[PATCH v5 17/23] security: Introduce inode_post_remove_acl hook

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

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

At inode_remove_acl hook, EVM verifies the file's existing HMAC value. At
inode_post_remove_acl, EVM re-calculates the file's HMAC with the passed
POSIX ACL removed and other file metadata.

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

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

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
 fs/posix_acl.c                |  1 +
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/security.h      |  8 ++++++++
 security/security.c           | 17 +++++++++++++++++
 4 files changed, 28 insertions(+)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 58e3c1e2fbbc..e3fbe1a9f3f5 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -1246,6 +1246,7 @@ int vfs_remove_acl(struct mnt_idmap *idmap, struct dentry *dentry,
 		error = -EIO;
 	if (!error) {
 		fsnotify_xattr(dentry);
+		security_inode_post_remove_acl(idmap, dentry, acl_name);
 		evm_inode_post_remove_acl(idmap, dentry, acl_name);
 	}
 
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 6a671616196f..2bf128f7cbae 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -163,6 +163,8 @@ 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,
 	 struct dentry *dentry, const char *acl_name)
+LSM_HOOK(void, LSM_RET_VOID, inode_post_remove_acl, struct mnt_idmap *idmap,
+	 struct dentry *dentry, const char *acl_name)
 LSM_HOOK(int, 0, inode_need_killpriv, struct dentry *dentry)
 LSM_HOOK(int, 0, inode_killpriv, struct mnt_idmap *idmap,
 	 struct dentry *dentry)
diff --git a/include/linux/security.h b/include/linux/security.h
index d71d0b08e9fe..7cd7126f6545 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -378,6 +378,9 @@ 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,
 			      struct dentry *dentry, const char *acl_name);
+void security_inode_post_remove_acl(struct mnt_idmap *idmap,
+				    struct dentry *dentry,
+				    const char *acl_name);
 void security_inode_post_setxattr(struct dentry *dentry, const char *name,
 				  const void *value, size_t size, int flags);
 int security_inode_getxattr(struct dentry *dentry, const char *name);
@@ -934,6 +937,11 @@ static inline int security_inode_remove_acl(struct mnt_idmap *idmap,
 	return 0;
 }
 
+static inline void security_inode_post_remove_acl(struct mnt_idmap *idmap,
+						  struct dentry *dentry,
+						  const char *acl_name)
+{ }
+
 static inline void security_inode_post_setxattr(struct dentry *dentry,
 		const char *name, const void *value, size_t size, int flags)
 { }
diff --git a/security/security.c b/security/security.c
index d2dbea54a63a..6eb7c9cff1e5 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2413,6 +2413,23 @@ int security_inode_remove_acl(struct mnt_idmap *idmap,
 	return evm_inode_remove_acl(idmap, dentry, acl_name);
 }
 
+/**
+ * security_inode_post_remove_acl() - Update inode security after rm posix acls
+ * @idmap: idmap of the mount
+ * @dentry: file
+ * @acl_name: acl name
+ *
+ * Update inode security data after successfully removing posix acls on
+ * @dentry in @idmap. The posix acls are identified by @acl_name.
+ */
+void security_inode_post_remove_acl(struct mnt_idmap *idmap,
+				    struct dentry *dentry, const char *acl_name)
+{
+	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+		return;
+	call_void_hook(inode_post_remove_acl, idmap, dentry, acl_name);
+}
+
 /**
  * security_inode_post_setxattr() - Update the inode after a setxattr operation
  * @dentry: file
-- 
2.34.1