nfs: do not export idmapped mounts

Prevent nfs from exporting idmapped mounts until we have ported it to
support exporting idmapped mounts.

Link: https://lore.kernel.org/linux-api/20210123130958.3t6kvgkl634njpsm@wittgenstein
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: "J. Bruce Fields" <bfields@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index 81e7bb1..e456421 100644 (file)
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -369,8 +369,9 @@ static struct svc_export *svc_export_update(struct svc_export *new,
                                            struct svc_export *old);
 static struct svc_export *svc_export_lookup(struct svc_export *);
 
-static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
+static int check_export(struct path *path, int *flags, unsigned char *uuid)
 {
+       struct inode *inode = d_inode(path->dentry);
 
        /*
         * We currently export only dirs, regular files, and (for v4
@@ -394,6 +395,7 @@ static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
         *       or an FSID number (so NFSEXP_FSID or ->uuid is needed).
         * 2:  We must be able to find an inode from a filehandle.
         *       This means that s_export_op must be set.
+        * 3: We must not currently be on an idmapped mount.
         */
        if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) &&
            !(*flags & NFSEXP_FSID) &&
@@ -408,6 +410,11 @@ static int check_export(struct inode *inode, int *flags, unsigned char *uuid)
                return -EINVAL;
        }
 
+       if (mnt_user_ns(path->mnt) != &init_user_ns) {
+               dprintk("exp_export: export of idmapped mounts not yet supported.\n");
+               return -EINVAL;
+       }
+
        if (inode->i_sb->s_export_op->flags & EXPORT_OP_NOSUBTREECHK &&
            !(*flags & NFSEXP_NOSUBTREECHECK)) {
                dprintk("%s: %s does not support subtree checking!\n",
@@ -636,8 +643,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
                                goto out4;
                }
 
-               err = check_export(d_inode(exp.ex_path.dentry), &exp.ex_flags,
-                                  exp.ex_uuid);
+               err = check_export(&exp.ex_path, &exp.ex_flags, exp.ex_uuid);
                if (err)
                        goto out4;
                /*