[PATCH v8 16/24] security: Introduce inode_post_set_acl hook

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu at huawei.com>

In preparation for moving IMA and EVM to the LSM infrastructure, introduce
the inode_post_set_acl hook.

At inode_set_acl hook, EVM verifies the file's existing HMAC value. At
inode_post_set_acl, EVM re-calculates the file's HMAC based on the modified
POSIX ACL and other file metadata.

Other LSMs could similarly take some action after successful POSIX ACL
change.

The new hook cannot return an error and cannot cause the operation to be
reverted.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>
Acked-by: Casey Schaufler <casey at schaufler-ca.com>
Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
---
 fs/posix_acl.c                |  1 +
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/security.h      |  7 +++++++
 security/security.c           | 17 +++++++++++++++++
 4 files changed, 27 insertions(+)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index a05fe94970ce..58e3c1e2fbbc 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -1137,6 +1137,7 @@ int vfs_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
 		error = -EIO;
 	if (!error) {
 		fsnotify_xattr(dentry);
+		security_inode_post_set_acl(dentry, acl_name, kacl);
 		evm_inode_post_set_acl(dentry, acl_name, kacl);
 	}
 
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 4b195996f848..5133dd88b5fb 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -157,6 +157,8 @@ LSM_HOOK(void, LSM_RET_VOID, inode_post_removexattr, struct dentry *dentry,
 	 const char *name)
 LSM_HOOK(int, 0, inode_set_acl, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *acl_name, struct posix_acl *kacl)
+LSM_HOOK(void, LSM_RET_VOID, inode_post_set_acl, struct dentry *dentry,
+	 const char *acl_name, struct posix_acl *kacl)
 LSM_HOOK(int, 0, inode_get_acl, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *acl_name)
 LSM_HOOK(int, 0, inode_remove_acl, struct mnt_idmap *idmap,
diff --git a/include/linux/security.h b/include/linux/security.h
index d77b717b5a45..948aaddf0edd 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -372,6 +372,8 @@ int security_inode_setxattr(struct mnt_idmap *idmap,
 int security_inode_set_acl(struct mnt_idmap *idmap,
 			   struct dentry *dentry, const char *acl_name,
 			   struct posix_acl *kacl);
+void security_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
+				 struct posix_acl *kacl);
 int security_inode_get_acl(struct mnt_idmap *idmap,
 			   struct dentry *dentry, const char *acl_name);
 int security_inode_remove_acl(struct mnt_idmap *idmap,
@@ -913,6 +915,11 @@ static inline int security_inode_set_acl(struct mnt_idmap *idmap,
 	return 0;
 }
 
+static inline void security_inode_post_set_acl(struct dentry *dentry,
+					       const char *acl_name,
+					       struct posix_acl *kacl)
+{ }
+
 static inline int security_inode_get_acl(struct mnt_idmap *idmap,
 					 struct dentry *dentry,
 					 const char *acl_name)
diff --git a/security/security.c b/security/security.c
index a1bdf4859448..5d25bbd18d66 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2350,6 +2350,23 @@ int security_inode_set_acl(struct mnt_idmap *idmap,
 	return evm_inode_set_acl(idmap, dentry, acl_name, kacl);
 }
 
+/**
+ * security_inode_post_set_acl() - Update inode security from posix acls set
+ * @dentry: file
+ * @acl_name: acl name
+ * @kacl: acl struct
+ *
+ * Update inode security data after successfully setting posix acls on @dentry.
+ * The posix acls in @kacl are identified by @acl_name.
+ */
+void security_inode_post_set_acl(struct dentry *dentry, const char *acl_name,
+				 struct posix_acl *kacl)
+{
+	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+		return;
+	call_void_hook(inode_post_set_acl, dentry, acl_name, kacl);
+}
+
 /**
  * security_inode_get_acl() - Check if reading posix acls is allowed
  * @idmap: idmap of the mount
-- 
2.34.1