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SubjectRe: [PATCH] Reset file->f_op in snd_card_file_remove(). Take 2
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Am Mittwoch, 4. Oktober 2006 16:18 schrieb Takashi Iwai:
> At Wed, 4 Oct 2006 12:47:19 +0200,
> Karsten Wiese wrote:
> >
> > Am Mittwoch, 4. Oktober 2006 11:22 schrieb Takashi Iwai:
> > >
> > > It should call snd_card_free_when_closed() instead.
> > >
> > IMHO, that would just make sure that the bug happens.
> > Please see my annotations, starting with // in:
> >
> > void fastcall __fput(struct file *file)
> > {
> > struct dentry *dentry = file->f_dentry;
> > struct vfsmount *mnt = file->f_vfsmnt;
> > struct inode *inode = dentry->d_inode;
> >
> > might_sleep();
> >
> > fsnotify_close(file);
> > /*
> > * The function eventpoll_release() should be the first called
> > * in the file cleanup chain.
> > */
> > eventpoll_release(file);
> > locks_remove_flock(file);
> >
> > if (file->f_op && file->f_op->release)
> > file->f_op->release(inode, file);
> > // Here snd_hwdep_release() is called.
> > // snd_hwdep_release() calls snd_card_file_remove().
> > // snd_card_file_remove() sees card->free_on_last_close ist set,
> > // calls snd_card_do_free().
> > // snd_card_do_free frees file->f_op but doesn't set it NULL.
> > //
> > security_file_free(file);
> > if (unlikely(inode->i_cdev != NULL))
> > cdev_put(inode->i_cdev);
> > fops_put(file->f_op);
> > // file->f_op has already been freeed!
> > // fops_put(file->f_op) is likely to oops.
>
> Yes, this looks like an invalid access.
>
> The problem is that we use kmalloc for allocating a dummy f_op.
> IMO, the simlest solution is to use a static dummy f_op.
>
That'd take 1 static dummy f_op per snd_*_release().
I prefer the patch at the start of this thread :-)

Karsten
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