linux-kernel - Re: [PATCH 09/16] fs: add vfs_set

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Date:   Thu, 30 Nov 2023 10:01:55 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     "Seth Forshee (DigitalOcean)" <sforshee@...nel.org>
Cc:     Christian Brauner <brauner@...nel.org>,
        Serge Hallyn <serge@...lyn.com>,
        Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...hat.com>,
        James Morris <jmorris@...ei.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, audit@...r.kernel.org,
        linux-unionfs@...r.kernel.org
Subject: Re: [PATCH 09/16] fs: add vfs_set_fscaps()

On Wed, Nov 29, 2023 at 11:50 PM Seth Forshee (DigitalOcean)
<sforshee@...nel.org> wrote:
>
> Provide a type-safe interface for setting filesystem capabilities and a
> generic implementation suitable for most filesystems.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@...nel.org>
> ---
>  fs/xattr.c         | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  2 ++
>  2 files changed, 89 insertions(+)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 3abaf9bef0a5..03cc824e4f87 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -247,6 +247,93 @@ int vfs_get_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
>  }
>  EXPORT_SYMBOL(vfs_get_fscaps);
>
> +static int generic_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> +                             const struct vfs_caps *caps, int flags)
> +{
> +       struct inode *inode = d_inode(dentry);
> +       struct vfs_ns_cap_data nscaps;
> +       int size;
> +
> +       size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps,
> +                                &nscaps, sizeof(nscaps));
> +       if (size < 0)
> +               return size;
> +
> +       return __vfs_setxattr_noperm(idmap, dentry, XATTR_NAME_CAPS,
> +                                    &nscaps, size, flags);
> +}
> +
> +/**
> + * vfs_set_fscaps - set filesystem capabilities
> + * @idmap: idmap of the mount the inode was found from
> + * @dentry: the dentry on which to set filesystem capabilities
> + * @caps: the filesystem capabilities to be written
> + * @flags: setxattr flags to use when writing the capabilities xattr
> + *
> + * This function writes the supplied filesystem capabilities to the dentry.
> + *
> + * Return: 0 on success, a negative errno on error.
> + */
> +int vfs_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> +                  const struct vfs_caps *caps, int flags)
> +{
> +       struct inode *inode = d_inode(dentry);
> +       struct inode *delegated_inode = NULL;
> +       struct vfs_ns_cap_data nscaps;
> +       int size, error;
> +
> +       /*
> +        * Unfortunately EVM wants to have the raw xattr value to compare to
> +        * the on-disk version, so we need to pass the raw xattr to the
> +        * security hooks. But we also want to do security checks before
> +        * breaking leases, so that means a conversion to the raw xattr here
> +        * which will usually be reduntant with the conversion we do for
> +        * writing the xattr to disk.
> +        */
> +       size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps, &nscaps,
> +                                sizeof(nscaps));
> +       if (size < 0)
> +               return size;
> +
> +retry_deleg:
> +       inode_lock(inode);
> +
> +       error = xattr_permission(idmap, inode, XATTR_NAME_CAPS, MAY_WRITE);
> +       if (error)
> +               goto out_inode_unlock;
> +       error = security_inode_setxattr(idmap, dentry, XATTR_NAME_CAPS, &nscaps,
> +                                       size, flags);
> +       if (error)
> +               goto out_inode_unlock;
> +
> +       error = try_break_deleg(inode, &delegated_inode);
> +       if (error)
> +               goto out_inode_unlock;
> +
> +       if (inode->i_opflags & IOP_XATTR) {
> +               if (inode->i_op->set_fscaps)
> +                       error = inode->i_op->set_fscaps(idmap, dentry, caps, flags);
> +               else
> +                       error = generic_set_fscaps(idmap, dentry, caps, flags);

I think the non-generic case is missing fsnotify_xattr().

See vfs_set_acl() for comparison.

Thanks,
Amir.