evm: Move to LSM infrastructure

As for IMA, move hardcoded EVM function calls from various places in the
kernel to the LSM infrastructure, by introducing a new LSM named 'evm'
(last and always enabled like 'ima'). The order in the Makefile ensures
that 'evm' hooks are executed after 'ima' ones.

Make EVM functions as static (except for evm_inode_init_security(), which
is exported), and register them as hook implementations in init_evm_lsm().
Also move the inline functions evm_inode_remove_acl(),
evm_inode_post_remove_acl(), and evm_inode_post_set_acl() from the public
evm.h header to evm_main.c.

Unlike before (see commit to move IMA to the LSM infrastructure),
evm_inode_post_setattr(), evm_inode_post_set_acl(),
evm_inode_post_remove_acl(), and evm_inode_post_removexattr() are not
executed for private inodes.

Finally, add the LSM_ID_EVM case in lsm_list_modules_test.c

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

2 files changed, 112 insertions, 49 deletions

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index d35143179699..0a089af83a45 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -589,9 +589,9 @@ out:
  * 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;
 
@@ -621,8 +621,8 @@ 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
@@ -672,9 +672,11 @@ 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;
 
@@ -713,6 +715,24 @@ 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;
@@ -761,9 +781,11 @@ 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;
@@ -783,6 +805,21 @@ void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
 }
 
 /**
+ * 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
  * @xattr_name: pointer to the affected extended attribute name
@@ -792,7 +829,8 @@ 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;
@@ -808,6 +846,22 @@ 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)
 {
@@ -831,8 +885,8 @@ 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;
@@ -883,8 +937,8 @@ 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;
@@ -901,7 +955,7 @@ void evm_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		evm_update_evmxattr(dentry, NULL, NULL, 0);
 }
 
-int evm_inode_copy_up_xattr(const char *name)
+static int evm_inode_copy_up_xattr(const char *name)
 {
 	if (strcmp(name, XATTR_NAME_EVM) == 0)
 		return 1; /* Discard */
@@ -1004,4 +1058,36 @@ error:
 	return error;
 }
 
+static struct security_hook_list evm_hooks[] __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_copy_up_xattr, evm_inode_copy_up_xattr),
+	LSM_HOOK_INIT(inode_setxattr, evm_inode_setxattr),
+	LSM_HOOK_INIT(inode_post_setxattr, evm_inode_post_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_removexattr, evm_inode_removexattr),
+	LSM_HOOK_INIT(inode_post_removexattr, evm_inode_post_removexattr),
+	LSM_HOOK_INIT(inode_init_security, evm_inode_init_security),
+};
+
+static const struct lsm_id evm_lsmid = {
+	.name = "evm",
+	.id = LSM_ID_EVM,
+};
+
+static int __init init_evm_lsm(void)
+{
+	security_add_hooks(evm_hooks, ARRAY_SIZE(evm_hooks), &evm_lsmid);
+	return 0;
+}
+
+DEFINE_LSM(evm) = {
+	.name = "evm",
+	.init = init_evm_lsm,
+	.order = LSM_ORDER_LAST,
+};
+
 late_initcall(init_evm);
diff --git a/security/security.c b/security/security.c
index bed659b53e59..59cb0e6cbae3 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>
 
@@ -50,7 +50,8 @@
 	(IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM) ? 1 : 0) + \
 	(IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0) + \
 	(IS_ENABLED(CONFIG_SECURITY_LANDLOCK) ? 1 : 0) + \
-	(IS_ENABLED(CONFIG_IMA) ? 1 : 0))
+	(IS_ENABLED(CONFIG_IMA) ? 1 : 0) + \
+	(IS_ENABLED(CONFIG_EVM) ? 1 : 0))
 
 /*
  * These are descriptions of the reasons that can be passed to the
@@ -1740,10 +1741,6 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
 	if (!xattr_count)
 		goto out;
 
-	ret = evm_inode_init_security(inode, dir, qstr, new_xattrs,
-				      &xattr_count);
-	if (ret)
-		goto out;
 	ret = initxattrs(inode, new_xattrs, fs_data);
 out:
 	for (; xattr_count > 0; xattr_count--)
@@ -2235,14 +2232,9 @@ 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);
 
@@ -2307,9 +2299,7 @@ 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;
 }
 
 /**
@@ -2328,15 +2318,10 @@ 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);
 }
 
 /**
@@ -2389,14 +2374,9 @@ 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);
 }
 
 /**
@@ -2432,7 +2412,6 @@ 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);
 }
 
 /**
@@ -2493,9 +2472,7 @@ 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;
 }
 
 /**
@@ -2699,7 +2676,7 @@ int security_inode_copy_up_xattr(const char *name)
 			return rc;
 	}
 
-	return evm_inode_copy_up_xattr(name);
+	return LSM_RET_DEFAULT(inode_copy_up_xattr);
 }
 EXPORT_SYMBOL(security_inode_copy_up_xattr);