Messages in this thread | | | Date | Thu, 16 Oct 2008 11:01:27 +0100 | From | Alan Jenkins <> | Subject | Re: [Linux-uvc-devel] [BUG] NULL pointer dereference caused by uvcvideo stress test |
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Laurent Pinchart wrote: > Hi Alan, > > On Wednesday 15 October 2008, Alan Jenkins wrote: > >> Laurent Pinchart wrote: >> >>> On Wednesday 15 October 2008, Alan Jenkins wrote: >>> >>>> If you look at the trace, it happens as "hald-probe-video" opens the >>>> video device. This is from Ubuntu 8.04. Possibly it's significant that >>>> I use the camera first, to make sure it works (I use Kopete, the >>>> settings dialogue includes a video test). >>>> >>> The NULL pointer (or rather 0x00000030 pointer) dereference happens in >>> video_open: >>> >>> file->f_op = fops_get(vfl->fops); >>> if (file->f_op->open) >>> err = file->f_op->open(inode, file); >>> >>> file->f_op ends up being NULL. Either vfl->fops is NULL to begin with, or >>> fops_get failed to get a reference to the file_operations structure. >>> >>> I'd be surprised if vfl->fops was NULL. To rule out that case, can you >>> add a BUG_ON(vfl->fops == NULL) before the call to fops_get ? >>> >>> I'm not too familiar with the module loader, but a quick look at the code >>> shows that the module could be marked as being unloaded >>> (MODULE_STATE_GOING) before its exit function is called. If this is the >>> case video_open would still be called, as the video device would still be >>> registered, but fops_get would fail in try_module_get and return a NULL >>> pointer. It seems the pointer returned by fops_get should be tested in >>> video_open. >>> >>> I've CC'ed the v4l maintainer to get his opinion on this. >>> >> I put one before and one after >> >> 134 BUG_ON(vfl->fops == NULL); >> 135 file->f_op = fops_get(vfl->fops); >> 136 BUG_ON(file->f_op == NULL); >> >> and the second one triggered >> > > This confirms my suspicion. Could you please try the attached patch ? >
Yup, that seems to fix it.
I wonder if there are more instances of this error in other subsystems.
Ta Alan
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