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Wed, 04 Dec 2024 19:25:23 +0000 Received: from smtpav06.fra02v.mail.ibm.com (smtpav06.fra02v.mail.ibm.com [10.20.54.105]) by smtprelay04.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 4B4JPLtY30802616 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 4 Dec 2024 19:25:21 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4935820049; Wed, 4 Dec 2024 19:25:21 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 87D4320040; Wed, 4 Dec 2024 19:25:19 +0000 (GMT) Received: from li-43857255-d5e6-4659-90f1-fc5cee4750ad.watson.ibm.com (unknown [9.31.103.152]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 4 Dec 2024 19:25:19 +0000 (GMT) From: Mimi Zohar To: linux-integrity@vger.kernel.org Cc: Mimi Zohar , =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , roberto.sassu@huawei.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Xu , Kees Cook , Paul Moore , audit@vger.kernel.org Subject: [PATCH v2] ima: instantiate the bprm_creds_for_exec() hook Date: Wed, 4 Dec 2024 14:25:14 -0500 Message-ID: <20241204192514.40308-1-zohar@linux.ibm.com> X-Mailer: git-send-email 2.47.0 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: iOqdpHeouk3A7X1sMprDgAJHPij2y0EY X-Proofpoint-ORIG-GUID: iOqdpHeouk3A7X1sMprDgAJHPij2y0EY X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 phishscore=0 clxscore=1015 priorityscore=1501 adultscore=0 mlxscore=0 lowpriorityscore=0 spamscore=0 malwarescore=0 impostorscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2411120000 definitions=main-2412040145 Like direct file execution (e.g. ./script.sh), indirect file execution (e.g. sh script.sh) needs to be measured and appraised. Instantiate the new security_bprm_creds_for_exec() hook to measure and verify the indirect file's integrity. Unlike direct file execution, indirect file execution is optionally enforced by the interpreter. Differentiate kernel and userspace enforced integrity audit messages. Co-developed-by: Roberto Sassu Signed-off-by: Roberto Sassu Signed-off-by: Mimi Zohar --- Changelog v3: - Mickael: add comment ima_bprm_creds_for_exec(), minor code cleanup, add Co-developed-by tag. Changelog v2: - Mickael: Use same audit messages with new audit message number - Stefan Berger: Return boolean from is_bprm_creds_for_exec() include/uapi/linux/audit.h | 1 + security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++++-- security/integrity/ima/ima_main.c | 29 +++++++++++++++++++++++++++ 3 files changed, 55 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h index 75e21a135483..826337905466 100644 --- a/include/uapi/linux/audit.h +++ b/include/uapi/linux/audit.h @@ -161,6 +161,7 @@ #define AUDIT_INTEGRITY_RULE 1805 /* policy rule */ #define AUDIT_INTEGRITY_EVM_XATTR 1806 /* New EVM-covered xattr */ #define AUDIT_INTEGRITY_POLICY_RULE 1807 /* IMA policy rules */ +#define AUDIT_INTEGRITY_DATA_CHECK 1808 /* Userspace enforced data integrity */ #define AUDIT_KERNEL 2000 /* Asynchronous audit record. NOT A REQUEST. */ diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index 656c709b974f..fc0d1f3cceca 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include @@ -469,6 +470,17 @@ int ima_check_blacklist(struct ima_iint_cache *iint, return rc; } +static bool is_bprm_creds_for_exec(enum ima_hooks func, struct file *file) +{ + struct linux_binprm *bprm; + + if (func == BPRM_CHECK) { + bprm = container_of(&file, struct linux_binprm, file); + return bprm->is_check; + } + return false; +} + /* * ima_appraise_measurement - appraise file measurement * @@ -483,6 +495,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, int xattr_len, const struct modsig *modsig) { static const char op[] = "appraise_data"; + int audit_msgno = AUDIT_INTEGRITY_DATA; const char *cause = "unknown"; struct dentry *dentry = file_dentry(file); struct inode *inode = d_backing_inode(dentry); @@ -494,6 +507,16 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, if (!(inode->i_opflags & IOP_XATTR) && !try_modsig) return INTEGRITY_UNKNOWN; + /* + * Unlike any of the other LSM hooks where the kernel enforces file + * integrity, enforcing file integrity for the bprm_creds_for_exec() + * LSM hook with the AT_EXECVE_CHECK flag is left up to the discretion + * of the script interpreter(userspace). Differentiate kernel and + * userspace enforced integrity audit messages. + */ + if (is_bprm_creds_for_exec(func, file)) + audit_msgno = AUDIT_INTEGRITY_DATA_CHECK; + /* If reading the xattr failed and there's no modsig, error out. */ if (rc <= 0 && !try_modsig) { if (rc && rc != -ENODATA) @@ -569,7 +592,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, (iint->flags & IMA_FAIL_UNVERIFIABLE_SIGS))) { status = INTEGRITY_FAIL; cause = "unverifiable-signature"; - integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, + integrity_audit_msg(audit_msgno, inode, filename, op, cause, rc, 0); } else if (status != INTEGRITY_PASS) { /* Fix mode, but don't replace file signatures. */ @@ -589,7 +612,7 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint, status = INTEGRITY_PASS; } - integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename, + integrity_audit_msg(audit_msgno, inode, filename, op, cause, rc, 0); } else { ima_cache_flags(iint, func); diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 06132cf47016..5d4ac8aa2f1f 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -554,6 +554,34 @@ static int ima_bprm_check(struct linux_binprm *bprm) MAY_EXEC, CREDS_CHECK); } +/** + * ima_bprm_creds_for_exec - collect/store/appraise measurement. + * @bprm: contains the linux_binprm structure + * + * Based on the IMA policy and the execvat(2) AT_EXECVE_CHECK flag, measure + * and appraise the integrity of a file to be executed by script interpreters. + * Unlike any of the other LSM hooks where the kernel enforces file integrity, + * enforcing file integrity is left up to the discretion of the script + * interpreter (userspace). + * + * On success return 0. On integrity appraisal error, assuming the file + * is in policy and IMA-appraisal is in enforcing mode, return -EACCES. + */ +static int ima_bprm_creds_for_exec(struct linux_binprm *bprm) +{ + /* + * As security_bprm_check() is called multiple times, both + * the script and the shebang interpreter are measured, appraised, + * and audited. Limit usage of this LSM hook to just measuring, + * appraising, and auditing the indirect script execution + * (e.g. ./sh example.sh). + */ + if (!bprm->is_check) + return 0; + + return ima_bprm_check(bprm); +} + /** * ima_file_check - based on policy, collect/store measurement. * @file: pointer to the file to be measured @@ -1177,6 +1205,7 @@ static int __init init_ima(void) static struct security_hook_list ima_hooks[] __ro_after_init = { LSM_HOOK_INIT(bprm_check_security, ima_bprm_check), + LSM_HOOK_INIT(bprm_creds_for_exec, ima_bprm_creds_for_exec), LSM_HOOK_INIT(file_post_open, ima_file_check), LSM_HOOK_INIT(inode_post_create_tmpfile, ima_post_create_tmpfile), LSM_HOOK_INIT(file_release, ima_file_free),