Re: [PATCH RFC] [media] v4l: async: don't bomb out on ->complete failure

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Fri, 29 Sep 2017 22:33:36 +0100
Russell King <rmk+kernel@armlinux.org.uk> escreveu:

> When a subdev is being registered via v4l2_async_register_subdev(), we
> test to see if we have all the components, and if so, we call the
> ->complete() handler.  
> 
> However, the error handling is broken - if notifier->complete() returns
> an error, we propagate the error out of v4l2_async_register_subdev(),
> but leaving the subdev bound and on the notifier's "done" list.
> 
> Drivers calling v4l2_async_register_subdev() assume that this means
> that v4l2_async_register_subdev() failed, which causes probe failure
> and the memory backing the subdev to be freed.
> 
> At this point, we now have a subdev on the notifier's done list which
> has been freed.  If we then try to remove the notifier via
> v4l2_async_notifier_unregister(), we walk the notifier's done list,
> cleaning up the subdevs - and hit the freed subdev, causing a kernel
> oops such as:
> 
> Unable to handle kernel paging request at virtual address 6e6f6994
> pgd = d039c000
> [6e6f6994] *pgd=00000000
> Internal error: Oops: 5 [#1] SMP ARM
> Modules linked in: mux_mmio caam_jr snd_soc_imx_sgtl5000 snd_soc_fsl_asoc_card
>  snd_soc_imx_spdif imx_media_csi(C) ci_hdrc_imx snd_soc_imx_audmux
>  imx6_mipi_csi2(C) imx219 snd_soc_sgtl5000 ci_hdrc usbmisc_imx udc_core
>  caam video_mux mux_core imx_media_ic(C) imx_sdma imx_media_vdic(C)
>  imx_media_capture(C) imx2_wdt snd_soc_fsl_ssi snd_soc_fsl_spdif
>  imx_pcm_dma coda v4l2_mem2mem videobuf2_v4l2 imx_vdoa videobuf2_dma_contig
>  videobuf2_core imx_thermal videobuf2_vmalloc videobuf2_memops imx_media(C-)
>  imx_media_common(C) v4l2_fwnode nfsd rc_pinnacle_pctv_hd dw_hdmi_ahb_audio
>  dw_hdmi_cec etnaviv
> CPU: 1 PID: 8039 Comm: rmmod Tainted: G         C      4.14.0-rc1+ #2194
> Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> task: ee522700 task.stack: e5f68000
> PC is at __lock_acquire+0x98/0x13f4
> LR is at lock_acquire+0xd8/0x250
> pc : [<c008cb00>]    lr : [<c008e828>]    psr: 200e0093
> sp : e5f69d28  ip : e5f68000  fp : e5f69da4
> r10: 00000000  r9 : 00000000  r8 : 6e6f6994
> r7 : 00000000  r6 : c0aa4f64  r5 : ee522700  r4 : c13f4abc
> r3 : 00000000  r2 : 00000001  r1 : 00000000  r0 : 6e6f6994
> Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
> Control: 10c5387d  Table: 2039c04a  DAC: 00000051
> Process rmmod (pid: 8039, stack limit = 0xe5f68210)
> Backtrace:
> [<c008ca68>] (__lock_acquire) from [<c008e828>] (lock_acquire+0xd8/0x250)
> [<c008e750>] (lock_acquire) from [<c0749734>] (_raw_spin_lock+0x34/0x44)
> [<c0749700>] (_raw_spin_lock) from [<c05155b4>] (v4l2_device_unregister_subdev+0x2c/0xb0)
> [<c0515588>] (v4l2_device_unregister_subdev) from [<c051f4d0>] (v4l2_async_cleanup+0x14/0x40)
> [<c051f4bc>] (v4l2_async_cleanup) from [<c051f6dc>] (v4l2_async_notifier_unregister+0xa8/0x1ec)
> [<c051f634>] (v4l2_async_notifier_unregister) from [<bf05802c>] (imx_media_remove+0x2c/0x54 [imx_media])
> [<bf058000>] (imx_media_remove [imx_media]) from [<c043d3a8>] (platform_drv_remove+0x2c/0x44)
> [<c043d37c>] (platform_drv_remove) from [<c043b8d8>] (device_release_driver_internal+0x158/0x1f8)
> [<c043b780>] (device_release_driver_internal) from [<c043b9d4>] (driver_detach+0x40/0x74)
> [<c043b994>] (driver_detach) from [<c043aadc>] (bus_remove_driver+0x54/0x98)
> [<c043aa88>] (bus_remove_driver) from [<c043c5c8>] (driver_unregister+0x30/0x50)
> [<c043c598>] (driver_unregister) from [<c043d274>] (platform_driver_unregister+0x14/0x18)
> [<c043d260>] (platform_driver_unregister) from [<bf059508>] (imx_media_pdrv_exit+0x14/0x1c [imx_media])
> [<bf0594f4>] (imx_media_pdrv_exit [imx_media]) from [<c00d9218>] (SyS_delete_module+0x170/0x1c0)
> [<c00d90a8>] (SyS_delete_module) from [<c00103c0>] (ret_fast_syscall+0x0/0x1c)
> Code: 1a00000e e3a00000 e24bd028 e89daff0 (e5980000)
> ---[ end trace 97732329ac63e5ae ]---
> 
> Avoid this by reporting an error to the kernel message log about the
> failure, rather than silently propagating the error from ->complete()
> and causing this latent use-after-free oops.

Thanks for tracking this issue!

> 
> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> ---
>  drivers/media/v4l2-core/v4l2-async.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> index d741a8e0fdac..8d221f4a8a8d 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -122,8 +122,12 @@ static int v4l2_async_test_notify(struct v4l2_async_notifier *notifier,
>  	/* Move from the global subdevice list to notifier's done */
>  	list_move(&sd->async_list, &notifier->done);
>  
> -	if (list_empty(&notifier->waiting) && notifier->complete)
> -		return notifier->complete(notifier);
> +	if (list_empty(&notifier->waiting) && notifier->complete) {
> +		int ret = notifier->complete(notifier);
> +		if (ret)
> +			dev_err(notifier->v4l2_dev->dev,
> +				"complete notifier failed: %d\n", ret);

Printing the error here is OK...

Yet, v4l2_async_test_notify() should be cleaning up the house and
return the error, instead of returning 0, e. g. something like
(untested):

	if (list_empty(&notifier->waiting) && notifier->complete) {
		int ret = notifier->complete(notifier);
		if (ret) {
			dev_err(notifier->v4l2_dev->dev,
				"complete notifier failed: %d\n", ret);
			v4l2_async_cleanup(sd);
			return (ret);
		}
	}


Thanks,
Mauro