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    SubjectRe: [Linux-uvc-devel] [BUG] NULL pointer dereference caused by uvcvideo stress test
    Date
    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 ?

    Best regards,

    Laurent Pinchart
    diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c
    index 155fdec..7a3c1ed 100644
    --- a/drivers/media/video/v4l2-dev.c
    +++ b/drivers/media/video/v4l2-dev.c
    @@ -132,6 +132,11 @@ static int video_open(struct inode *inode, struct file *file)
    }
    old_fops = file->f_op;
    file->f_op = fops_get(vfl->fops);
    + if (file->f_op == NULL) {
    + file->f_op = old_fops;
    + err = -ENODEV;
    + goto out;
    + }
    if (file->f_op->open)
    err = file->f_op->open(inode, file);
    if (err) {
    @@ -139,6 +144,7 @@ static int video_open(struct inode *inode, struct file *file)
    file->f_op = fops_get(old_fops);
    }
    fops_put(old_fops);
    +out:
    mutex_unlock(&videodev_lock);
    unlock_kernel();
    return err;
    \
     
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      Last update: 2008-10-15 23:21    [W:0.023 / U:0.208 seconds]
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