[PATCH] nvme-fc: fix double free of fabrics options when nvme_add_ctrl() fails

[Niklas Cassel <cassel@kernel.org>]

nvmf_create_ctrl() owns the fabrics options and frees them whenever
->create_ctrl() returns an error, so a transport must not free them on
its own error paths.  nvme-fc tracks this by testing ctrl->ctrl.opts in
nvme_fc_ctrl_free(), which requires nvme_fc_init_ctrl() to clear that
pointer on every error exit.

The coupling is implicit, and commit 1a9e218195a5 ("nvme: split device
add from initialization") broke it by adding a second error exit.  When
nvme_add_ctrl() fails, nvme_fc_init_ctrl() jumps to out_put_ctrl:, past
the "ctrl->ctrl.opts = NULL" that only sits on the fail_ctrl: path, so
nvme_fc_ctrl_free() frees the options and nvmf_create_ctrl() frees them
a second time:

  BUG: KASAN: slab-use-after-free in nvmf_free_options+0x30/0x190
   nvmf_free_options+0x30/0x190 drivers/nvme/host/fabrics.c:1284
   nvmf_create_ctrl drivers/nvme/host/fabrics.c:1374 [inline]
  Freed by task 5534:
   nvme_fc_ctrl_free drivers/nvme/host/fc.c:2374 [inline]
   nvme_fc_init_ctrl+0xe17/0x1450 drivers/nvme/host/fc.c:3605

nvme_add_ctrl() fails when dev_set_name() cannot allocate, so this is
reachable under memory pressure or fault injection.  Without KASAN the
options are freed twice.

Rather than clear the pointer on the second exit as well, derive
ownership the way nvme-tcp, nvme-rdma and nvme-loop do, from list
membership: their free_ctrl leaves the options alone unless the
controller made it onto the transport list.

The list cannot simply be populated on the success path as it is there.
nvme-fc runs the initial connect synchronously via flush_delayed_work(),
and the controller has to be reachable on rport->ctrl_list for the whole
of it: nvme_fc_unregister_remoteport() needs to find it to signal
connectivity loss, nvme_fc_match_disconn_ls() matches an incoming
Disconnect Association LS against ctrl->association_id, which is only
assigned during that window, nvme_fc_resume_controller() needs it on
remoteport re-registration, and nvme_fc_existing_controller() uses it to
reject a duplicate connect racing the one in flight.

Keep the insertion where it is and add a fail_unlist: label, falling
into fail_ctrl:, for the error paths that run after it.  The earlier
error paths never reach the insertion and keep using fail_ctrl:
directly, so the list is only touched where the controller is actually
on it.

nvme_fc_ctrl_free() cannot use the plain "goto free_ctrl" the other
transports use, because it still has to put_device(), release the rport
reference and free the ida entry for resources taken before the
insertion.  Sample list_empty() under rport->lock instead.

ctrl->ctrl.opts also stays valid for the whole teardown now.  That is
not the bug being fixed, but it removes some fragility around the old
idiom: nvme_free_ctrl() calls nvme_auth_free() before ->free_ctrl(), and
ctrl_max_dhchaps() dereferences ctrl->opts without a NULL check when
ctrl->dhchap_ctxs is set, which nvme-fc permits since NVMF_ALLOWED_OPTS
allows the dhchap options.  The nvme sysfs attributes that dereference
ctrl->opts, such as hostnqn and address, evaluate their is_visible()
test once at device_add() time and stay readable until
cdev_device_del().

Fixes: 1a9e218195a5 ("nvme: split device add from initialization")
Cc: stable@vger.kernel.org
Reported-by: syzbot+f58e57380a6083c4041d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f58e57380a6083c4041d
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/nvme/host/fc.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index 04363b9c4489..7e1794f054d6 100644
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -2358,9 +2358,15 @@ nvme_fc_ctrl_free(struct kref *ref)
 	struct nvme_fc_ctrl *ctrl =
 		container_of(ref, struct nvme_fc_ctrl, ref);
 	unsigned long flags;
+	bool owns_opts;
 
-	/* remove from rport list */
+	/*
+	 * Presence on the rport list means nvme_fc_init_ctrl() completed,
+	 * and with it ownership of the fabrics options passed to it. If it
+	 * failed instead, the options still belong to nvmf_create_ctrl().
+	 */
 	spin_lock_irqsave(&ctrl->rport->lock, flags);
+	owns_opts = !list_empty(&ctrl->ctrl_list);
 	list_del(&ctrl->ctrl_list);
 	spin_unlock_irqrestore(&ctrl->rport->lock, flags);
 
@@ -2370,7 +2376,7 @@ nvme_fc_ctrl_free(struct kref *ref)
 	nvme_fc_rport_put(ctrl->rport);
 
 	ida_free(&nvme_fc_ctrl_cnt, ctrl->cnum);
-	if (ctrl->ctrl.opts)
+	if (owns_opts)
 		nvmf_free_options(ctrl->ctrl.opts);
 	kfree(ctrl);
 }
@@ -3569,14 +3575,14 @@ nvme_fc_init_ctrl(struct device *dev, struct nvmf_ctrl_options *opts,
 	if (!nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_CONNECTING)) {
 		dev_err(ctrl->ctrl.device,
 			"NVME-FC{%d}: failed to init ctrl state\n", ctrl->cnum);
-		goto fail_ctrl;
+		goto fail_unlist;
 	}
 
 	if (!queue_delayed_work(nvme_wq, &ctrl->connect_work, 0)) {
 		dev_err(ctrl->ctrl.device,
 			"NVME-FC{%d}: failed to schedule initial connect\n",
 			ctrl->cnum);
-		goto fail_ctrl;
+		goto fail_unlist;
 	}
 
 	flush_delayed_work(&ctrl->connect_work);
@@ -3587,14 +3593,22 @@ nvme_fc_init_ctrl(struct device *dev, struct nvmf_ctrl_options *opts,
 
 	return &ctrl->ctrl;
 
+fail_unlist:
+	/*
+	 * Leaving the list hands the options back to nvmf_create_ctrl();
+	 * see nvme_fc_ctrl_free().  Re-init so that list_empty() there
+	 * reports the controller as unlisted.
+	 */
+	spin_lock_irqsave(&rport->lock, flags);
+	list_del_init(&ctrl->ctrl_list);
+	spin_unlock_irqrestore(&rport->lock, flags);
+
 fail_ctrl:
 	nvme_change_ctrl_state(&ctrl->ctrl, NVME_CTRL_DELETING);
 	cancel_work_sync(&ctrl->ioerr_work);
 	cancel_work_sync(&ctrl->ctrl.reset_work);
 	cancel_delayed_work_sync(&ctrl->connect_work);
 
-	ctrl->ctrl.opts = NULL;
-
 	if (ctrl->ctrl.admin_tagset)
 		nvme_remove_admin_tag_set(&ctrl->ctrl);
 	/* initiate nvme ctrl ref counting teardown */
-- 
2.55.0