[PATCH v5 14/23] security: Introduce path_post_mknod hook

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

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

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

IMA-appraisal requires all existing files in policy to have a file
hash/signature stored in security.ima. An exception is made for empty files
created by mknod, by tagging them as new files.

LSMs could also take some action after files are created.

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

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 fs/namei.c                    |  5 +++++
 include/linux/lsm_hook_defs.h |  2 ++
 include/linux/security.h      |  5 +++++
 security/security.c           | 14 ++++++++++++++
 4 files changed, 26 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index fb93d3e13df6..b7f433720b1e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4047,6 +4047,11 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 					  dentry, mode, 0);
 			break;
 	}
+
+	if (error)
+		goto out2;
+
+	security_path_post_mknod(idmap, dentry);
 out2:
 	done_path_create(&path, dentry);
 	if (retry_estale(error, lookup_flags)) {
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 5d0a09ead7ac..e491951399f7 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -94,6 +94,8 @@ LSM_HOOK(int, 0, path_mkdir, const struct path *dir, struct dentry *dentry,
 LSM_HOOK(int, 0, path_rmdir, const struct path *dir, struct dentry *dentry)
 LSM_HOOK(int, 0, path_mknod, const struct path *dir, struct dentry *dentry,
 	 umode_t mode, unsigned int dev)
+LSM_HOOK(void, LSM_RET_VOID, path_post_mknod, struct mnt_idmap *idmap,
+	 struct dentry *dentry)
 LSM_HOOK(int, 0, path_truncate, const struct path *path)
 LSM_HOOK(int, 0, path_symlink, const struct path *dir, struct dentry *dentry,
 	 const char *old_name)
diff --git a/include/linux/security.h b/include/linux/security.h
index a570213693d9..68cbdc84506e 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1884,6 +1884,7 @@ int security_path_mkdir(const struct path *dir, struct dentry *dentry, umode_t m
 int security_path_rmdir(const struct path *dir, struct dentry *dentry);
 int security_path_mknod(const struct path *dir, struct dentry *dentry, umode_t mode,
 			unsigned int dev);
+void security_path_post_mknod(struct mnt_idmap *idmap, struct dentry *dentry);
 int security_path_truncate(const struct path *path);
 int security_path_symlink(const struct path *dir, struct dentry *dentry,
 			  const char *old_name);
@@ -1918,6 +1919,10 @@ static inline int security_path_mknod(const struct path *dir, struct dentry *den
 	return 0;
 }
 
+static inline void security_path_post_mknod(struct mnt_idmap *idmap,
+					    struct dentry *dentry)
+{ }
+
 static inline int security_path_truncate(const struct path *path)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index 331a3e5efb62..5eaf5f2aa5ea 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1800,6 +1800,20 @@ int security_path_mknod(const struct path *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL(security_path_mknod);
 
+/**
+ * security_path_post_mknod() - Update inode security field after file creation
+ * @idmap: idmap of the mount
+ * @dentry: new file
+ *
+ * Update inode security field after a file has been created.
+ */
+void security_path_post_mknod(struct mnt_idmap *idmap, struct dentry *dentry)
+{
+	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
+		return;
+	call_void_hook(path_post_mknod, idmap, dentry);
+}
+
 /**
  * security_path_mkdir() - Check if creating a new directory is allowed
  * @dir: parent directory
-- 
2.34.1