evm: posix acls modify i_mode
The posix xattr acls are 'system' prefixed, which normally would not
affect security.evm. An interesting side affect of writing posix xattr
acls is their modifying of the i_mode, which is included in security.evm.
This patch updates security.evm when posix xattr acls are written.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
diff --git a/include/linux/evm.h b/include/linux/evm.h
index ea603c9..9fc13a7 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -33,6 +33,14 @@
extern int evm_inode_init_security(struct inode *inode,
const struct xattr *xattr_array,
struct xattr *evm);
+#ifdef CONFIG_FS_POSIX_ACL
+extern int posix_xattr_acl(const char *xattrname);
+#else
+static inline int posix_xattr_acl(const char *xattrname)
+{
+ return 0;
+}
+#endif
#else
#ifdef CONFIG_INTEGRITY
static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index b20cb96..e5d1220 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -52,6 +52,11 @@
#define XATTR_CAPS_SUFFIX "capability"
#define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX
+#define XATTR_POSIX_ACL_ACCESS "posix_acl_access"
+#define XATTR_NAME_POSIX_ACL_ACCESS XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_ACCESS
+#define XATTR_POSIX_ACL_DEFAULT "posix_acl_default"
+#define XATTR_NAME_POSIX_ACL_DEFAULT XATTR_SYSTEM_PREFIX XATTR_POSIX_ACL_DEFAULT
+
#ifdef __KERNEL__
#include <linux/types.h>
diff --git a/security/integrity/evm/Makefile b/security/integrity/evm/Makefile
index 0787d26..7393c41 100644
--- a/security/integrity/evm/Makefile
+++ b/security/integrity/evm/Makefile
@@ -4,3 +4,4 @@
obj-$(CONFIG_EVM) += evm.o
evm-y := evm_main.o evm_crypto.o evm_secfs.o
+evm-$(CONFIG_FS_POSIX_ACL) += evm_posix_acl.o
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 7d42475..73c008d 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -177,7 +177,14 @@
/*
* evm_protect_xattr - protect the EVM extended attribute
*
- * Prevent security.evm from being modified or removed.
+ * Prevent security.evm from being modified or removed without the
+ * necessary permissions or when the existing value is invalid.
+ *
+ * The posix xattr acls are 'system' prefixed, which normally would not
+ * affect security.evm. An interesting side affect of writing posix xattr
+ * acls is their modifying of the i_mode, which is included in security.evm.
+ * For posix xattr acls only, permit security.evm, even if it currently
+ * doesn't exist, to be updated.
*/
static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
@@ -187,9 +194,15 @@
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
- } else if (!evm_protected_xattr(xattr_name))
- return 0;
-
+ } else if (!evm_protected_xattr(xattr_name)) {
+ if (!posix_xattr_acl(xattr_name))
+ return 0;
+ evm_status = evm_verify_current_integrity(dentry);
+ if ((evm_status == INTEGRITY_PASS) ||
+ (evm_status == INTEGRITY_NOLABEL))
+ return 0;
+ return -EPERM;
+ }
evm_status = evm_verify_current_integrity(dentry);
return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
}
@@ -240,7 +253,8 @@
void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
- if (!evm_initialized || !evm_protected_xattr(xattr_name))
+ if (!evm_initialized || (!evm_protected_xattr(xattr_name)
+ && !posix_xattr_acl(xattr_name)))
return;
evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
diff --git a/security/integrity/evm/evm_posix_acl.c b/security/integrity/evm/evm_posix_acl.c
new file mode 100644
index 0000000..b1753e9
--- /dev/null
+++ b/security/integrity/evm/evm_posix_acl.c
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2011 IBM Corporation
+ *
+ * Author:
+ * Mimi Zohar <zohar@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 2 of the License.
+ */
+
+#include <linux/module.h>
+#include <linux/xattr.h>
+
+int posix_xattr_acl(char *xattr)
+{
+ int xattr_len = strlen(xattr);
+
+ if ((strlen(XATTR_NAME_POSIX_ACL_ACCESS) == xattr_len)
+ && (strncmp(XATTR_NAME_POSIX_ACL_ACCESS, xattr, xattr_len) == 0))
+ return 1;
+ if ((strlen(XATTR_NAME_POSIX_ACL_DEFAULT) == xattr_len)
+ && (strncmp(XATTR_NAME_POSIX_ACL_DEFAULT, xattr, xattr_len) == 0))
+ return 1;
+ return 0;
+}