From aa97f6cdb7e92909e17c8ca63e622fcb81d57a57 Mon Sep 17 00:00:00 2001 From: Lin Feng Date: Fri, 12 Nov 2021 13:36:29 +0800 Subject: bcache: fix NULL pointer reference in cached_dev_detach_finish 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 Signed-off-by: Coly Li Link: https://lore.kernel.org/r/20211112053629.3437-2-colyli@suse.de Signed-off-by: Jens Axboe --- drivers/md/bcache/super.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'drivers/md') 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); -- cgit v1.2.3