Re: [syzbot] KASAN: use-after-free Read in kernfs_next_descendant_post (2)

[Luis Chamberlain <mcgrof@kernel.org>]

On Mon, Oct 31, 2022 at 12:53:00PM -1000, Tejun Heo wrote:
> (cc'ing Luis for firmware loader and quoting the whole body)
> 
> On Sat, Oct 22, 2022 at 06:52:28AM +0800, Hillf Danton wrote:
> > On 20 Oct 2022 00:15:40 -0700
> > > syzbot has found a reproducer for the following issue on:
> > > 
> > > HEAD commit:    55be6084c8e0 Merge tag 'timers-core-2022-10-05' of git://g..
> > > git tree:       upstream
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1449d53c880000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=df75278aabf0681a
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=6bc35f3913193fe7f0d3
> > > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e01c72880000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1128908c880000
> > 
> > See if the change to ueagle driver alone can survive syzbot test.
> > 
> > #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  aae703b02f92
> > 
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3663,8 +3663,9 @@ static inline bool netif_attr_test_online(unsigned long j,
> >  static inline unsigned int netif_attrmask_next(int n, const unsigned long *srcp,
> >  					       unsigned int nr_bits)
> >  {
> > -	/* n is a prior cpu */
> > -	cpu_max_bits_warn(n + 1, nr_bits);
> > +	/* -1 is a legal arg here. */
> > +	if (n != -1)
> > +		cpu_max_bits_warn(n, nr_bits);
> >  
> >  	if (srcp)
> >  		return find_next_bit(srcp, nr_bits, n + 1);
> > @@ -3685,8 +3686,9 @@ static inline int netif_attrmask_next_and(int n, const unsigned long *src1p,
> >  					  const unsigned long *src2p,
> >  					  unsigned int nr_bits)
> >  {
> > -	/* n is a prior cpu */
> > -	cpu_max_bits_warn(n + 1, nr_bits);
> > +	/* -1 is a legal arg here. */
> > +	if (n != -1)
> > +		cpu_max_bits_warn(n, nr_bits);
> >  
> >  	if (src1p && src2p)
> >  		return find_next_and_bit(src1p, src2p, nr_bits, n + 1);
> > --- a/drivers/usb/atm/ueagle-atm.c
> > +++ b/drivers/usb/atm/ueagle-atm.c
> > @@ -597,9 +597,8 @@ static int uea_send_modem_cmd(struct usb
> >  }
> >  
> >  static void uea_upload_pre_firmware(const struct firmware *fw_entry,
> > -								void *context)
> > +					struct usb_device *usb)
> >  {
> > -	struct usb_device *usb = context;
> >  	const u8 *pfw;
> >  	u8 value;
> >  	u32 crc = 0;
> > @@ -679,6 +678,7 @@ static int uea_load_firmware(struct usb_
> >  {
> >  	int ret;
> >  	char *fw_name = EAGLE_FIRMWARE;
> > +	const struct firmware *fw;
> >  
> >  	uea_enters(usb);
> >  	uea_info(usb, "pre-firmware device, uploading firmware\n");
> > @@ -701,13 +701,13 @@ static int uea_load_firmware(struct usb_
> >  		break;
> >  	}
> >  
> > -	ret = request_firmware_nowait(THIS_MODULE, 1, fw_name, &usb->dev,
> > -					GFP_KERNEL, usb,
> > -					uea_upload_pre_firmware);
> > +	ret = request_firmware(&fw, fw_name, &usb->dev);
> >  	if (ret)
> >  		uea_err(usb, "firmware %s is not available\n", fw_name);
> > -	else
> > +	else {
> >  		uea_info(usb, "loading firmware %s\n", fw_name);
> > +		uea_upload_pre_firmware(fw, usb);
> > +	}
> >  
> >  	uea_leaves(usb);
> >  	return ret;
> 
> So, the problem is that while request_firmware_nowait() inc's the ref on the
> device, if the device gets removed later, having a ref isn't sufficient for
> adding stuff to the device. A relatively easy solution would be putting
> these firmware load work items into its own workqueue and flushing it on
> device removal path. Luis, what do you think?

Since we *can* remove a device after we get a module reference and
since fw_cache_is_setup() tries to use the device before get_device()
(even though this is not the issue reported), I think perhaps the fix
below may be generic and best. It would seem this 2After doing this, I considered simply
removing the try_module_get() but a module which is not respnsible for
creating a device is allowed to request firmware for an arbitrary
device, and so that simplification should not be possible. This would
fix 0cfc1e1e7b534 ("firmware loader: fix device lifetime") since v3.7
but as that commit mentions, there were issues even prior to this get_device()
and so this fix is the proper solution to the reported issue in that
commit. This issue would the date back to f8a4bd3456b98 ("firmware
loader: embed device into firmware_priv structure") since v2.6.36.

Please re-test and let me know if this fixes the issue reported.

diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 7c3590fd97c2..177d5767ad3b 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -1141,18 +1141,20 @@ request_firmware_nowait(
 	const char *name, struct device *device, gfp_t gfp, void *context,
 	void (*cont)(const struct firmware *fw, void *context))
 {
+	int err = -ENOMEM;
 	struct firmware_work *fw_work;
 
+	if (get_device(device))
+		return -ENODEV;
+
 	fw_work = kzalloc(sizeof(struct firmware_work), gfp);
 	if (!fw_work)
-		return -ENOMEM;
+		goto err_out;
 
 	fw_work->module = module;
 	fw_work->name = kstrdup_const(name, gfp);
-	if (!fw_work->name) {
-		kfree(fw_work);
-		return -ENOMEM;
-	}
+	if (!fw_work->name)
+		goto err_out_free_work;
 	fw_work->device = device;
 	fw_work->context = context;
 	fw_work->cont = cont;
@@ -1160,21 +1162,26 @@ request_firmware_nowait(
 		(uevent ? FW_OPT_UEVENT : FW_OPT_USERHELPER);
 
 	if (!uevent && fw_cache_is_setup(device, name)) {
-		kfree_const(fw_work->name);
-		kfree(fw_work);
-		return -EOPNOTSUPP;
+		err = -EOPNOTSUPP;
+		goto err_out_free_name;
 	}
 
 	if (!try_module_get(module)) {
-		kfree_const(fw_work->name);
-		kfree(fw_work);
-		return -EFAULT;
+		err = -EFAULT;
+		goto err_out_free_name;
 	}
 
-	get_device(fw_work->device);
 	INIT_WORK(&fw_work->work, request_firmware_work_func);
 	schedule_work(&fw_work->work);
 	return 0;
+
+err_out_free_name:
+	kfree_const(fw_work->name);
+err_out_free_work:
+	kfree(fw_work);
+err_out:
+	put_device(device);
+	return err;
 }
 EXPORT_SYMBOL(request_firmware_nowait);