Commit 1cc36ed5 authored Dec 01, 2021 by Johan Hovold Committed by Greg Kroah-Hartman Jan 20, 2022

firmware: qemu_fw_cfg: fix NULL-pointer deref on duplicate entries

commit d3e305592d69e21e36b76d24ca3c01971a2d09be upstream.

Commit fe3c60684377 ("firmware: Fix a reference count leak.") "fixed"
a kobject leak in the file registration helper by properly calling
kobject_put() for the entry in case registration of the object fails
(e.g. due to a name collision).

This would however result in a NULL pointer dereference when the
release function tries to remove the never added entry from the
fw_cfg_entry_cache list.

Fix this by moving the list-removal out of the release function.

Note that the offending commit was one of the benign looking umn.edu
fixes which was reviewed but not reverted. [1][2]

[1] https://lore.kernel.org/r/202105051005.49BFABCE@keescook
[2] https://lore.kernel.org/all/YIg7ZOZvS3a8LjSv@kroah.com



Fixes: fe3c60684377 ("firmware: Fix a reference count leak.")
Cc: stable@vger.kernel.org      # 5.8
Cc: Qiushi Wu <wu000273@umn.edu>
Cc: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211201132528.30025-2-johan@kernel.org


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b543e414

drivers/firmware/qemu_fw_cfg.c

+1 −4

Original line number	Diff line number	Diff line
		@@ -385,9 +385,7 @@ static void fw_cfg_sysfs_cache_cleanup(void)
		struct fw_cfg_sysfs_entry entry, next;

		list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
		/* will end up invoking fw_cfg_sysfs_cache_delist()
		* via each object's release() method (i.e. destructor)
		*/
		fw_cfg_sysfs_cache_delist(entry);
		kobject_put(&entry->kobj);
		}
		}
		@@ -445,7 +443,6 @@ static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
		{
		struct fw_cfg_sysfs_entry *entry = to_entry(kobj);

		fw_cfg_sysfs_cache_delist(entry);
		kfree(entry);
		}