From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f175.google.com (mail-pf0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id 5DA2382F82 for ; Thu, 10 Dec 2015 02:06:44 -0500 (EST) Received: by pfu207 with SMTP id 207so43399365pfu.2 for ; Wed, 09 Dec 2015 23:06:44 -0800 (PST) Received: from 1wt.eu (wtarreau.pck.nerim.net. [62.212.114.60]) by mx.google.com with ESMTP id lf12si18400821pab.22.2015.12.09.23.06.41 for ; Wed, 09 Dec 2015 23:06:42 -0800 (PST) Date: Thu, 10 Dec 2015 08:06:35 +0100 From: Willy Tarreau Subject: Re: [PATCH v5] fs: clear file privilege bits when mmap writing Message-ID: <20151210070635.GC31922@1wt.eu> References: <20151209225148.GA14794@www.outflux.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151209225148.GA14794@www.outflux.net> Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: Andrew Morton , Jan Kara , yalin wang , "Eric W. Biederman" , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Kees, Why not add a new file flag instead ? Something like this (editing your patch by hand to illustrate) : diff --git a/fs/file_table.c b/fs/file_table.c index ad17e05ebf95..3a7eee76ea90 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -191,6 +191,17 @@ static void __fput(struct file *file) might_sleep(); + /* + * XXX: While avoiding mmap_sem, we've already been written to. + * We must ignore the return value, since we can't reject the + * write. + */ + if (unlikely(file->f_flags & FL_DROP_PRIVS)) { + mutex_lock(&inode->i_mutex); + file_remove_privs(file); + mutex_unlock(&inode->i_mutex); + } + fsnotify_close(file); /* * The function eventpoll_release() should be the first called diff --git a/include/linux/fs.h b/include/linux/fs.h index 3aa514254161..409bd7047e7e 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -913,3 +913,4 @@ #define FL_OFDLCK 1024 /* lock is "owned" by struct file */ #define FL_LAYOUT 2048 /* outstanding pNFS layout */ +#define FL_DROP_PRIVS 4096 /* lest something weird decides that 2 is OK */ diff --git a/mm/memory.c b/mm/memory.c index c387430f06c3..08a77e0cf65f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2036,6 +2036,7 @@ static inline int wp_page_reuse(struct mm_struct *mm, if (!page_mkwrite) file_update_time(vma->vm_file); + vma->vm_file->f_flags |= FL_DROP_PRIVS; } return VM_FAULT_WRITE; Willy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org