[PATCH v3] drm/cma-helper: Fix crash in fbdev error path

Sergey Suloev ssuloev at orpaltech.com
Sun Nov 4 16:14:48 UTC 2018


This doesn't seem to fix the initially reported issue. The problem still 
exists with 4.19.

On 10/2/18 2:14 PM, Noralf Trønnes wrote:
>
> Den 01.10.2018 21.45, skrev Noralf Trønnes:
>> Sergey Suloev reported a crash happening in drm_client_dev_hotplug()
>> when fbdev had failed to register.
>>
>> [    9.124598] vc4_hdmi 3f902000.hdmi: ASoC: Failed to create 
>> component debugfs directory
>> [    9.147667] vc4_hdmi 3f902000.hdmi: vc4-hdmi-hifi <-> 
>> 3f902000.hdmi mapping ok
>> [    9.155184] vc4_hdmi 3f902000.hdmi: ASoC: no DMI vendor name!
>> [    9.166544] vc4-drm soc:gpu: bound 3f902000.hdmi (ops vc4_hdmi_ops 
>> [vc4])
>> [    9.173840] vc4-drm soc:gpu: bound 3f806000.vec (ops vc4_vec_ops 
>> [vc4])
>> [    9.181029] vc4-drm soc:gpu: bound 3f004000.txp (ops vc4_txp_ops 
>> [vc4])
>> [    9.188519] vc4-drm soc:gpu: bound 3f400000.hvs (ops vc4_hvs_ops 
>> [vc4])
>> [    9.195690] vc4-drm soc:gpu: bound 3f206000.pixelvalve (ops 
>> vc4_crtc_ops [vc4])
>> [    9.203523] vc4-drm soc:gpu: bound 3f207000.pixelvalve (ops 
>> vc4_crtc_ops [vc4])
>> [    9.215032] vc4-drm soc:gpu: bound 3f807000.pixelvalve (ops 
>> vc4_crtc_ops [vc4])
>> [    9.274785] vc4-drm soc:gpu: bound 3fc00000.v3d (ops vc4_v3d_ops 
>> [vc4])
>> [    9.290246] [drm] Initialized vc4 0.0.0 20140616 for soc:gpu on 
>> minor 0
>> [    9.297464] [drm] Supports vblank timestamp caching Rev 2 
>> (21.10.2013).
>> [    9.304600] [drm] Driver supports precise vblank timestamp query.
>> [    9.382856] vc4-drm soc:gpu: [drm:drm_fb_helper_fbdev_setup 
>> [drm_kms_helper]] *ERROR* Failed to set fbdev configuration
>> [   10.404937] Unable to handle kernel paging request at virtual 
>> address 00330a656369768a
>> [   10.441620] [00330a656369768a] address between user and kernel 
>> address ranges
>> [   10.449087] Internal error: Oops: 96000004 [#1] PREEMPT SMP
>> [   10.454762] Modules linked in: brcmfmac vc4 drm_kms_helper 
>> cfg80211 drm rfkill smsc95xx brcmutil usbnet 
>> drm_panel_orientation_quirks raspberrypi_hwmon bcm2835_dma crc32_ce 
>> pwm_bcm2835 bcm2835_rng virt_dma rng_core i2c_bcm2835 ip_tables 
>> x_tables ipv6
>> [   10.477296] CPU: 2 PID: 45 Comm: kworker/2:1 Not tainted 
>> 4.19.0-rc5 #3
>> [   10.483934] Hardware name: Raspberry Pi 3 Model B Rev 1.2 (DT)
>> [   10.489966] Workqueue: events output_poll_execute [drm_kms_helper]
>> [   10.596515] Process kworker/2:1 (pid: 45, stack limit = 
>> 0x000000007e8924dc)
>> [   10.603590] Call trace:
>> [   10.606259]  drm_client_dev_hotplug+0x5c/0xb0 [drm]
>> [   10.611303]  drm_kms_helper_hotplug_event+0x30/0x40 [drm_kms_helper]
>> [   10.617849]  output_poll_execute+0xc4/0x1e0 [drm_kms_helper]
>> [   10.623616]  process_one_work+0x1c8/0x318
>> [   10.627695]  worker_thread+0x48/0x428
>> [   10.631420]  kthread+0xf8/0x128
>> [   10.634615]  ret_from_fork+0x10/0x18
>> [   10.638255] Code: 54000220 f9401261 aa1303e0 b4000141 (f9400c21)
>> [   10.644456] ---[ end trace c75b4a4b0e141908 ]---
>>
>> The reason for this is that drm_fbdev_cma_init() removes the drm_client
>> when fbdev registration fails, but it doesn't remove the client from the
>> drm_device client list. So the client list now has a pointer that points
>> into the unknown and we have a 'use after free' situation.
