixes: 0259d4498ba4 ("bcache: move calc_cached_dev_sectors to proper place on backing device detach")
Signed-off-by: Lin Feng <linf@wangsu.com>
Signed-off-by: Coly Li <colyli@suse.de>
---
 drivers/md/bcache/super.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 86b9e355c583..140f35dc0c45 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1139,6 +1139,7 @@ static void cancel_writeback_rate_update_dwork(struct cached_dev *dc)
 static void cached_dev_detach_finish(struct work_struct *w)
 {
 	struct cached_dev *dc = container_of(w, struct cached_dev, detach);
+	struct cache_set *c = dc->disk.c;
 
 	BUG_ON(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags));
 	BUG_ON(refcount_read(&dc->count));
@@ -1156,7 +1157,7 @@ static void cached_dev_detach_finish(struct work_struct *w)
 
 	bcache_device_detach(&dc->disk);
 	list_move(&dc->list, &uncached_devices);
-	calc_cached_dev_sectors(dc->disk.c);
+	calc_cached_dev_sectors(c);
 
 	clear_bit(BCACHE_DEV_DETACHING, &dc->disk.flags);
 	clear_bit(BCACHE_DEV_UNLINK_DONE, &dc->disk.flags);
-- 
2.31.1

Re: [PATCH 0/1] bcache patche for Linux v5.16-rc1

[Jens Axboe]

On Fri, 12 Nov 2021 13:36:28 +0800, Coly Li wrote:
> Here we have 1 patch from Lin Feng, which is a fix for his previous
> patch which already picked in Linux v5.16 merge window.
> 
> Please take it, and thank you in advance.
> 
> Coly Li
> 
> [...]

Applied, thanks!

[1/1] bcache: fix NULL pointer reference in cached_dev_detach_finish
      commit: aa97f6cdb7e92909e17c8ca63e622fcb81d57a57

Best regards,
-- 
Jens Axboe