Re: [PATCH 09/19] fs: Refuse uid/gid changes which don't map into s_user_ns

Serge E. Hallyn
2015-12-04T17:27:41Z

On Wed, Dec 02, 2015 at 09:40:09AM -0600, Seth Forshee wrote:
> Add checks to inode_change_ok to verify that uid and gid changes
> will map into the superblock's user namespace. If they do not
> fail with -EOVERFLOW. This cannot be overriden with ATTR_FORCE.
>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

... although i could see root on the host being upset that it can't
assign a uid not valid in the mounter's ns. But it does seem safer.

> ---
> fs/attr.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/fs/attr.c b/fs/attr.c
> index 6530ced19697..55b46e3aa888 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -42,6 +42,17 @@ int inode_change_ok(const struct inode *inode, struct iattr *attr)
> return error;
> }
>
> + /*
> + * Verify that uid/gid changes are valid in the target namespace
> + * of the superblock. This cannot be overriden using ATTR_FORCE.
> + */
> + if (ia_valid & ATTR_UID &&
> + from_kuid(inode->i_sb->s_user_ns, attr->ia_uid) == (uid_t)-1)
> + return -EOVERFLOW;
> + if (ia_valid & ATTR_GID &&
> + from_kgid(inode->i_sb->s_user_ns, attr->ia_gid) == (gid_t)-1)
> + return -EOVERFLOW;
> +
> /* If force is set do it anyway. */
> if (ia_valid & ATTR_FORCE)
> return 0;
> --
> 1.9.1
>
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