From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD958C433B4 for ; Fri, 23 Apr 2021 13:18:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 876E161445 for ; Fri, 23 Apr 2021 13:18:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242666AbhDWNSo (ORCPT ); Fri, 23 Apr 2021 09:18:44 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:53800 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242616AbhDWNSl (ORCPT ); Fri, 23 Apr 2021 09:18:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619183885; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ih5PcddgkKygbzS3OXVUA5ZjXGVsRuOHJshpqa5QHrs=; b=O5+D6seE1DSdbCXSLEloJ+IUWJrEmNC+r8HN4CEPMhi/oesip2rC1yQeUNAd9OLTCHF/On 5YfW/RYP7OWPNn3UKhfpO3SKFt6uD2IuFmmOQzX9VNfXixwVRAt5Q1pqrY9ibhrRBn7wJE kgQucPUePhRJABMWlnhu1o6THhdoP+8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-291-uOFyxz9qMh2BrwhMGOevgw-1; Fri, 23 Apr 2021 09:18:01 -0400 X-MC-Unique: uOFyxz9qMh2BrwhMGOevgw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3B4E1817477; Fri, 23 Apr 2021 13:17:55 +0000 (UTC) Received: from t480s.redhat.com (ovpn-112-41.ams2.redhat.com [10.36.112.41]) by smtp.corp.redhat.com (Postfix) with ESMTP id 340BB60BE5; Fri, 23 Apr 2021 13:17:36 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Alexander Viro , Alexey Dobriyan , Steven Rostedt , Peter Zijlstra , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Petr Mladek , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , Kees Cook , "Eric W. Biederman" , Greg Ungerer , Geert Uytterhoeven , Mike Rapoport , Vlastimil Babka , Vincenzo Frascino , Chinwen Chang , Michel Lespinasse , Catalin Marinas , "Matthew Wilcox (Oracle)" , Huang Ying , Jann Horn , Feng Tang , Kevin Brodsky , Michael Ellerman , Shawn Anastasio , Steven Price , Nicholas Piggin , Christian Brauner , Jens Axboe , Gabriel Krisman Bertazi , Peter Xu , Suren Baghdasaryan , Shakeel Butt , Marco Elver , Daniel Jordan , Nicolas Viennot , Thomas Cedeno , Collin Fijalkovich , Michal Hocko , linux-api@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH RFC 3/7] kernel/fork: always deny write access to current MM exe_file Date: Fri, 23 Apr 2021 15:16:36 +0200 Message-Id: <20210423131640.20080-4-david@redhat.com> In-Reply-To: <20210423131640.20080-1-david@redhat.com> References: <20210423131640.20080-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We want to remove VM_DENYWRITE only currently only used when mapping the executable during exec. During exec, we already deny_write_access() the executable, however, after exec completes the VMAs mapped with VM_DENYWRITE effectively keeps write access denied via deny_write_access(). Let's deny write access when setting the MM exe_file. With this change, we can remove VM_DENYWRITE for mapping executables. This represents a minor user space visible change: sys_prctl(PR_SET_MM_EXE_FILE) can now fail if the file is already opened writable. Also, after sys_prctl(PR_SET_MM_EXE_FILE), the file cannot be opened writable. Note that we can already fail with -EACCES if the file doesn't have execute permissions. Signed-off-by: David Hildenbrand --- kernel/fork.c | 39 ++++++++++++++++++++++++++++++++++----- 1 file changed, 34 insertions(+), 5 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 199463625adc..0681f2973667 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -472,6 +472,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, { struct vm_area_struct *mpnt, *tmp, *prev, **pprev; struct rb_node **rb_link, *rb_parent; + struct file *exe_file; int retval; unsigned long charge; LIST_HEAD(uf); @@ -489,7 +490,10 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING); /* No ordering required: file already has been exposed. */ - RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm)); + exe_file = get_mm_exe_file(oldmm); + RCU_INIT_POINTER(mm->exe_file, exe_file); + if (exe_file) + deny_write_access(exe_file); mm->total_vm = oldmm->total_vm; mm->data_vm = oldmm->data_vm; @@ -634,8 +638,13 @@ static inline void mm_free_pgd(struct mm_struct *mm) #else static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) { + struct file *exe_file; + mmap_write_lock(oldmm); - RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm)); + exe_file = get_mm_exe_file(oldmm); + RCU_INIT_POINTER(mm->exe_file, exe_file); + if (exe_file) + deny_write_access(exe_file); mmap_write_unlock(oldmm); return 0; } @@ -1152,11 +1161,19 @@ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) */ old_exe_file = rcu_dereference_raw(mm->exe_file); - if (new_exe_file) + if (new_exe_file) { get_file(new_exe_file); + /* + * exec code is required to deny_write_access() successfully, + * so this cannot fail + */ + deny_write_access(new_exe_file); + } rcu_assign_pointer(mm->exe_file, new_exe_file); - if (old_exe_file) + if (old_exe_file) { + allow_write_access(old_exe_file); fput(old_exe_file); + } } int atomic_set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) @@ -1183,10 +1200,22 @@ int atomic_set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) } /* set the new file, lockless */ + ret = deny_write_access(new_exe_file); + if (ret) + return -EACCES; get_file(new_exe_file); + old_exe_file = xchg(&mm->exe_file, new_exe_file); - if (old_exe_file) + if (old_exe_file) { + /* + * Don't race with dup_mmap() getting the file and disallowing + * write access while someone might open the file writable. + */ + mmap_read_lock(mm); + allow_write_access(old_exe_file); fput(old_exe_file); + mmap_read_unlock(mm); + } return 0; } -- 2.30.2