[ndctl PATCH 07/10] cxl/memdev: Fix bus_invalidate() crash

From: Dan Williams <dan.j.williams@intel.com>
To: vishal.l.verma@intel.com
Cc: linux-cxl@vger.kernel.org, nvdimm@lists.linux.dev
Subject: [ndctl PATCH 07/10] cxl/memdev: Fix bus_invalidate() crash
Date: Thu, 28 Apr 2022 15:10:37 -0700	[thread overview]
Message-ID: <165118383756.1676208.5717187278816036969.stgit@dwillia2-desk3.amr.corp.intel.com> (raw)
In-Reply-To: <165118380037.1676208.7644295506592461996.stgit@dwillia2-desk3.amr.corp.intel.com>

bus_invalidate() attempts to limit the invalidation of memdevs to a single
bus scope. However, the ordering of bus_invalidate() leads to a use after
free. Unconditionally invalidate memdevs (disconnect memdevs from their
endpoints) and resotre on next lookup. Otherwise the following command
results in the following backtrace with cxl_test:

    cxl disable-memdev 5,1 --force

#2  0x00007ffff7fb97d4 in snprintf (__fmt=0x7ffff7fbc3ed "%s/driver", __n=98,
    __s=0x574d545619f7bae2 <error: Cannot access memory at address 0x574d545619f7bae2>)
    at /usr/include/bits/stdio2.h:71
#3  cxl_port_is_enabled (port=port@entry=0x422eb0) at ../cxl/lib/libcxl.c:1379
#4  0x00007ffff7fb99a9 in cxl_port_get_bus (port=0x422eb0) at ../cxl/lib/libcxl.c:1339
#5  0x00007ffff7fba3d0 in bus_invalidate (bus=bus@entry=0x421740) at ../cxl/lib/libcxl.c:549
#6  0x00007ffff7fba4e7 in cxl_memdev_disable_invalidate (memdev=0x416fd0) at ../cxl/lib/libcxl.c:596
#7  0x000000000040624e in memdev_action (argc=<optimized out>, argv=<optimized out>, ctx=0x4152a0,
    action=action@entry=0x406b70 <action_disable>, options=options@entry=0x40fca0 <disable_options>,
    usage=usage@entry=0x40f4b0 "cxl disable-memdev <mem0> [<mem1>..<memN>] [<options>]")
    at ../cxl/memdev.c:506
#8  0x0000000000406d57 in cmd_disable_memdev (argc=<optimized out>, argv=<optimized out>,

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 cxl/lib/libcxl.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/cxl/lib/libcxl.c b/cxl/lib/libcxl.c
index 0e8dd20e3c47..374b0f13905a 100644
--- a/cxl/lib/libcxl.c
+++ b/cxl/lib/libcxl.c
@@ -546,8 +546,7 @@ static void bus_invalidate(struct cxl_bus *bus)
 	 * indeterminate, delete them all and start over.
 	 */
 	cxl_memdev_foreach(ctx, memdev)
-		if (cxl_memdev_get_bus(memdev) == bus)
-			memdev->endpoint = NULL;
+		memdev->endpoint = NULL;
 
 	bus_port = cxl_bus_get_port(bus);
 	list_for_each_safe(&bus_port->child_ports, port, _p, list)

