From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:48672 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752250AbdBMUp0 (ORCPT ); Mon, 13 Feb 2017 15:45:26 -0500 Date: Mon, 13 Feb 2017 15:45:26 -0500 From: Vivek Goyal To: linux-fsdevel Cc: Amir Goldstein , "Eric W. Biederman" , Al Viro , James Bottomley , Miklos Szeredi Subject: [PATCH][V2] vfs: Use upper filesystem inode in bprm_fill_uid() Message-ID: <20170213204526.GG2065@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Right now bprm_fill_uid() uses inode fetched from file_inode(bprm->file). This in turn returns inode of lower filesystem (in a stacked filesystem setup). I was playing with modified patches of shiftfs posted by james bottomley and realized that through shiftfs setuid bit does not take effect. And reason being that we fetch uid/gid from inode of lower fs (and not from shiftfs inode). And that results in following checks failing. /* We ignore suid/sgid if there are no mappings for them in the ns */ if (!kuid_has_mapping(bprm->cred->user_ns, uid) || !kgid_has_mapping(bprm->cred->user_ns, gid)) return; uid/gid fetched from lower fs inode might not be mapped inside the user namespace of container. So we need to look at uid/gid fetched from upper filesystem (shiftfs in this particular case) and these should be mapped and setuid bit can take affect. Signed-off-by: Vivek Goyal --- fs/exec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: rhvgoyal-linux/fs/exec.c =================================================================== --- rhvgoyal-linux.orig/fs/exec.c 2017-02-13 15:22:57.107114781 -0500 +++ rhvgoyal-linux/fs/exec.c 2017-02-13 15:24:19.568114781 -0500 @@ -1479,7 +1479,7 @@ static void bprm_fill_uid(struct linux_b if (task_no_new_privs(current)) return; - inode = file_inode(bprm->file); + inode = bprm->file->f_path.dentry->d_inode; mode = READ_ONCE(inode->i_mode); if (!(mode & (S_ISUID|S_ISGID))) return;