linux-kernel - [PATCH v8 6/6] evm: Support multiple LSMs providing an xattr

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Date:   Tue, 14 Mar 2023 09:17:20 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com
Cc:     ocfs2-devel@....oracle.com, reiserfs-devel@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, keescook@...omium.org,
        nicolas.bouchinet@...p-os.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH v8 6/6] evm: Support multiple LSMs providing an xattr

From: Roberto Sassu <roberto.sassu@...wei.com>

Currently, evm_inode_init_security() processes a single LSM xattr from
the array passed by security_inode_init_security(), and calculates the
HMAC on it and other inode metadata.

Given that initxattrs() callbacks, called by
security_inode_init_security(), expect that this array is terminated when
the xattr name is set to NULL, reuse the same assumption to scan all xattrs
and to calculate the HMAC on all of them.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
Reviewed-by: Casey Schaufler <casey@...aufler-ca.com>
Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 security/integrity/evm/evm.h        |  2 ++
 security/integrity/evm/evm_crypto.c |  9 ++++++++-
 security/integrity/evm/evm_main.c   | 16 +++++++++++-----
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index f8b8c5004fc..f799d72a59f 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -46,6 +46,8 @@ struct evm_digest {
 	char digest[IMA_MAX_DIGEST_SIZE];
 } __packed;
 
+int evm_protected_xattr(const char *req_xattr_name);
+
 int evm_init_key(void);
 int evm_update_evmxattr(struct dentry *dentry,
 			const char *req_xattr_name,
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 033804f5a5f..5d8b5ecf594 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -389,6 +389,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 		  char *hmac_val)
 {
 	struct shash_desc *desc;
+	const struct xattr *xattr;
 
 	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 	if (IS_ERR(desc)) {
@@ -396,7 +397,13 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 		return PTR_ERR(desc);
 	}
 
-	crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
+	for (xattr = lsm_xattr; xattr->name != NULL; xattr++) {
+		if (!evm_protected_xattr(xattr->name))
+			continue;
+
+		crypto_shash_update(desc, xattr->value, xattr->value_len);
+	}
+
 	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
 	kfree(desc);
 	return 0;
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 7d20ce83915..013eb220cc5 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -305,7 +305,7 @@ static int evm_protected_xattr_common(const char *req_xattr_name,
 	return found;
 }
 
-static int evm_protected_xattr(const char *req_xattr_name)
+int evm_protected_xattr(const char *req_xattr_name)
 {
 	return evm_protected_xattr_common(req_xattr_name, false);
 }
@@ -870,10 +870,10 @@ int evm_inode_init_security(struct inode *inode, struct inode *dir,
 {
 	struct evm_xattr *xattr_data;
 	struct xattr *xattr, *evm_xattr;
+	bool evm_protected_xattrs = false;
 	int rc;
 
-	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs ||
-	    !evm_protected_xattr(xattrs->name))
+	if (!(evm_initialized & EVM_INIT_HMAC) || !xattrs)
 		return -EOPNOTSUPP;
 
 	/*
@@ -881,8 +881,14 @@ int evm_inode_init_security(struct inode *inode, struct inode *dir,
 	 * contiguous, there is enough space for security.evm, and that there is
 	 * a terminator at the end of the array.
 	 */
-	for (xattr = xattrs; xattr->name != NULL; xattr++)
-		;
+	for (xattr = xattrs; xattr->name != NULL; xattr++) {
+		if (evm_protected_xattr(xattr->name))
+			evm_protected_xattrs = true;
+	}
+
+	/* EVM xattr not needed. */
+	if (!evm_protected_xattrs)
+		return -EOPNOTSUPP;
 
 	evm_xattr = xattr;
 
-- 
2.25.1