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evm: posix acls modify i_mode

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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>
This commit is contained in:
Mimi Zohar 2011-08-18 18:07:44 -04:00
parent a924ce0b35
commit bf6d0f5dcd
5 changed files with 59 additions and 5 deletions
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8
include/linux/evm.h
View file

@ -33,6 +33,14 @@ extern void evm_inode_post_removexattr(struct dentry *dentry,
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,

5
include/linux/xattr.h
View file

@ -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>

1
security/integrity/evm/Makefile
View file

@ -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

24
security/integrity/evm/evm_main.c
View file

@ -177,7 +177,14 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
/*
* 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 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
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 @@ int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
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);

26
security/integrity/evm/evm_posix_acl.c Normal file
View file

@ -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;
}