[PATCH 26/28] evm: Move to LSM infrastructure

From: Roberto Sassu
Date: Fri Mar 03 2023 - 13:28:51 EST

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

As for IMA, remove hardcoded EVM function calls from the LSM infrastructure
and the VFS. Make EVM functions as static (except for
evm_inode_init_security(), which is exported), and register them as hook
implementations in init_evm_lsm(), called from integrity_lsm_init().

Finally, switch to the LSM reservation mechanism for the EVM xattr, by
setting the lbs_xattr field of the lsm_blob_sizes structure, and
consequently decrement the number of xattrs to allocate in
security_inode_init_security().

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
fs/attr.c | 2 -
fs/posix_acl.c | 3 -
fs/xattr.c | 2 -
include/linux/evm.h | 116 ------------------------------
security/integrity/evm/evm_main.c | 106 ++++++++++++++++++++++-----
security/integrity/iint.c | 7 ++
security/integrity/integrity.h | 9 +++
security/security.c | 41 +++--------
8 files changed, 115 insertions(+), 171 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 406d782dfab..1b911a627fe 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -16,7 +16,6 @@
#include <linux/fcntl.h>
#include <linux/filelock.h>
#include <linux/security.h>
-#include <linux/evm.h>

#include "internal.h"

@@ -485,7 +484,6 @@ int notify_change(struct mnt_idmap *idmap, struct dentry *dentry,
if (!error) {
fsnotify_change(dentry, ia_valid);
security_inode_post_setattr(idmap, dentry, ia_valid);
- evm_inode_post_setattr(idmap, dentry, ia_valid);
}

return error;
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 5b8c92fce0c..608cb0a9f84 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -26,7 +26,6 @@
#include <linux/mnt_idmapping.h>
#include <linux/iversion.h>
#include <linux/security.h>
-#include <linux/evm.h>
#include <linux/fsnotify.h>
#include <linux/filelock.h>

@@ -1103,7 +1102,6 @@ int vfs_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_set_acl(dentry, acl_name, kacl);
- evm_inode_post_set_acl(dentry, acl_name, kacl);
}

out_inode_unlock:
@@ -1214,7 +1212,6 @@ int vfs_remove_acl(struct mnt_idmap *idmap, struct dentry *dentry,
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_remove_acl(idmap, dentry, acl_name);
- evm_inode_post_remove_acl(idmap, dentry, acl_name);
}

out_inode_unlock:
diff --git a/fs/xattr.c b/fs/xattr.c
index 10c959d9fc6..7708ffdacca 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -16,7 +16,6 @@
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/security.h>
-#include <linux/evm.h>
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/fsnotify.h>
@@ -535,7 +534,6 @@ __vfs_removexattr_locked(struct mnt_idmap *idmap,
if (!error) {
fsnotify_xattr(dentry);
security_inode_post_removexattr(dentry, name);
- evm_inode_post_removexattr(dentry, name);
}

out:
diff --git a/include/linux/evm.h b/include/linux/evm.h
index 8c043273552..61794299f09 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -21,46 +21,6 @@ extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
void *xattr_value,
size_t xattr_value_len,
struct integrity_iint_cache *iint);
-extern int evm_inode_setattr(struct mnt_idmap *idmap,
- struct dentry *dentry, struct iattr *attr);
-extern void evm_inode_post_setattr(struct mnt_idmap *idmap,
- struct dentry *dentry, int ia_valid);
-extern int evm_inode_setxattr(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *name,
- const void *value, size_t size, int flags);
-extern void evm_inode_post_setxattr(struct dentry *dentry,
- const char *xattr_name,
- const void *xattr_value,
- size_t xattr_value_len,
- int flags);
-extern int evm_inode_removexattr(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *xattr_name);
-extern void evm_inode_post_removexattr(struct dentry *dentry,
- const char *xattr_name);
-static inline void evm_inode_post_remove_acl(struct mnt_idmap *idmap,
- struct dentry *dentry,
- const char *acl_name)
-{
- evm_inode_post_removexattr(dentry, acl_name);
-}
-extern int evm_inode_set_acl(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *acl_name,
- struct posix_acl *kacl);
-static inline int evm_inode_remove_acl(struct mnt_idmap *idmap,
- struct dentry *dentry,
- const char *acl_name)
-{
- return evm_inode_set_acl(idmap, dentry, acl_name, NULL);
-}
-static inline void evm_inode_post_set_acl(struct dentry *dentry,
- const char *acl_name,
- struct posix_acl *kacl)
-{
- return evm_inode_post_setxattr(dentry, acl_name, NULL, 0, 0);
-}
-extern int evm_inode_init_security(struct inode *inode, struct inode *dir,
- const struct qstr *qstr,
- struct xattr *xattrs);
extern bool evm_revalidate_status(const char *xattr_name);
extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
@@ -92,82 +52,6 @@ static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
}
#endif

