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

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, 14 Nov 2022 at 18:34, Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> 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.

Hi Luis,

syzbot is a self-service, you can ask it to test any patches for
reports with reproducers following these instructions:
https://bit.do/syzbot#testing-patches

> 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);
>
>
> --
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