From 43e43c9ea60a7a1831ec823773e924d2dadefd44 Mon Sep 17 00:00:00 2001 From: Junichi Nomura Date: Tue, 17 Nov 2015 09:36:56 +0000 Subject: [PATCH] dm mpath: fix infinite recursion in ioctl when no paths and !queue_if_no_path In multipath_prepare_ioctl(), - pgpath is a path selected from available paths - m->queue_io is true if we cannot send a request immediately to paths, either because: * there is no available path * the path group needs activation (pg_init) - pg_init is not started - pg_init is still running - m->queue_if_no_path is true if the device is configured to queue I/O if there are no available paths If !pgpath && !m->queue_if_no_path, the handler should return -EIO. However in the course of refactoring the condition check has broken and returns success in that case. Since bdev points to the dm device itself, dm_blk_ioctl() calls __blk_dev_driver_ioctl() for itself and recurses until crash. You could reproduce the problem like this: # dmsetup create mp --table '0 1024 multipath 0 0 0 0' # sg_inq /dev/mapper/mp [ 172.648615] BUG: unable to handle kernel paging request at fffffffc81b10268 [ 172.662843] PGD 19dd067 PUD 0 [ 172.666269] Thread overran stack, or stack corrupted [ 172.671808] Oops: 0000 [#1] SMP ... Fix the condition check with some clarifications. Fixes: e56f81e0b01e ("dm: refactor ioctl handling") Signed-off-by: Jun'ichi Nomura Cc: Christoph Hellwig Cc: Mike Snitzer Signed-off-by: Mike Snitzer --- drivers/md/dm-mpath.c | 28 +++++++++++++++------------- 1 file changed, 15 insertions(+), 13 deletions(-) diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c index 3d1829237678..cfa29f574c2a 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -1537,29 +1537,31 @@ static int multipath_prepare_ioctl(struct dm_target *ti, struct block_device **bdev, fmode_t *mode) { struct multipath *m = ti->private; - struct pgpath *pgpath; unsigned long flags; int r; - r = 0; - spin_lock_irqsave(&m->lock, flags); if (!m->current_pgpath) __choose_pgpath(m, 0); - pgpath = m->current_pgpath; - - if (pgpath) { - *bdev = pgpath->path.dev->bdev; - *mode = pgpath->path.dev->mode; + if (m->current_pgpath) { + if (!m->queue_io) { + *bdev = m->current_pgpath->path.dev->bdev; + *mode = m->current_pgpath->path.dev->mode; + r = 0; + } else { + /* pg_init has not started or completed */ + r = -ENOTCONN; + } + } else { + /* No path is available */ + if (m->queue_if_no_path) + r = -ENOTCONN; + else + r = -EIO; } - if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path)) - r = -ENOTCONN; - else if (!*bdev) - r = -EIO; - spin_unlock_irqrestore(&m->lock, flags); if (r == -ENOTCONN) { -- 2.20.1