From 3a1407559a593d4360af12dd2df5296bf8eb0d28 Mon Sep 17 00:00:00 2001 From: Junichi Nomura Date: Wed, 27 May 2015 04:22:07 +0000 Subject: [PATCH] dm: fix NULL pointer when clone_and_map_rq returns !DM_MAPIO_REMAPPED When stacking request-based DM on blk_mq device, request cloning and remapping are done in a single call to target's clone_and_map_rq(). The clone is allocated and valid only if clone_and_map_rq() returns DM_MAPIO_REMAPPED. The "IS_ERR(clone)" check in map_request() does not cover all the !DM_MAPIO_REMAPPED cases that are possible (E.g. if underlying devices are not ready or unavailable, clone_and_map_rq() may return DM_MAPIO_REQUEUE without ever having established an ERR_PTR). Fix this by explicitly checking for a return that is not DM_MAPIO_REMAPPED in map_request(). Without this fix, DM core may call setup_clone() for a NULL clone and oops like this: BUG: unable to handle kernel NULL pointer dereference at 0000000000000068 IP: [] blk_rq_prep_clone+0x7d/0x137 ... CPU: 2 PID: 5793 Comm: kdmwork-253:3 Not tainted 4.0.0-nm #1 ... Call Trace: [] map_tio_request+0xa9/0x258 [dm_mod] [] kthread_worker_fn+0xfd/0x150 [] ? kthread_parkme+0x24/0x24 [] ? kthread_parkme+0x24/0x24 [] kthread+0xe6/0xee [] ? put_lock_stats+0xe/0x20 [] ? __init_kthread_worker+0x5b/0x5b [] ret_from_fork+0x58/0x90 [] ? __init_kthread_worker+0x5b/0x5b Fixes: e5863d9ad ("dm: allocate requests in target when stacking on blk-mq devices") Reported-by: Bart Van Assche Signed-off-by: Jun'ichi Nomura Signed-off-by: Mike Snitzer Cc: stable@vger.kernel.org # 4.0+ --- drivers/md/dm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 0bf79a0bad37..1c62ed8d09f4 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1972,8 +1972,8 @@ static int map_request(struct dm_rq_target_io *tio, struct request *rq, dm_kill_unmapped_request(rq, r); return r; } - if (IS_ERR(clone)) - return DM_MAPIO_REQUEUE; + if (r != DM_MAPIO_REMAPPED) + return r; if (setup_clone(clone, rq, tio, GFP_ATOMIC)) { /* -ENOMEM */ ti->type->release_clone_rq(clone); -- 2.20.1