-static inline int evm_inode_setattr(struct mnt_idmap *idmap,
- struct dentry *dentry, struct iattr *attr)
-{
- return 0;
-}
-
-static inline void evm_inode_post_setattr(struct mnt_idmap *idmap,
- struct dentry *dentry, int ia_valid)
-{
- return;
-}
-
-static inline int evm_inode_setxattr(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *name,
- const void *value, size_t size, int flags)
-{
- return 0;
-}
-
-static inline void evm_inode_post_setxattr(struct dentry *dentry,
- const char *xattr_name,
- const void *xattr_value,
- size_t xattr_value_len,
- int flags)
-{
- return;
-}
-
-static inline int evm_inode_removexattr(struct mnt_idmap *idmap,
- struct dentry *dentry,
- const char *xattr_name)
-{
- return 0;
-}
-
-static inline void evm_inode_post_removexattr(struct dentry *dentry,
- const char *xattr_name)
-{
- return;
-}
-
-static inline void evm_inode_post_remove_acl(struct mnt_idmap *idmap,
- struct dentry *dentry,
- const char *acl_name)
-{
- return;
-}
-
-static inline int evm_inode_set_acl(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *acl_name,
- struct posix_acl *kacl)
-{
- return 0;
-}
-
-static inline int evm_inode_remove_acl(struct mnt_idmap *idmap,
- struct dentry *dentry,
- const char *acl_name)
-{
- return 0;
-}
-
-static inline void evm_inode_post_set_acl(struct dentry *dentry,
- const char *acl_name,
- struct posix_acl *kacl)
-{
- return;
-}
-
-static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
- const struct qstr *qstr,
- struct xattr *xattrs)
-{
- return 0;
-}
-
static inline bool evm_revalidate_status(const char *xattr_name)
{
return false;
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 8b5c472f78b..c45bc97277c 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -19,6 +19,7 @@
#include <linux/xattr.h>
#include <linux/integrity.h>
#include <linux/evm.h>
+#include <linux/lsm_hooks.h>
#include <linux/magic.h>
#include <linux/posix_acl_xattr.h>

@@ -566,9 +567,9 @@ static int evm_protect_xattr(struct mnt_idmap *idmap,
* userspace from writing HMAC value. Writing 'security.evm' requires
* requires CAP_SYS_ADMIN privileges.
*/
-int evm_inode_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
- const char *xattr_name, const void *xattr_value,
- size_t xattr_value_len, int flags)
+static int evm_inode_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
+ const char *xattr_name, const void *xattr_value,
+ size_t xattr_value_len, int flags)
{
const struct evm_ima_xattr_data *xattr_data = xattr_value;

@@ -598,8 +599,8 @@ int evm_inode_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
* Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
* the current value is valid.
*/
-int evm_inode_removexattr(struct mnt_idmap *idmap,
- struct dentry *dentry, const char *xattr_name)
+static int evm_inode_removexattr(struct mnt_idmap *idmap, struct dentry *dentry,
+ const char *xattr_name)
{
/* Policy permits modification of the protected xattrs even though
* there's no HMAC key loaded
@@ -649,9 +650,11 @@ static inline int evm_inode_set_acl_change(struct mnt_idmap *idmap,
* Prevent modifying posix acls causing the EVM HMAC to be re-calculated
* and 'security.evm' xattr updated, unless the existing 'security.evm' is
* valid.
+ *
+ * Return: zero on success, -EPERM on failure.
*/
-int evm_inode_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
- const char *acl_name, struct posix_acl *kacl)
+static int evm_inode_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
+ const char *acl_name, struct posix_acl *kacl)
{
enum integrity_status evm_status;

