From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:56772 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750738AbeBUW5z (ORCPT ); Wed, 21 Feb 2018 17:57:55 -0500 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1LMnH5v069163 for ; Wed, 21 Feb 2018 17:57:55 -0500 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0a-001b2d01.pphosted.com with ESMTP id 2g9eg87rae-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 21 Feb 2018 17:57:54 -0500 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Feb 2018 22:57:52 -0000 Subject: Re: [PATCH v1 1/2] ima: fail signature verification on untrusted filesystems From: Mimi Zohar To: "Eric W. Biederman" Cc: "Serge E. Hallyn" , James Morris , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Miklos Szeredi , Seth Forshee , Dongsu Park , Alban Crequy Date: Wed, 21 Feb 2018 17:57:47 -0500 In-Reply-To: <87mv02c65y.fsf@xmission.com> References: <1519053483-18396-1-git-send-email-zohar@linux.vnet.ibm.com> <1519053483-18396-2-git-send-email-zohar@linux.vnet.ibm.com> <87zi44mz26.fsf@xmission.com> <87tvucifji.fsf@xmission.com> <1519135329.3736.88.camel@linux.vnet.ibm.com> <20180220201636.GA1565@mail.hallyn.com> <1519224379.3736.154.camel@linux.vnet.ibm.com> <87mv02c65y.fsf@xmission.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Message-Id: <1519253867.19593.25.camel@linux.vnet.ibm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, 2018-02-21 at 16:46 -0600, Eric W. Biederman wrote: > Mimi Zohar writes: > > >> > > On the flip side when it really is a trusted mounter, and it is in a > >> > > configuration that IMA has a reasonable expectation of seeing all of > >> > > the changes it would be nice if we can say please trust this mount. > >> > > >> > IMA has no way of detecting file change.  This was one of the reasons > >> > for the original patch set's not using the cached IMA results. > >> > > >> > Even in the case of a trusted mounter and not using IMA cached > >> > results, there are no guarantees that the data read to calculate the > >> > file hash, will be the same as what is subsequently read.  In some > >> > environments this might be an acceptable risk, while in others not. > >> > >> So for the cases where it's not, there should be an IMA option or policy > >> to say any SB_I_IMA_UNVERIFIABLE_SIGNATURES mounts should be not > >> trusted, with the default being both SB_I_IMA_UNVERIFIABLE_SIGNATURES and > >> SB_I_UNTRUSTED_MOUNTER must be true to not trust, right? > > > > Right.  To summarize, we've identified 3 scenarios: > > 1. Fail signature verification on unprivileged non-init root mounted > > file systems. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES and SB_I_UNTRUSTED_MOUNTER > > (always enabled) > > > > 2. Permit signature verification on privileged file system mounts in a > > secure system environment.  Willing to accept the risk.  Does not rely > > on cached integrity results, but forces re-evaluation. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES, not SB_I_UNTRUSTED_MOUNTER or > > IMA_FAIL_UNVERIFICABLE_SIGNATURES (default behavior) > > > > 3. Fail signature verification also on privileged file system mounts. > > Fail safe, unwilling to accept the risk. > > > > flags: > > SB_I_IMA_UNVERIFIABLE_SIGNATURES and IMA_FAIL_UNVERIFIABLE_SIGNATURES > > > > Enabled by specifying "ima_policy=unverifiable_sigs" on the boot > > command line. > > There is another scenaro. > 4. Permit signature verification on out of kernel but otherwise fully > capable and trusted filesystems. > > Fuse has a mode where it appears to be cache coherent, and guaranteed to > be local. AKA when fuse block is used and FUSE_WRITEBACK_CACHE is set. > That configuratioin plus the the allow_other mount option appear to > signal a fuse mount that can be reasonably be trusted as much as an > in-kernel block based filesystem. > > That is a mode someone might use to mount exFat or ntfs-3g. > > As all writes come from the kernel, and it is safe to have a write-back > cache I believe ima can reasonably verify signatures. There may be > something technical like the need to verify i_version in this case, > but for purposes of argument let's say fuse has implemented all of the > necessary technical details. > > In that case we have a case where it is reasonable to say that > SB_I_IMA_UNVERIFIABLE_SIGNATURES would be incorrect to set on a fuse > filesystem. > > Mimi do you agree or am I missing something? This simply sounds like a performance improvement to the second scenario, where instead of *always* forcing re-validation, it checks the i_version.  