linux-kernel - Re: [PATCH v2 01/18] vfs: add miscattr ops

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Message-ID: <CAJfpegvy-bSoorAnPVRUxGjR5s10sJp3qRS0K-O91PcDvLSEPg@mail.gmail.com>
Date:   Wed, 24 Mar 2021 09:45:02 +0100
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 01/18] vfs: add miscattr ops

On Wed, Mar 24, 2021 at 6:03 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Mon, Mar 22, 2021 at 03:48:59PM +0100, Miklos Szeredi wrote:
>
> minor nit: copy_fsxattr_{to,from}_user() might be better.
>
> > +int fsxattr_copy_to_user(const struct miscattr *ma, struct fsxattr __user *ufa)
> > +{
> > +     struct fsxattr fa = {
> > +             .fsx_xflags     = ma->fsx_xflags,
> > +             .fsx_extsize    = ma->fsx_extsize,
> > +             .fsx_nextents   = ma->fsx_nextents,
> > +             .fsx_projid     = ma->fsx_projid,
> > +             .fsx_cowextsize = ma->fsx_cowextsize,
> > +     };
>
> That wants a comment along the lines of "guaranteed to be gap-free",
> since otherwise you'd need memset() to avoid an infoleak.

Isn't structure initialization supposed to zero everything not
explicitly initialized?

>
> > +static int ioctl_getflags(struct file *file, void __user *argp)
> > +{
> > +     struct miscattr ma = { .flags_valid = true }; /* hint only */
> > +     unsigned int flags;
> > +     int err;
> > +
> > +     err = vfs_miscattr_get(file_dentry(file), &ma);
>
> Umm...  Just to clarify - do we plan to have that ever called via
> ovl_real_ioctl()?  IOW, is file_dentry() anything other than a way
> to spell ->f_path.dentry here?

Indeed, file_dentry() only makes sense when called from a layer inside
overlayfs.

The one in io_uring() seems wrong also, as a beast needing
file_dentry() should never get out of overlayfs and into io_uring:

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9297,7 +9297,7 @@ static void __io_uring_show_fdinfo(struct
io_ring_ctx *ctx, struct seq_file *m)
                struct file *f = *io_fixed_file_slot(ctx->file_data, i);

                if (f)
-                       seq_printf(m, "%5u: %s\n", i, file_dentry(f)->d_iname);
+                       seq_printf(m, "%5u: %pD\n", i, f);
                else
                        seq_printf(m, "%5u: <none>\n", i);
        }


Thanks,
Miklos