[PATCH v3 12/25] security: Introduce inode_post_setattr 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_setattr hook.

It is useful for EVM to recalculate the HMAC on modified file attributes
and other file metadata, after it verified the HMAC of current file
metadata with the inode_setattr hook.

LSMs should use the new hook instead of inode_setattr, when they need to
know that the operation was done successfully (not known in inode_setattr).
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>
---
 fs/attr.c                     |  1 +
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/security.h      |  7 +++++++
 security/security.c           | 16 ++++++++++++++++
 4 files changed, 26 insertions(+)

diff --git a/fs/attr.c b/fs/attr.c
index 431f667726c7..3c309eb456c6 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -486,6 +486,7 @@ 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);
 		ima_inode_post_setattr(idmap, dentry, ia_valid);
 		evm_inode_post_setattr(idmap, dentry, ia_valid);
 	}
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index fdf075a6b1bb..995d30336cfa 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -136,6 +136,8 @@ LSM_HOOK(int, 0, inode_follow_link, struct dentry *dentry, struct inode *inode,
 LSM_HOOK(int, 0, inode_permission, struct inode *inode, int mask)
 LSM_HOOK(int, 0, inode_setattr, struct mnt_idmap *idmap, struct dentry *dentry,
 	 struct iattr *attr)
+LSM_HOOK(void, LSM_RET_VOID, inode_post_setattr, struct mnt_idmap *idmap,
+	 struct dentry *dentry, int ia_valid)
 LSM_HOOK(int, 0, inode_getattr, const struct path *path)
 LSM_HOOK(int, 0, inode_setxattr, struct mnt_idmap *idmap,
 	 struct dentry *dentry, const char *name, const void *value,
diff --git a/include/linux/security.h b/include/linux/security.h
index dcb3604ffab8..820899db5276 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -355,6 +355,8 @@ int security_inode_follow_link(struct dentry *dentry, struct inode *inode,
 int security_inode_permission(struct inode *inode, int mask);
 int security_inode_setattr(struct mnt_idmap *idmap,
 			   struct dentry *dentry, struct iattr *attr);
+void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+				 int ia_valid);
 int security_inode_getattr(const struct path *path);
 int security_inode_setxattr(struct mnt_idmap *idmap,
 			    struct dentry *dentry, const char *name,
@@ -856,6 +858,11 @@ static inline int security_inode_setattr(struct mnt_idmap *idmap,
 	return 0;
 }
 
+static inline void
+security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+			    int ia_valid)
+{ }
+
 static inline int security_inode_getattr(const struct path *path)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index 2b24d01cf181..764a6f28b3b9 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2124,6 +2124,22 @@ int security_inode_setattr(struct mnt_idmap *idmap,
 }
 EXPORT_SYMBOL_GPL(security_inode_setattr);
 
+/**
+ * security_inode_post_setattr() - Update the inode after a setattr operation
+ * @idmap: idmap of the mount
+ * @dentry: file
+ * @ia_valid: file attributes set
+ *
+ * Update inode security field after successful setting file attributes.
+ */
+void security_inode_post_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+				 int ia_valid)
+{
+	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+		return;
+	call_void_hook(inode_post_setattr, idmap, dentry, ia_valid);
+}
+
 /**
  * security_inode_getattr() - Check if getting file attributes is allowed
  * @path: file
-- 
2.34.1