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Fri, 23 Feb 2024 17:25:26 +0000 (GMT) From: Stefan Berger To: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-unionfs@vger.kernel.org Cc: linux-kernel@vger.kernel.org, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, roberto.sassu@huawei.com, amir73il@gmail.com, brauner@kernel.org, miklos@szeredi.hu, Stefan Berger Subject: [PATCH v3 08/10] evm: Enforce signatures on unsupported filesystem for EVM_INIT_X509 Date: Fri, 23 Feb 2024 12:25:11 -0500 Message-ID: <20240223172513.4049959-9-stefanb@linux.ibm.com> X-Mailer: git-send-email 2.43.2 In-Reply-To: <20240223172513.4049959-1-stefanb@linux.ibm.com> References: <20240223172513.4049959-1-stefanb@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: zIW5Up1MKJQsuaoxHMKfwanSiqMdoDAB X-Proofpoint-ORIG-GUID: ttjXmNiwHXBpNfA2jly-K0dxoad2B2dx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-23_03,2024-02-23_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 phishscore=0 suspectscore=0 clxscore=1015 impostorscore=0 priorityscore=1501 adultscore=0 lowpriorityscore=0 mlxscore=0 spamscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2402230127 Unsupported filesystems currently do not enforce any signatures. Add support for signature enforcement of the "original" and "portable & immutable" signatures when EVM_INIT_X509 is enabled. The "original" signature type contains filesystem specific metadata. Thus it cannot be copied up and verified. However with EVM_INIT_X509 and EVM_ALLOW_METADATA_WRITES enabled, the "original" file signature may be written. When EVM_ALLOW_METADATA_WRITES is not set or once it is removed from /sys/kernel/security/evm by setting EVM_INIT_HMAC for example, it is not possible to write or remove xattrs on the overlay filesystem. This change still prevents EVM from writing HMAC signatures on unsupported filesystem when EVM_INIT_HMAC is enabled. Co-developed-by: Mimi Zohar Signed-off-by: Stefan Berger Signed-off-by: Mimi Zohar --- security/integrity/evm/evm_main.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index c1ca0894cd8a..cfb4f9809369 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -192,7 +192,11 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, iint->evm_status == INTEGRITY_PASS_IMMUTABLE)) return iint->evm_status; - if (is_unsupported_fs(dentry)) + /* + * On unsupported filesystems without EVM_INIT_X509 enabled, skip + * signature verification. + */ + if (!(evm_initialized & EVM_INIT_X509) && is_unsupported_fs(dentry)) return INTEGRITY_UNKNOWN; /* if status is not PASS, try to check again - against -ENOMEM */ @@ -261,7 +265,8 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, evm_status = INTEGRITY_PASS_IMMUTABLE; } else if (!IS_RDONLY(inode) && !(inode->i_sb->s_readonly_remount) && - !IS_IMMUTABLE(inode)) { + !IS_IMMUTABLE(inode) && + !is_unsupported_fs(dentry)) { evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len); @@ -419,9 +424,6 @@ enum integrity_status evm_verifyxattr(struct dentry *dentry, if (!evm_key_loaded() || !evm_protected_xattr(xattr_name)) return INTEGRITY_UNKNOWN; - if (is_unsupported_fs(dentry)) - return INTEGRITY_UNKNOWN; - return evm_verify_hmac(dentry, xattr_name, xattr_value, xattr_value_len); }