@@ -690,6 +693,24 @@ int evm_inode_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
return -EPERM;
}

+/**
+ * evm_inode_remove_acl - Protect the EVM extended attribute from posix acls
+ * @idmap: idmap of the mount
+ * @dentry: pointer to the affected dentry
+ * @acl_name: name of the posix acl
+ *
+ * Prevent removing posix acls causing the EVM HMAC to be re-calculated
+ * and 'security.evm' xattr updated, unless the existing 'security.evm' is
+ * valid.
+ *
+ * Return: zero on success, -EPERM on failure.
+ */
+static int evm_inode_remove_acl(struct mnt_idmap *idmap, struct dentry *dentry,
+ const char *acl_name)
+{
+ return evm_inode_set_acl(idmap, dentry, acl_name, NULL);
+}
+
static void evm_reset_status(struct inode *inode)
{
struct integrity_iint_cache *iint;
@@ -738,9 +759,11 @@ bool evm_revalidate_status(const char *xattr_name)
* __vfs_setxattr_noperm(). The caller of which has taken the inode's
* i_mutex lock.
*/
-void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
- const void *xattr_value, size_t xattr_value_len,
- int flags)
+static void evm_inode_post_setxattr(struct dentry *dentry,
+ const char *xattr_name,
+ const void *xattr_value,
+ size_t xattr_value_len,
+ int flags)
{
if (!evm_revalidate_status(xattr_name))
return;
@@ -756,6 +779,21 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
}

+/**
+ * evm_inode_post_set_acl - Update the EVM extended attribute from posix acls
+ * @dentry: pointer to the affected dentry
+ * @acl_name: name of the posix acl
+ * @kacl: pointer to the posix acls
+ *
+ * Update the 'security.evm' xattr with the EVM HMAC re-calculated after setting
+ * posix acls.
+ */
+static void evm_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
+ struct posix_acl *kacl)
+{
+ return evm_inode_post_setxattr(dentry, acl_name, NULL, 0, 0);
+}
+
/**
* evm_inode_post_removexattr - update 'security.evm' after removing the xattr
* @dentry: pointer to the affected dentry
@@ -766,7 +804,8 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
* No need to take the i_mutex lock here, as this function is called from
* vfs_removexattr() which takes the i_mutex.
*/
-void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
+static void evm_inode_post_removexattr(struct dentry *dentry,
+ const char *xattr_name)
{
if (!evm_revalidate_status(xattr_name))
return;
@@ -782,6 +821,22 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
evm_update_evmxattr(dentry, xattr_name, NULL, 0);
}

+/**
+ * evm_inode_post_remove_acl - Update the EVM extended attribute from posix acls
+ * @idmap: idmap of the mount
+ * @dentry: pointer to the affected dentry
+ * @acl_name: name of the posix acl
+ *
+ * Update the 'security.evm' xattr with the EVM HMAC re-calculated after
+ * removing posix acls.
+ */
+static inline void evm_inode_post_remove_acl(struct mnt_idmap *idmap,
+ struct dentry *dentry,
+ const char *acl_name)
+{
+ evm_inode_post_removexattr(dentry, acl_name);
+}
+
static int evm_attr_change(struct mnt_idmap *idmap,
struct dentry *dentry, struct iattr *attr)
{
@@ -805,8 +860,8 @@ static int evm_attr_change(struct mnt_idmap *idmap,
* Permit update of file attributes when files have a valid EVM signature,
* except in the case of them having an immutable portable signature.
*/
-int evm_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
- struct iattr *attr)
+static int evm_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+ struct iattr *attr)
{
unsigned int ia_valid = attr->ia_valid;
enum integrity_status evm_status;
@@ -853,8 +908,8 @@ int evm_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
* This function is called from notify_change(), which expects the caller
* to lock the inode's i_mutex.
*/
-void evm_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
- int ia_valid)
+static void evm_inode_post_setattr(struct mnt_idmap *idmap,
+ struct dentry *dentry, int ia_valid)
{
if (!evm_revalidate_status(NULL))
return;
@@ -892,7 +947,7 @@ int evm_inode_init_security(struct inode *inode, struct inode *dir,
if (!evm_protected_xattrs)
return -EOPNOTSUPP;

