Messages in this thread | | | Date | Mon, 10 Aug 2020 10:11:50 -0700 (PDT) | From | Zwane Mwaikambo <> | Subject | Re: [PATCH] drm: assure aux_dev is nonzero before using it |
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Hi Folks, I know this thread eventually dropped off due to not identifying the underlying issue. It's still occuring on 5.8 and in my case it happened because the udev device nodes for the DP aux devices were not cleaned up whereas the kernel had no association with them. I can reproduce the bug just by creating a device node for a non-existent minor device and calling open().
To me it still makes sense to just check aux_dev because the chardev has no way to check before calling.
(gdb) list *drm_dp_aux_dev_get_by_minor+0x29 0x17b39 is in drm_dp_aux_dev_get_by_minor (drivers/gpu/drm/drm_dp_aux_dev.c:65). 60 static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index) 61 { 62 struct drm_dp_aux_dev *aux_dev = NULL; 63 64 mutex_lock(&aux_idr_mutex); 65 aux_dev = idr_find(&aux_idr, index); 66 if (!kref_get_unless_zero(&aux_dev->refcount)) 67 aux_dev = NULL; 68 mutex_unlock(&aux_idr_mutex); 69 (gdb) p/x &((struct drm_dp_aux_dev *)(0x0))->refcount $8 = 0x18
static int auxdev_open(struct inode *inode, struct file *file) { unsigned int minor = iminor(inode); struct drm_dp_aux_dev *aux_dev;
aux_dev = drm_dp_aux_dev_get_by_minor(minor); if (!aux_dev) return -ENODEV;
file->private_data = aux_dev; return 0; }
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