On Tue, May 29, 2018 at 04:43:19PM +0200, Miklos Szeredi wrote:
> Implement stacked mmap.
>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> fs/overlayfs/file.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 7b47dce4b072..4057bbf2e141 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -255,6 +255,33 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
> return ret;
> }
>
> +static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct fd real;
> + const struct cred *old_cred;
> + int ret;
> +
> + ret = ovl_real_fdget(file, &real);
> + if (ret)
> + return ret;
> +
> + /* transfer ref: */
> + fput(vma->vm_file);
> + vma->vm_file = get_file(real.file);
> + fdput(real);
> +
> + if (!vma->vm_file->f_op->mmap)
> + return -ENODEV;
That's broken. ->mmap() failure will fput(file), not fput(vma->vm_file).
What's more, _here_ your "corner case" is a huge DoS - open file r/o,
then have somebody else trigger copyup, then do tons of MAP_PRIVATE
mmaps on the r/o descriptor. *EACH* *OF* *THEM* will open a separate
struct file and stash into into new vmas.
NAK with extreme prejudice, sensu PTerry...
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