- evm_xattr = xattr;
+ evm_xattr = xattrs + integrity_blob_sizes.lbs_xattr;

xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
if (!xattr_data)
@@ -952,4 +1007,23 @@ static int __init init_evm(void)
return error;
}

+static struct security_hook_list evm_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(inode_setattr, evm_inode_setattr),
+ LSM_HOOK_INIT(inode_post_setattr, evm_inode_post_setattr),
+ LSM_HOOK_INIT(inode_setxattr, evm_inode_setxattr),
+ LSM_HOOK_INIT(inode_set_acl, evm_inode_set_acl),
+ LSM_HOOK_INIT(inode_post_set_acl, evm_inode_post_set_acl),
+ LSM_HOOK_INIT(inode_remove_acl, evm_inode_remove_acl),
+ LSM_HOOK_INIT(inode_post_remove_acl, evm_inode_post_remove_acl),
+ LSM_HOOK_INIT(inode_post_setxattr, evm_inode_post_setxattr),
+ LSM_HOOK_INIT(inode_removexattr, evm_inode_removexattr),
+ LSM_HOOK_INIT(inode_post_removexattr, evm_inode_post_removexattr),
+ LSM_HOOK_INIT(inode_init_security, evm_inode_init_security),
+};
+
+void __init init_evm_lsm(void)
+{
+ security_add_hooks(evm_hooks, ARRAY_SIZE(evm_hooks), "integrity");
+}
+
late_initcall(init_evm);
diff --git a/security/integrity/iint.c b/security/integrity/iint.c
index bbadf974b31..952d5ea4e18 100644
--- a/security/integrity/iint.c
+++ b/security/integrity/iint.c
@@ -179,12 +179,19 @@ static int __init integrity_lsm_init(void)
0, SLAB_PANIC, init_once);

init_ima_lsm();
+ init_evm_lsm();
return 0;
}
+
+struct lsm_blob_sizes integrity_blob_sizes __lsm_ro_after_init = {
+ .lbs_xattr = 1,
+};
+
DEFINE_LSM(integrity) = {
.name = "integrity",
.init = integrity_lsm_init,
.order = LSM_ORDER_LAST,
+ .blobs = &integrity_blob_sizes,
};

/*
diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
index c72d375a356..76e7eda6651 100644
--- a/security/integrity/integrity.h
+++ b/security/integrity/integrity.h
@@ -188,6 +188,7 @@ int integrity_kernel_read(struct file *file, loff_t offset,
#define INTEGRITY_KEYRING_MAX 4

extern struct dentry *integrity_dir;
+extern struct lsm_blob_sizes integrity_blob_sizes;

struct modsig;

@@ -199,6 +200,14 @@ static inline void __init init_ima_lsm(void)
}
#endif

+#ifdef CONFIG_EVM
+void __init init_evm_lsm(void);
+#else
+static inline void __init init_evm_lsm(void)
+{
+}
+#endif
+
#ifdef CONFIG_INTEGRITY_SIGNATURE

int integrity_digsig_verify(const unsigned int id, const char *sig, int siglen,
diff --git a/security/security.c b/security/security.c
index 9bc6a4ef758..74abf04feef 100644
--- a/security/security.c
+++ b/security/security.c
@@ -20,13 +20,13 @@
#include <linux/kernel_read_file.h>
#include <linux/lsm_hooks.h>
#include <linux/integrity.h>
-#include <linux/evm.h>
#include <linux/fsnotify.h>
#include <linux/mman.h>
#include <linux/mount.h>
#include <linux/personality.h>
#include <linux/backing-dev.h>
#include <linux/string.h>
+#include <linux/xattr.h>
#include <linux/msg.h>
#include <net/flow.h>