Perhaps based on a different flag. Mimi  From mboxrd@z Thu Jan 1 00:00:00 1970 From: zohar@linux.vnet.ibm.com (Mimi Zohar) Date: Wed, 21 Feb 2018 17:57:47 -0500 Subject: [PATCH v1 1/2] ima: fail signature verification on untrusted filesystems In-Reply-To: <87mv02c65y.fsf@xmission.com> References: <1519053483-18396-1-git-send-email-zohar@linux.vnet.ibm.com> <1519053483-18396-2-git-send-email-zohar@linux.vnet.ibm.com> <87zi44mz26.fsf@xmission.com> <87tvucifji.fsf@xmission.com> <1519135329.3736.88.camel@linux.vnet.ibm.com> <20180220201636.GA1565@mail.hallyn.com> <1519224379.3736.154.camel@linux.vnet.ibm.com> <87mv02c65y.fsf@xmission.com> Message-ID: <1519253867.19593.25.camel@linux.vnet.ibm.com> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org On Wed, 2018-02-21 at 16:46 -0600, Eric W. Biederman wrote: > Mimi Zohar writes: > > >> > > On the flip side when it really is a trusted mounter, and it is in a > >> > > configuration that IMA has a reasonable expectation of seeing all of > >> > > the changes it would be nice if we can say please trust this mount. > >> > > >> > IMA has no way of detecting file change. ?This was one of the reasons > >> > for the original patch set's not using the cached IMA results. > >> > > >> > Even in the case of a trusted mounter and not using IMA cached > >> > results, there are no guarantees that the data read to calculate the > >> > file hash, will be the same as what is subsequently read. ?In some > >> > environments this might be an acceptable risk, while in others not. > >> > >> So for the cases where it's not, there should be an IMA option or policy > >> to say any SB_I_IMA_UNVERIFIABLE_SIGNATURES mounts should be not > >> trusted, with the default being both SB_I_IMA_UNVERIFIABLE_SIGNATURES and > >> SB_I_UNTRUSTED_MOUNTER must be true to not trust, right? > > > > Right. ?To summarize, we've identified 3 scenarios: > > 1. Fail signature verification on unprivileged non-init root mounted > > file systems. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES and SB_I_UNTRUSTED_MOUNTER > > (always enabled) > > > > 2. Permit signature verification on privileged file system mounts in a > > secure system environment. ?Willing to accept the risk. ?Does not rely > > on cached integrity results, but forces re-evaluation. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES, not SB_I_UNTRUSTED_MOUNTER or > > IMA_FAIL_UNVERIFICABLE_SIGNATURES (default behavior) > > > > 3. Fail signature verification also on privileged file system mounts. > > Fail safe, unwilling to accept the risk. > > > > flags: > > SB_I_IMA_UNVERIFIABLE_SIGNATURES and IMA_FAIL_UNVERIFIABLE_SIGNATURES > > > > Enabled by specifying "ima_policy=unverifiable_sigs" on the boot > > command line. > > There is another scenaro. > 4. Permit signature verification on out of kernel but otherwise fully > capable and trusted filesystems. > > Fuse has a mode where it appears to be cache coherent, and guaranteed to > be local. AKA when fuse block is used and FUSE_WRITEBACK_CACHE is set. > That configuratioin plus the the allow_other mount option appear to > signal a fuse mount that can be reasonably be trusted as much as an > in-kernel block based filesystem. > > That is a mode someone might use to mount exFat or ntfs-3g. > > As all writes come from the kernel, and it is safe to have a write-back > cache I believe ima can reasonably verify signatures. There may be > something technical like the need to verify i_version in this case, > but for purposes of argument let's say fuse has implemented all of the > necessary technical details. > > In that case we have a case where it is reasonable to say that > SB_I_IMA_UNVERIFIABLE_SIGNATURES would be incorrect to set on a fuse > filesystem. > > Mimi do you agree or am I missing something? This simply sounds like a performance improvement to the second scenario, where instead of *always* forcing re-validation, it checks the i_version. ?Perhaps based on a different flag. Mimi? -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:60154 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750752AbeBUW54 (ORCPT ); Wed, 21 Feb 2018 17:57:56 -0500 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1LMtvaE061936 for ; Wed, 21 Feb 2018 