>>
>> Split drm_client_new() into drm_client_init() and drm_client_add() to 
>> fix
>> removal in the error path.
>>
>> Fixes: 894a677f4b3e ("drm/cma-helper: Use the generic fbdev emulation")
>> Reported-by: Sergey Suloev <ssuloev at orpaltech.com>
>> Cc: Stefan Wahren <stefan.wahren at i2se.com>
>> Cc: Eric Anholt <eric at anholt.net>
>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
>> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>> ---
>
> Applied to drm-misc-fixes, thanks for the review.
>
> Noralf.
>
>> Changes since version 2:
>> - Fix drm_client_new() ref in docs (Daniel)
>> - Expand drm_client_add() docs (Daniel)
>>
>> Changes since version 1:
>> - Split drm_client_new() instead of letting drm_client hang around 
>> (Daniel)
>>
>>   drivers/gpu/drm/drm_client.c        | 35 
>> ++++++++++++++++++++++++++---------
>>   drivers/gpu/drm/drm_fb_cma_helper.c |  4 +++-
>>   drivers/gpu/drm/drm_fb_helper.c     |  4 +++-
>>   include/drm/drm_client.h            |  5 +++--
>>   4 files changed, 35 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
>> index 17d9a64e885e..fc03d26fcacc 100644
>> --- a/drivers/gpu/drm/drm_client.c
>> +++ b/drivers/gpu/drm/drm_client.c
>> @@ -63,20 +63,21 @@ static void drm_client_close(struct 
>> drm_client_dev *client)
>>   EXPORT_SYMBOL(drm_client_close);
>>     /**
>> - * drm_client_new - Create a DRM client
>> + * drm_client_init - Initialise a DRM client
>>    * @dev: DRM device
>>    * @client: DRM client
>>    * @name: Client name
>>    * @funcs: DRM client functions (optional)
>>    *
>> + * This initialises the client and opens a &drm_file. Use 
>> drm_client_add() to complete the process.
>>    * The caller needs to hold a reference on @dev before calling this 
>> function.
>>    * The client is freed when the &drm_device is unregistered. See 
>> drm_client_release().
>>    *
>>    * Returns:
>>    * Zero on success or negative error code on failure.
>>    */
>> -int drm_client_new(struct drm_device *dev, struct drm_client_dev 
>> *client,
>> -           const char *name, const struct drm_client_funcs *funcs)
>> +int drm_client_init(struct drm_device *dev, struct drm_client_dev 
>> *client,
>> +            const char *name, const struct drm_client_funcs *funcs)
>>   {
>>       int ret;
>>   @@ -95,10 +96,6 @@ int drm_client_new(struct drm_device *dev, 
>> struct drm_client_dev *client,
>>       if (ret)
>>           goto err_put_module;
>>   -    mutex_lock(&dev->clientlist_mutex);
>> -    list_add(&client->list, &dev->clientlist);
>> -    mutex_unlock(&dev->clientlist_mutex);
>> -
>>       drm_dev_get(dev);
>>         return 0;
>> @@ -109,13 +106,33 @@ int drm_client_new(struct drm_device *dev, 
>> struct drm_client_dev *client,
>>         return ret;
>>   }
>> -EXPORT_SYMBOL(drm_client_new);
>> +EXPORT_SYMBOL(drm_client_init);
>> +
>> +/**
>> + * drm_client_add - Add client to the device list
>> + * @client: DRM client
>> + *
>> + * Add the client to the &drm_device client list to activate its 
>> callbacks.
