linux-kernel - Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in driver_remove

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Message-ID: <20250921123825.7352-1-hdanton@sina.com>
Date: Sun, 21 Sep 2025 20:38:24 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+a56aa983ce6a1bf12485@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in driver_remove_file

> Date: Sat, 20 Sep 2025 21:04:28 -0700
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    3b08f56fbbb9 Merge tag 'x86-urgent-2025-09-20' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14ce5858580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8f01d8629880e620
> dashboard link: https://syzkaller.appspot.com/bug?extid=a56aa983ce6a1bf12485
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15571534580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=152f7e42580000

#syz test

--- x/drivers/comedi/drivers.c
+++ y/drivers/comedi/drivers.c
@@ -961,7 +961,7 @@ EXPORT_SYMBOL_GPL(comedi_legacy_detach);
 int comedi_device_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	struct comedi_driver *driv;
-	int ret;
+	int ret, detach;
 
 	lockdep_assert_held(&dev->mutex);
 	if (dev->attached)
@@ -1004,11 +1004,15 @@ int comedi_device_attach(struct comedi_d
 	dev->driver = driv;
 	dev->board_name = dev->board_ptr ? *(const char **)dev->board_ptr
 					 : dev->driver->driver_name;
+	detach = 0;
 	ret = driv->attach(dev, it);
-	if (ret >= 0)
+	if (ret >= 0) {
+		detach = 1;
 		ret = comedi_device_postconfig(dev);
+	}
 	if (ret < 0) {
-		comedi_device_detach(dev);
+		if (detach)
+			comedi_device_detach(dev);
 		module_put(driv->module);
 	}
 	/* On success, the driver module count has been incremented. */
--