From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Date: Mon, 30 Nov 2020 07:48:29 +0000 Subject: Re: [PATCH v2] drm/kmb: Fix possible oops in probe error handling Message-Id: <20201130074829.GA2767@kadam> List-Id: References: <20201117072103.GA1111239@mwanda> <20201120081113.GL18329@kadam> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Chrisanthus, Anitha" Cc: David Airlie , "Dea, Edmund J" , "kernel-janitors@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Sam Ravnborg On Fri, Nov 20, 2020 at 10:15:57PM +0000, Chrisanthus, Anitha wrote: > Hi Dan, > I see the problem now, thanks for the patch. > > > -----Original Message----- > > From: Dan Carpenter > > Sent: Friday, November 20, 2020 12:11 AM > > To: Chrisanthus, Anitha > > Cc: Dea, Edmund J ; David Airlie ; > > Daniel Vetter ; Sam Ravnborg ; dri- > > devel@lists.freedesktop.org; kernel-janitors@vger.kernel.org > > Subject: [PATCH v2] drm/kmb: Fix possible oops in probe error handling > > > > If kmb_dsi_init() fails the "kmb->kmb_dsi" variable is an error pointer. > > The kernel will Oops when we pass it to kmb_dsi_host_unregister(). > > > > Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display") > > Signed-off-by: Dan Carpenter > > --- > > v2: write a better commit message > > > > drivers/gpu/drm/kmb/kmb_drv.c | 5 +++-- > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/kmb/kmb_drv.c > > b/drivers/gpu/drm/kmb/kmb_drv.c > > index a31a840ce634..8c43b136765c 100644 > > --- a/drivers/gpu/drm/kmb/kmb_drv.c > > +++ b/drivers/gpu/drm/kmb/kmb_drv.c > > @@ -504,7 +504,7 @@ static int kmb_probe(struct platform_device *pdev) > > if (IS_ERR(kmb->kmb_dsi)) { > > drm_err(&kmb->drm, "failed to initialize DSI\n"); > > ret = PTR_ERR(kmb->kmb_dsi); > > - goto err_free1; > > + goto err_clear_drvdata; > > } > > > > kmb->kmb_dsi->dev = &dsi_pdev->dev; > > @@ -540,8 +540,9 @@ static int kmb_probe(struct platform_device *pdev) > > drm_crtc_cleanup(&kmb->crtc); > > drm_mode_config_cleanup(&kmb->drm); > > err_free1: > > - dev_set_drvdata(dev, NULL); > > kmb_dsi_host_unregister(kmb->kmb_dsi); > > + err_clear_drvdata: > We still need to unregister the dsi_host that was registered in this call kmb_dsi_host_bridge_init. > This will require more changes in kmb_dsi_host_unregister and/or separate out mipi_dsi_host_unregister. > FYI - I will be out all of next week, will be back the next Monday. Hm... Yes. Now that you point it out, there are several bugs related to kmb_dsi_host_bridge_init()... 182 void kmb_dsi_host_unregister(struct kmb_dsi *kmb_dsi) 183 { 184 kmb_dsi_clk_disable(kmb_dsi); 185 mipi_dsi_host_unregister(kmb_dsi->host); ^^^^^^^^^^^^^ kmb_dsi->host is dsi_host. Every user unregisters it, but only the first user registers it. So if there are multiple users it will be unregistered prematurely. Should there be a kfree to prevent a leak? kfree(kmb_dsi->host); dsi_host = NULL; 186 } [ snip ] 216 int kmb_dsi_host_bridge_init(struct device *dev) 217 { 218 struct device_node *encoder_node, *dsi_out; 219 220 /* Create and register MIPI DSI host */ 221 if (!dsi_host) { ^^^^^^^^ This is only allocated for the first user. 222 dsi_host = kzalloc(sizeof(*dsi_host), GFP_KERNEL); 223 if (!dsi_host) 224 return -ENOMEM; 225 226 dsi_host->ops = &kmb_dsi_host_ops; 227 228 if (!dsi_device) { 229 dsi_device = kzalloc(sizeof(*dsi_device), GFP_KERNEL); 230 if (!dsi_device) { 231 kfree(dsi_host); ^^^^^^^^^^^^^^^ But now it is non-NULL but it is a freed pointer. dsi_host = NULL; 232 return -ENOMEM; 233 } 234 } 235 236 dsi_host->dev = dev; 237 mipi_dsi_host_register(dsi_host); 238 } 239 [ snip ] 482 483 of_node_put(dsi_in); 484 of_node_put(dsi_node); 485 ret = kmb_dsi_host_bridge_init(get_device(&dsi_pdev->dev)); ^^^^^^^^^^^^^^^^^^^^^^^^^^ This get_device() needs a matching put_device(). I kind of like to put the kref_get() calls on their own line so that they're more obvious to the reader. get_device(&dsi_pdev->dev); kmb_dsi_host_bridge_init(&dsi_pdev->dev); 486 487 if (ret = -EPROBE_DEFER) { 488 return -EPROBE_DEFER; 489 } else if (ret) { 490 DRM_ERROR("probe failed to initialize DSI host bridge\n"); 491 return ret; 492 } 493 494 /* Create DRM device */ 495 kmb = devm_drm_dev_alloc(dev, &kmb_driver, 496 struct kmb_drm_private, drm); 497 if (IS_ERR(kmb)) 498 return PTR_ERR(kmb); On these error paths we would want to unwind using a call to kmb_dsi_host_unregister(). 499 500 dev_set_drvdata(dev, &kmb->drm); 501 502 /* Initialize MIPI DSI */ 503 kmb->kmb_dsi = kmb_dsi_init(dsi_pdev); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This is the call where the "kmb_dsi->host = dsi_host;" assignment actually happens. 504 if (IS_ERR(kmb->kmb_dsi)) { 505 drm_err(&kmb->drm, "failed to initialize DSI\n"); 506 ret = PTR_ERR(kmb->kmb_dsi); 507 goto err_free1; 508 } 509 510 kmb->kmb_dsi->dev = &dsi_pdev->dev; 511 kmb->kmb_dsi->pdev = dsi_pdev; 512 ret = kmb_hw_init(&kmb->drm, 0); It feels like it would be a lot easier if the kmb_dsi_init() and kmb_dsi_host_bridge_init() functions were combined. Probably the dsi_host and dsi_device stuff needs to be refcounted? Anyway, I can't test this stuff and I'm not really familiar with the driver. Could you fix it and CC me on the fix? regards, dan carpenter