afs: Fix SELinux setting security label on /afs

Make the AFS dynamic root superblock R/W so that SELinux can set the
security label on it.  Without this, upgrades to, say, the Fedora
filesystem-afs RPM fail if afs is mounted on it because the SELinux label
can't be (re-)applied.

It might be better to make it possible to bypass the R/O check for LSM
label application through setxattr.

Fixes: 4d673da ("afs: Support the AFS dynamic root")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: selinux@vger.kernel.org
cc: linux-security-module@vger.kernel.org

fs/afs/super.c

@@ -448,7 +448,6 @@ static int afs_fill_super(struct super_block *sb, struct afs_fs_context *ctx)
 	/* allocate the root inode and dentry */
 	if (as->dyn_root) {
 		inode = afs_iget_pseudo_dir(sb, true);
-		sb->s_flags	|= SB_RDONLY;
 	} else {
 		sprintf(sb->s_id, "%llu", as->volume->vid);
 		afs_activate_volume(as->volume);