17:57:55 -0500 Received: from e06smtp13.uk.ibm.com (e06smtp13.uk.ibm.com [195.75.94.109]) by mx0a-001b2d01.pphosted.com with ESMTP id 2g9cprvkpb-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 21 Feb 2018 17:57:55 -0500 Received: from localhost by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Feb 2018 22:57:52 -0000 Subject: Re: [PATCH v1 1/2] ima: fail signature verification on untrusted filesystems From: Mimi Zohar To: "Eric W. Biederman" Cc: "Serge E. Hallyn" , James Morris , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Miklos Szeredi , Seth Forshee , Dongsu Park , Alban Crequy Date: Wed, 21 Feb 2018 17:57:47 -0500 In-Reply-To: <87mv02c65y.fsf@xmission.com> References: <1519053483-18396-1-git-send-email-zohar@linux.vnet.ibm.com> <1519053483-18396-2-git-send-email-zohar@linux.vnet.ibm.com> <87zi44mz26.fsf@xmission.com> <87tvucifji.fsf@xmission.com> <1519135329.3736.88.camel@linux.vnet.ibm.com> <20180220201636.GA1565@mail.hallyn.com> <1519224379.3736.154.camel@linux.vnet.ibm.com> <87mv02c65y.fsf@xmission.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Message-Id: <1519253867.19593.25.camel@linux.vnet.ibm.com> Sender: linux-integrity-owner@vger.kernel.org List-ID: On Wed, 2018-02-21 at 16:46 -0600, Eric W. Biederman wrote: > Mimi Zohar writes: > > >> > > On the flip side when it really is a trusted mounter, and it is in a > >> > > configuration that IMA has a reasonable expectation of seeing all of > >> > > the changes it would be nice if we can say please trust this mount. > >> > > >> > IMA has no way of detecting file change. This was one of the reasons > >> > for the original patch set's not using the cached IMA results. > >> > > >> > Even in the case of a trusted mounter and not using IMA cached > >> > results, there are no guarantees that the data read to calculate the > >> > file hash, will be the same as what is subsequently read. In some > >> > environments this might be an acceptable risk, while in others not. > >> > >> So for the cases where it's not, there should be an IMA option or policy > >> to say any SB_I_IMA_UNVERIFIABLE_SIGNATURES mounts should be not > >> trusted, with the default being both SB_I_IMA_UNVERIFIABLE_SIGNATURES and > >> SB_I_UNTRUSTED_MOUNTER must be true to not trust, right? > > > > Right. To summarize, we've identified 3 scenarios: > > 1. Fail signature verification on unprivileged non-init root mounted > > file systems. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES and SB_I_UNTRUSTED_MOUNTER > > (always enabled) > > > > 2. Permit signature verification on privileged file system mounts in a > > secure system environment. Willing to accept the risk. Does not rely > > on cached integrity results, but forces re-evaluation. > > > > flags: SB_I_IMA_UNVERIFIABLE_SIGNATURES, not SB_I_UNTRUSTED_MOUNTER or > > IMA_FAIL_UNVERIFICABLE_SIGNATURES (default behavior) > > > > 3. Fail signature verification also on privileged file system mounts. > > Fail safe, unwilling to accept the risk. > > > > flags: > > SB_I_IMA_UNVERIFIABLE_SIGNATURES and IMA_FAIL_UNVERIFIABLE_SIGNATURES > > > > Enabled by specifying "ima_policy=unverifiable_sigs" on the boot > > command line. > > There is another scenaro. > 4. Permit signature verification on out of kernel but otherwise fully > capable and trusted filesystems. > > Fuse has a mode where it appears to be cache coherent, and guaranteed to > be local. AKA when fuse block is used and FUSE_WRITEBACK_CACHE is set. > That configuratioin plus the the allow_other mount option appear to > signal a fuse mount that can be reasonably be trusted as much as an > in-kernel block based filesystem. > > That is a mode someone might use to mount exFat or ntfs-3g. > > As all writes come from the kernel, and it is safe to have a write-back > cache I believe ima can reasonably verify signatures. There may be > something technical like the need to verify i_version in this case, > but for purposes of argument let's say fuse has implemented all of the > necessary technical details. > > In that case we have a case where it is reasonable to say that > SB_I_IMA_UNVERIFIABLE_SIGNATURES would be incorrect to set on a fuse > filesystem. > > Mimi do you agree or am I missing something? This simply sounds like a performance improvement to the second scenario, where instead of *always* forcing re-validation, it checks the i_version. Perhaps based on a different flag. Mimi