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From: Jing Xia <jing.xia@unisoc.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki"
	<rafael@kernel.org>
CC: <linux-kernel@vger.kernel.org>, <jing.xia.mail@gmail.com>,
        <xuewen.yan@unisoc.com>, <ke.wang@unisoc.com>,
        <chunyan.zhang@unisoc.com>
Subject: [PATCH V2] class: fix use-after-free in class_register()
Date: Wed, 20 Dec 2023 10:46:03 +0800
Message-ID: <20231220024603.186078-1-jing.xia@unisoc.com>
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The lock_class_key is still registered and can be found in
lock_keys_hash hlist after subsys_private is freed in error
handler path.A task who iterate over the lock_keys_hash
later may cause use-after-free.So fix that up and unregister
the lock_class_key before kfree(cp).

On our platform, a driver fails to kset_register because of
creating duplicate filename '/class/xxx'.With Kasan enabled,
it prints a invalid-access bug report.

KASAN bug report:

BUG: KASAN: invalid-access in lockdep_register_key+0x19c/0x1bc
Write of size 8 at addr 15ffff808b8c0368 by task modprobe/252
Pointer tag: [15], memory tag: [fe]

CPU: 7 PID: 252 Comm: modprobe Tainted: G        W
 6.6.0-mainline-maybe-dirty #1

Call trace:
dump_backtrace+0x1b0/0x1e4
show_stack+0x2c/0x40
dump_stack_lvl+0xac/0xe0
print_report+0x18c/0x4d8
kasan_report+0xe8/0x148
__hwasan_store8_noabort+0x88/0x98
lockdep_register_key+0x19c/0x1bc
class_register+0x94/0x1ec
init_module+0xbc/0xf48 [rfkill]
do_one_initcall+0x17c/0x72c
do_init_module+0x19c/0x3f8
...
Memory state around the buggy address:
ffffff808b8c0100: 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a 8a
ffffff808b8c0200: 8a 8a 8a 8a 8a 8a 8a 8a fe fe fe fe fe fe fe fe
>ffffff808b8c0300: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
                                     ^
ffffff808b8c0400: 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03 03

As CONFIG_KASAN_GENERIC is not set, Kasan reports invalid-access
not use-after-free here.In this case, modprobe is manipulating
the corrupted lock_keys_hash hlish where lock_class_key is already
freed before.

It's worth noting that this only can happen if lockdep is enabled,
which is not true for normal system.

Fixes: dcfbb67e48a2 ("driver core: class: use lock_class_key already present in struct subsys_private")
Signed-off-by: Jing Xia <jing.xia@unisoc.com>
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
---
 drivers/base/class.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index 7e78aee0fd6c..7b38fdf8e1d7 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -213,6 +213,7 @@ int class_register(const struct class *cls)
 	return 0;
 
 err_out:
+	lockdep_unregister_key(key);
 	kfree(cp);
 	return error;
 }
-- 
2.25.1