[PATCH v4 17/23] security: Introduce inode_post_remove_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_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 at huawei.com>
Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>
---
 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 42962ce8301a..8ff172ba5681 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 278b97f688dc..d8e359d651d2 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 622c24cbfbb6..6ca8fdd1f037 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2406,6 +2406,23 @@ 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 sec after remove_acl op
+ * @idmap: idmap of the mount
+ * @dentry: file
+ * @acl_name: acl name
+ *
+ * Update inode security field after successful remove_acl operation 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