@@ -1662,8 +1662,8 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
if (!initxattrs)
return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
dir, qstr, NULL);
- /* Allocate +1 for EVM and +1 as terminator. */
- new_xattrs = kcalloc(blob_sizes.lbs_xattr + 2, sizeof(*new_xattrs),
+ /* Allocate +1 for terminator. */
+ new_xattrs = kcalloc(blob_sizes.lbs_xattr + 1, sizeof(*new_xattrs),
GFP_NOFS);
if (!new_xattrs)
return -ENOMEM;
@@ -1699,9 +1699,6 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
if (!num_filled_xattrs)
goto out;

- ret = evm_inode_init_security(inode, dir, qstr, new_xattrs);
- if (ret && ret != -EOPNOTSUPP)
- goto out;
ret = initxattrs(inode, new_xattrs, fs_data);
out:
for (xattr = new_xattrs; xattr->value != NULL; xattr++)
@@ -2201,14 +2198,9 @@ int security_inode_permission(struct inode *inode, int mask)
int security_inode_setattr(struct mnt_idmap *idmap,
struct dentry *dentry, struct iattr *attr)
{
- int ret;
-
if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
return 0;
- ret = call_int_hook(inode_setattr, 0, idmap, dentry, attr);
- if (ret)
- return ret;
- return evm_inode_setattr(idmap, dentry, attr);
+ return call_int_hook(inode_setattr, 0, idmap, dentry, attr);
}
EXPORT_SYMBOL_GPL(security_inode_setattr);

@@ -2272,9 +2264,7 @@ int security_inode_setxattr(struct mnt_idmap *idmap,

if (ret == 1)
ret = cap_inode_setxattr(dentry, name, value, size, flags);
- if (ret)
- return ret;
- return evm_inode_setxattr(idmap, dentry, name, value, size, flags);
+ return ret;
}

/**
@@ -2293,15 +2283,10 @@ int security_inode_set_acl(struct mnt_idmap *idmap,
struct dentry *dentry, const char *acl_name,
struct posix_acl *kacl)
{
- int ret;
-
if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
return 0;
- ret = call_int_hook(inode_set_acl, 0, idmap, dentry, acl_name,
- kacl);
- if (ret)
- return ret;
- return evm_inode_set_acl(idmap, dentry, acl_name, kacl);
+ return call_int_hook(inode_set_acl, 0, idmap, dentry, acl_name,
+ kacl);
}

/**
@@ -2354,14 +2339,9 @@ int security_inode_get_acl(struct mnt_idmap *idmap,
int security_inode_remove_acl(struct mnt_idmap *idmap,
struct dentry *dentry, const char *acl_name)
{
- int ret;
-
if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
return 0;
- ret = call_int_hook(inode_remove_acl, 0, idmap, dentry, acl_name);
- if (ret)
- return ret;
- return evm_inode_remove_acl(idmap, dentry, acl_name);
+ return call_int_hook(inode_remove_acl, 0, idmap, dentry, acl_name);
}

/**
@@ -2397,7 +2377,6 @@ void security_inode_post_setxattr(struct dentry *dentry, const char *name,
if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
return;
call_void_hook(inode_post_setxattr, dentry, name, value, size, flags);
- evm_inode_post_setxattr(dentry, name, value, size, flags);
}

/**
@@ -2458,9 +2437,7 @@ int security_inode_removexattr(struct mnt_idmap *idmap,
ret = call_int_hook(inode_removexattr, 1, idmap, dentry, name);
if (ret == 1)
ret = cap_inode_removexattr(idmap, dentry, name);
- if (ret)
- return ret;
- return evm_inode_removexattr(idmap, dentry, name);
+ return ret;
}

/**
--
2.25.1