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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17AC7C54EBD for ; Fri, 13 Jan 2023 10:57:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241403AbjAMK5c (ORCPT ); Fri, 13 Jan 2023 05:57:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56454 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241303AbjAMK4x (ORCPT ); Fri, 13 Jan 2023 05:56:53 -0500 Received: from frasgout11.his.huawei.com (frasgout11.his.huawei.com [14.137.139.23]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C77F67A218; Fri, 13 Jan 2023 02:53:15 -0800 (PST) Received: from mail02.huawei.com (unknown [172.18.147.229]) by frasgout11.his.huawei.com (SkyGuard) with ESMTP id 4NtdNj4W7Fz9xFPt; Fri, 13 Jan 2023 18:45:25 +0800 (CST) Received: from roberto-ThinkStation-P620 (unknown [10.204.63.22]) by APP2 (Coremail) with SMTP id GxC2BwDnvGMGOMFj4RKRAA--.11240S2; Fri, 13 Jan 2023 11:53:02 +0100 (CET) Message-ID: Subject: Re: [PATCH v2] security: Restore passing final prot to ima_file_mmap() From: Roberto Sassu To: Mimi Zohar , Paul Moore Cc: jmorris@namei.org, serge@hallyn.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, Roberto Sassu , stable@vger.kernel.org Date: Fri, 13 Jan 2023 11:52:51 +0100 In-Reply-To: <058f1bdf4ba75c3a00918cefbf1be32477b51639.camel@linux.ibm.com> References: <20221221141007.2579770-1-roberto.sassu@huaweicloud.com> <4b8688ee3d533d989196004d5f9f2c7eb4093f8b.camel@huaweicloud.com> <058f1bdf4ba75c3a00918cefbf1be32477b51639.camel@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-CM-TRANSID: GxC2BwDnvGMGOMFj4RKRAA--.11240S2 X-Coremail-Antispam: 1UD129KBjvJXoW3Gw1xArWrWF1UJrW8tr4UCFg_yoW7Cr4rpF W5ta4jkr4kJFyFyrn2v3W3uFyFk39rKa4UWF1qgry8Ar1qgF1akr13AFWj9Fy8XrykW3WU Zw17KrW3X3WqyaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUk0b4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Jr0_JF4l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Jr0_Gr1l84ACjcxK6I8E87Iv67AKxVW8JVWxJwA2z4x0Y4vEx4A2jsIEc7CjxV AFwI0_Gr0_Gr1UM2AIxVAIcxkEcVAq07x20xvEncxIr21l5I8CrVACY4xI64kE6c02F40E x7xfMcIj6xIIjxv20xvE14v26r1j6r18McIj6I8E87Iv67AKxVWUJVW8JwAm72CE4IkC6x 0Yz7v_Jr0_Gr1lF7xvr2IY64vIr41lFIxGxcIEc7CjxVA2Y2ka0xkIwI1l42xK82IYc2Ij 64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x 8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIYrxkI7VAKI48JMIIF0xvE 2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42 xK8VAvwI8IcIk0rVWrJr0_WFyUJwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv 6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUrR6zUUUUU X-CM-SenderInfo: purev21wro2thvvxqx5xdzvxpfor3voofrz/1tbiAQAQBF1jj4eO+AAAsV X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2023-01-12 at 12:45 -0500, Mimi Zohar wrote: > On Thu, 2023-01-12 at 13:36 +0100, Roberto Sassu wrote: > > On Wed, 2023-01-11 at 09:25 -0500, Paul Moore wrote: > > > On Wed, Jan 11, 2023 at 4:31 AM Roberto Sassu > > > wrote: > > > > On Fri, 2023-01-06 at 16:14 -0500, Paul Moore wrote: > > > > > On Wed, Dec 21, 2022 at 9:10 AM Roberto Sassu > > > > > wrote: > > > > > > From: Roberto Sassu > > > > > > > > > > > > Commit 98de59bfe4b2f ("take calculation of final prot in > > > > > > security_mmap_file() into a helper") moved the code to update prot with the > > > > > > actual protection flags to be granted to the requestor by the kernel to a > > > > > > helper called mmap_prot(). However, the patch didn't update the argument > > > > > > passed to ima_file_mmap(), making it receive the requested prot instead of > > > > > > the final computed prot. > > > > > > > > > > > > A possible consequence is that files mmapped as executable might not be > > > > > > measured/appraised if PROT_EXEC is not requested but subsequently added in > > > > > > the final prot. > > > > > > > > > > > > Replace prot with mmap_prot(file, prot) as the second argument of > > > > > > ima_file_mmap() to restore the original behavior. > > > > > > > > > > > > Cc: stable@vger.kernel.org > > > > > > Fixes: 98de59bfe4b2 ("take calculation of final prot in security_mmap_file() into a helper") > > > > > > Signed-off-by: Roberto Sassu > > > > > > --- > > > > > > security/security.