[PATCH 5.3 064/135] nvme-multipath: fix crash in nvme_mpath_clear_ctrl_paths

Greg Kroah-Hartman
2019-12-03T22:41:59Z

From: Anton Eidelman <anton@lightbitslabs.com>

[ Upstream commit 763303a83a095a88c3a8a0d1abf97165db2e8bf5 ]

nvme_mpath_clear_ctrl_paths() iterates through
the ctrl->namespaces list while holding ctrl->scan_lock.
This does not seem to be the correct way of protecting
from concurrent list modification.

Specifically, nvme_scan_work() sorts ctrl->namespaces
AFTER unlocking scan_lock.

This may result in the following (rare) crash in ctrl disconnect
during scan_work:

BUG: kernel NULL pointer dereference, address: 0000000000000050
Oops: 0000 [#1] SMP PTI
CPU: 0 PID: 3995 Comm: nvme 5.3.5-050305-generic
RIP: 0010:nvme_mpath_clear_current_path+0xe/0x90 [nvme_core]
...
Call Trace:
nvme_mpath_clear_ctrl_paths+0x3c/0x70 [nvme_core]
nvme_remove_namespaces+0x35/0xe0 [nvme_core]
nvme_do_delete_ctrl+0x47/0x90 [nvme_core]
nvme_sysfs_delete+0x49/0x60 [nvme_core]
dev_attr_store+0x17/0x30
sysfs_kf_write+0x3e/0x50
kernfs_fop_write+0x11e/0x1a0
__vfs_write+0x1b/0x40
vfs_write+0xb9/0x1a0
ksys_write+0x67/0xe0
__x64_sys_write+0x1a/0x20
do_syscall_64+0x5a/0x130
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f8d02bfb154

Fix:
After taking scan_lock in nvme_mpath_clear_ctrl_paths()
down_read(&ctrl->namespaces_rwsem) as well to make list traversal safe.
This will not cause deadlocks because taking scan_lock never happens
while holding the namespaces_rwsem.
Moreover, scan work downs namespaces_rwsem in the same order.

Alternative: sort ctrl->namespaces in nvme_scan_work()
while still holding the scan_lock.
This would leave nvme_mpath_clear_ctrl_paths() without correct protection
against ctrl->namespaces modification by anyone other than scan_work.

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anton Eidelman <anton@lightbitslabs.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/nvme/host/multipath.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index d320684d25b20..a5c809c85f6d2 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -158,9 +158,11 @@ void nvme_mpath_clear_ctrl_paths(struct nvme_ctrl *ctrl)
struct nvme_ns *ns;

mutex_lock(&ctrl->scan_lock);
+ down_read(&ctrl->namespaces_rwsem);
list_for_each_entry(ns, &ctrl->namespaces, list)
if (nvme_mpath_clear_current_path(ns))
kblockd_schedule_work(&ns->head->requeue_work);
+ up_read(&ctrl->namespaces_rwsem);
mutex_unlock(&ctrl->scan_lock);
}

--
2.20.1