[PATCH 5.17 0554/1126] cxl/port: Hold port reference until decoder release

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 05:10:56 EST

From: Dan Williams <dan.j.williams@xxxxxxxxx>

[ Upstream commit 74be98774dfbc5b8b795db726bd772e735d2edd4 ]

KASAN + DEBUG_KOBJECT_RELEASE reports a potential use-after-free in
cxl_decoder_release() where it goes to reference its parent, a cxl_port,
to free its id back to port->decoder_ida.

BUG: KASAN: use-after-free in to_cxl_port+0x18/0x90 [cxl_core]
Read of size 8 at addr ffff888119270908 by task kworker/35:2/379

CPU: 35 PID: 379 Comm: kworker/35:2 Tainted: G OE 5.17.0-rc2+ #198
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Workqueue: events kobject_delayed_cleanup
Call Trace:
? to_cxl_port+0x18/0x90 [cxl_core]
? to_cxl_port+0x18/0x90 [cxl_core]
to_cxl_port+0x18/0x90 [cxl_core]
cxl_decoder_release+0x2a/0x60 [cxl_core]

The device core only guarantees parent lifetime until all children are
unregistered. If a child needs a parent to complete its ->release()
callback that child needs to hold a reference to extend the lifetime of
the parent.

Fixes: 40ba17afdfab ("cxl/acpi: Introduce cxl_decoder objects")
Reported-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
Tested-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
Reviewed-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
Link: https://lore.kernel.org/r/164505751190.4175768.13324905271463416712.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/cxl/core/port.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 3f9b98ecd18b..aa5239ac67c6 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -182,6 +182,7 @@ static void cxl_decoder_release(struct device *dev)

ida_free(&port->decoder_ida, cxld->id);
+ put_device(&port->dev);

static const struct device_type cxl_decoder_switch_type = {
@@ -500,7 +501,10 @@ struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port, int nr_targets)
if (rc < 0)
goto err;

+ /* need parent to stick around to release the id */
+ get_device(&port->dev);
cxld->id = rc;
cxld->nr_targets = nr_targets;
dev = &cxld->dev;