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/security/security.c b/security/security.c > > > > > > index d1571900a8c7..0d2359d588a1 100644 > > > > > > --- a/security/security.c > > > > > > +++ b/security/security.c > > > > > > @@ -1666,7 +1666,7 @@ int security_mmap_file(struct file *file, unsigned long prot, > > > > > > mmap_prot(file, prot), flags); > > > > > > if (ret) > > > > > > return ret; > > > > > > - return ima_file_mmap(file, prot); > > > > > > + return ima_file_mmap(file, mmap_prot(file, prot)); > > > > > > } > > > > > > > > > > This seems like a reasonable fix, although as the original commit is > > > > > ~10 years old at this point I am a little concerned about the impact > > > > > this might have on IMA. Mimi, what do you think? > > > > As a user, I probably would like to know that my system is not > > measuring what it is supposed to measure. The rule: > > Agreed, that it is measuring what it is supposed to measure. > > > measure func=MMAP_CHECK mask=MAY_EXEC > > > > is looking for executable code mapped in memory. If it is requested by > > the application or the kernel, probably it does not make too much > > difference from the perspective of measurement goals. > > Currently, it's limited to measuring file's being mmapped. From what I > can tell from looking at the code, additional measurements would be > included when "current->personality & READ_IMPLIES_EXEC". Yes, I developed a small program to see the differences: void main() { struct stat st; personality(READ_IMPLIES_EXEC); stat("test-file", &st); int fd = open("test-file", O_RDONLY); mmap(0, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0); } Without the patch, the test-file measurement does not appear. > > If we add a new policy keyword, existing policies would not be updated > > unless the system administrator notices it. If a remote attestation > > fails, the administrator has to look into it. > > Verifying the measurement list against a TPM quote should work > regardless of additional measurements. The attestation server, > however, should also check for unknown files. > > > Maybe we can introduce a new hook called MMAP_CHECK_REQ, so that an > > administrator could change the policy to have the current behavior, if > > the administrator wishes so. > > Agreed, for backwards compatibility this would be good. Would you > support it afterward transitioning IMA to an LSM? Yes, I have a patch to align ima_file_mmap() with the mmap_file() hook definition: -int ima_file_mmap(struct file *file, unsigned long prot) +int ima_file_mmap(struct file *file, unsigned long reqprot, + unsigned long prot, unsigned long flags) This would have also fixed the issue. But for backporting, I did a standalone patch. I noticed that Kees found this as well: -int ima_file_mmap(struct file *file, unsigned long prot) +static int ima_file_mmap(struct file *file, unsigned long reqprot, + unsigned long prot, unsigned long flags) { u32 secid; - if (file && (prot & PROT_EXEC)) { + if (file && (reqprot & PROT_EXEC)) { but from the history I saw that the original intent was to consider prot, not reqprot. > However "_REQ" could mean either requested or required. It was to recall reqprot. I could rename to MMAP_CHECK_REQPROT. Thanks Roberto > > > > > Beyond that, my only other comment would be to only call mmap_prot() > > > > > once and cache the results in a local variable. You could also fix up > > > > > some of the ugly indentation crimes in security_mmap_file() while you > > > > > are at it, e.g. something like this: > > > > > > > > Hi Paul > > > > > > > > thanks for the comments. With the patch set to move IMA and EVM to the > > > > LSM infrastructure we will be back to calling mmap_prot() only once, > > > > but I guess we could do anyway, as the patch (if accepted) would be > > > > likely backported to stable kernels. > > > > > > I think there is value in fixing this now and keeping it separate from > > > the IMA-to-LSM work as they really are disjoint. > > >