linux-kernel - [PATCH v2 3/9] evm: Implement per signature type decision in security_inode_copy_up

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Mon,  5 Feb 2024 13:25:00 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-unionfs@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, zohar@...ux.ibm.com, roberto.sassu@...wei.com,
        amir73il@...il.com, brauner@...nel.org, miklos@...redi.hu,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH v2 3/9] evm: Implement per signature type decision in security_inode_copy_up_xattr

To support portable and immutable signatures on otherwise unsupported
filesystems, determine the EVM signature type by the content of a file's
xattr. If the file has the appropriate signature then allow it to be
copied up. All other signature types are discarded as before.

"Portable and immutable" EVM signatures can be copied up by stacked file-
systems since the metadata their signature covers does not include file-
system-specific data such as a file's inode number, generation, and UUID.

Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 security/integrity/evm/evm_main.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 2555aa4501ae..565c36471408 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -898,9 +898,34 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
 
 int evm_inode_copy_up_xattr(struct dentry *src, const char *name)
 {
-	if (strcmp(name, XATTR_NAME_EVM) == 0)
-		return 1; /* Discard */
-	return -EOPNOTSUPP;
+	struct evm_ima_xattr_data *xattr_data = NULL;
+	int rc;
+
+	if (strcmp(name, XATTR_NAME_EVM) != 0)
+		return -EOPNOTSUPP;
+
+	/* first need to know the sig type */
+	rc = vfs_getxattr_alloc(&nop_mnt_idmap, src, XATTR_NAME_EVM,
+				(char **)&xattr_data, 0, GFP_NOFS);
+	if (rc <= 0)
+		return -EPERM;
+
+	if (rc < offsetof(struct evm_ima_xattr_data, type) +
+		 sizeof(xattr_data->type))
+		return -EPERM;
+
+	switch (xattr_data->type) {
+	case EVM_XATTR_PORTABLE_DIGSIG:
+		rc = 0; /* allow copy-up */
+		break;
+	case EVM_XATTR_HMAC:
+	case EVM_IMA_XATTR_DIGSIG:
+	default:
+		rc = 1; /* discard */
+	}
+
+	kfree(xattr_data);
+	return rc;
 }
 
 /*
-- 
2.43.0