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Thu, 17 Sep 2020 17:47:55 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CA65E4C046; Thu, 17 Sep 2020 17:47:53 +0000 (GMT) Received: from sig-9-65-208-105.ibm.com (unknown [9.65.208.105]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 17 Sep 2020 17:47:53 +0000 (GMT) Message-ID: Subject: Re: [PATCH v2 07/12] evm: Introduce EVM_RESET_STATUS atomic flag From: Mimi Zohar To: Roberto Sassu , "mjg59@google.com" , John Johansen Cc: "linux-integrity@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Silviu Vlasceanu , "stable@vger.kernel.org" Date: Thu, 17 Sep 2020 13:47:52 -0400 In-Reply-To: <581966c47e94412ab3fd5b2ca9aacd3d@huawei.com> References: <20200904092339.19598-1-roberto.sassu@huawei.com> <20200904092643.20013-3-roberto.sassu@huawei.com> <5bbf2169cfa38bb7a3d696e582c1de954a82d5c6.camel@linux.ibm.com> <581966c47e94412ab3fd5b2ca9aacd3d@huawei.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-12.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-09-17_12:2020-09-16,2020-09-17 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 clxscore=1015 adultscore=0 mlxscore=0 lowpriorityscore=0 suspectscore=3 bulkscore=0 priorityscore=1501 spamscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009170127 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2020-09-17 at 17:36 +0000, Roberto Sassu wrote: > > > diff --git a/security/integrity/evm/evm_main.c > > b/security/integrity/evm/evm_main.c > > > index 4e9f5e8b21d5..05be1ad3e6f3 100644 > > > --- a/security/integrity/evm/evm_main.c > > > +++ b/security/integrity/evm/evm_main.c > > > @@ -221,8 +221,15 @@ static enum integrity_status > > evm_verify_hmac(struct dentry *dentry, > > > evm_status = (rc == -ENODATA) ? > > > INTEGRITY_NOXATTRS : INTEGRITY_FAIL; > > > out: > > > - if (iint) > > > + if (iint) { > > > + /* > > > + * EVM_RESET_STATUS can be cleared only by > > evm_verifyxattr() > > > + * when EVM_ALLOW_METADATA_WRITES is set. This > > guarantees that > > > + * IMA sees the EVM_RESET_STATUS flag set before it is > > cleared. > > > + */ > > > + clear_bit(EVM_RESET_STATUS, &iint->atomic_flags); > > > iint->evm_status = evm_status; > > > > True IMA is currently the only caller of evm_verifyxattr() in the > > upstreamed kernel, but it is an exported function, which may be called > > from elsewhere. The previous version crossed the boundary between EVM > > & IMA with EVM modifying the IMA flag directly. This version assumes > > that IMA will be the only caller. Otherwise, I like this version. > > Ok, I think it is better, as you suggested, to export a new EVM function > that tells if evm_reset_status() will be executed in the EVM post hooks, and > to call this function from IMA. IMA would then call ima_reset_appraise_flags() > also depending on the result of the new EVM function. > > ima_reset_appraise_flags() should be called in a post hook in IMA. > Should I introduce it? Yes, so any callers of evm_verifyxattr() will need to implement the post hook as well. As much as possible, please limit code duplication. The last time I looked, there didn't seem to be a locking concern, but please make sure. thanks, Mimi