On Mon, Oct 01, 2018 at 04:57:32PM +0200, Noralf Trønnes wrote:
> 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@xxxxxxxxxxxxx>
> Cc: Stefan Wahren <stefan.wahren@xxxxxxxx>
> Cc: Eric Anholt <eric@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
>
> Changes since version 1:
> - Split drm_client_new() instead of letting drm_client hang around (Daniel)
>
>
> Just to make sure I don't break anything, would this procedure do the right thing:
>
> dim update-branches
> dim checkout drm-misc-fixes
I recommend a
dim create-worktree drm-misc-fixes
here so that you have a separate checkout. Avoids accidentally thrashin
stuff when switching between branches.
> curl -sS https://patchwork.freedesktop.org/patch/$1/mbox/ > /tmp/patch
> cat /tmp/patch | dim apply-branch drm-misc-fixes
>
> <build test>
>
> dim push-branch drm-misc-fixes
Yup. On the patch, with the nits below addressed:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
>
> drivers/gpu/drm/drm_client.c | 29 +++++++++++++++++++++--------
> 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, 30 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
> index 17d9a64e885e..b466e08931fa 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;
> @@ -109,7 +106,23 @@ 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.
I think this needs a few more details clarified in the doc:
"@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, 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
Grep says you missed one occurrence of drm_client_new() later on in one of
the kerneldoc comments.
> 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);
Shouldn't we move this to later on, with an explicit drm_client_release()
cleanup path, just for safety? Otoh, this is the minimal change, so maybe
in a follow-up patch?
Cheers, Daniel
> +
> 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);
> --
> 2.15.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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