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    SubjectRe: [PATCH] Reset file->f_op in snd_card_file_remove(). Take 2
    Date
    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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