>> + * @client must be initialized by a call to drm_client_init(). After
>> + * drm_client_add() it is no longer permissible to call 
>> drm_client_release()
>> + * directly (outside the unregister callback), instead cleanup will 
>> happen
>> + * automatically on driver unload.
>> + */
>> +void drm_client_add(struct drm_client_dev *client)
>> +{
>> +    struct drm_device *dev = client->dev;
>> +
>> +    mutex_lock(&dev->clientlist_mutex);
>> +    list_add(&client->list, &dev->clientlist);
>> +    mutex_unlock(&dev->clientlist_mutex);
>> +}
>> +EXPORT_SYMBOL(drm_client_add);
>>     /**
>>    * drm_client_release - Release DRM client resources
>>    * @client: DRM client
>>    *
>> - * Releases resources by closing the &drm_file that was opened by 
>> drm_client_new().
>> + * Releases resources by closing the &drm_file that was opened by 
>> drm_client_init().
>>    * It is called automatically if the &drm_client_funcs.unregister 
>> callback is _not_ set.
>>    *
>>    * This function should only be called from the unregister 
>> callback. An exception
>> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c 
>> b/drivers/gpu/drm/drm_fb_cma_helper.c
>> index 47e0e2f6642d..fb0dfc62b1b6 100644
>> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
>> @@ -167,7 +167,7 @@ struct drm_fbdev_cma *drm_fbdev_cma_init(struct 
>> drm_device *dev,
>>         fb_helper = &fbdev_cma->fb_helper;
>>   -    ret = drm_client_new(dev, &fb_helper->client, "fbdev", NULL);
>> +    ret = drm_client_init(dev, &fb_helper->client, "fbdev", NULL);
>>       if (ret)
>>           goto err_free;
>>   @@ -176,6 +176,8 @@ struct drm_fbdev_cma *drm_fbdev_cma_init(struct 
>> drm_device *dev,
>>       if (ret)
>>           goto err_client_put;
>>   +    drm_client_add(&fb_helper->client);
>> +
>>       return fbdev_cma;
>>     err_client_put:
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c 
>> b/drivers/gpu/drm/drm_fb_helper.c
>> index a504a5e05676..e9095537e0c0 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -3229,13 +3229,15 @@ int drm_fbdev_generic_setup(struct drm_device 
>> *dev, unsigned int preferred_bpp)
>>       if (!fb_helper)
>>           return -ENOMEM;
>>   -    ret = drm_client_new(dev, &fb_helper->client, "fbdev", 
>> &drm_fbdev_client_funcs);
>> +    ret = drm_client_init(dev, &fb_helper->client, "fbdev", 
>> &drm_fbdev_client_funcs);
>>       if (ret) {
>>           kfree(fb_helper);
>>           DRM_DEV_ERROR(dev->dev, "Failed to register client: %d\n", 
>> ret);
>>           return ret;
>>       }
>>   +    drm_client_add(&fb_helper->client);
>> +
>>       fb_helper->preferred_bpp = preferred_bpp;
>>         ret = drm_fbdev_client_hotplug(&fb_helper->client);
>> diff --git a/include/drm/drm_client.h b/include/drm/drm_client.h
>> index 989f8e52864d..971bb7853776 100644
>> --- a/include/drm/drm_client.h
>> +++ b/include/drm/drm_client.h
>> @@ -87,9 +87,10 @@ struct drm_client_dev {
>>       struct drm_file *file;
>>   };
>>   -int drm_client_new(struct drm_device *dev, struct drm_client_dev 
>> *client,
>> -           const char *name, const struct drm_client_funcs *funcs);
>> +int drm_client_init(struct drm_device *dev, struct drm_client_dev 
>> *client,
>> +            const char *name, const struct drm_client_funcs *funcs);
>>   void drm_client_release(struct drm_client_dev *client);
>> +void drm_client_add(struct drm_client_dev *client);
>>     void drm_client_dev_unregister(struct drm_device *dev);
>>   void drm_client_dev_hotplug(struct drm_device *dev);
>


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