This is a note to let you know that I've just added the patch titled
cxl/port: Hold port reference until decoder release
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cxl-port-hold-port-reference-until-decoder-release.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1ebc4a4f17a863ed464c14b72a5d167428638081
Author: Dan Williams <dan.j.williams@xxxxxxxxx>
Date: Wed Feb 16 16:25:11 2022 -0800
cxl/port: Hold port reference until decoder release
[ 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:
<TASK>
dump_stack_lvl+0x59/0x73
print_address_description.constprop.0+0x1f/0x150
? to_cxl_port+0x18/0x90 [cxl_core]
kasan_report.cold+0x83/0xdf
? to_cxl_port+0x18/0x90 [cxl_core]
to_cxl_port+0x18/0x90 [cxl_core]
cxl_decoder_release+0x2a/0x60 [cxl_core]
device_release+0x5f/0x100
kobject_cleanup+0x80/0x1c0
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>
diff --git a/drivers/cxl/core/bus.c b/drivers/cxl/core/bus.c
index 267d8042bec2..0987a6423ee0 100644
--- a/drivers/cxl/core/bus.c
+++ b/drivers/cxl/core/bus.c
@@ -182,6 +182,7 @@ static void cxl_decoder_release(struct device *dev)
ida_free(&port->decoder_ida, cxld->id);
kfree(cxld);
+ put_device(&port->dev);
}
static const struct device_type cxl_decoder_switch_type = {
@@ -481,6 +482,9 @@ cxl_decoder_alloc(struct cxl_port *port, int nr_targets, resource_size_t base,
if (rc < 0)
goto err;
+ /* need parent to stick around to release the id */
+ get_device(&port->dev);
+
*cxld = (struct cxl_decoder) {
.id = rc,
.range = {
