From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:48122 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388375AbeGPIKL (ORCPT ); Mon, 16 Jul 2018 04:10:11 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , Andy Lutomirski , Al Viro , Linus Torvalds Subject: [PATCH 4.4 13/43] Fix up non-directory creation in SGID directories Date: Mon, 16 Jul 2018 09:36:18 +0200 Message-Id: <20180716073513.229883114@linuxfoundation.org> In-Reply-To: <20180716073511.796555857@linuxfoundation.org> References: <20180716073511.796555857@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds commit 0fa3ecd87848c9c93c2c828ef4c3a8ca36ce46c7 upstream. sgid directories have special semantics, making newly created files in the directory belong to the group of the directory, and newly created subdirectories will also become sgid. This is historically used for group-shared directories. But group directories writable by non-group members should not imply that such non-group members can magically join the group, so make sure to clear the sgid bit on non-directories for non-members (but remember that sgid without group execute means "mandatory locking", just to confuse things even more). Reported-by: Jann Horn Cc: Andy Lutomirski Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/inode.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/inode.c +++ b/fs/inode.c @@ -1937,8 +1937,14 @@ void inode_init_owner(struct inode *inod inode->i_uid = current_fsuid(); if (dir && dir->i_mode & S_ISGID) { inode->i_gid = dir->i_gid; + + /* Directories are special, and always inherit S_ISGID */ if (S_ISDIR(mode)) mode |= S_ISGID; + else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) && + !in_group_p(inode->i_gid) && + !capable_wrt_inode_uidgid(dir, CAP_FSETID)) + mode &= ~S_ISGID; } else inode->i_gid = current_fsgid(); inode->i_mode = mode;