[PATCH v3 16/25] security: Introduce path_post_mknod hook

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

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

It is useful for IMA to let new empty files be subsequently opened for
further modification.

LSMs can benefit from this hook to update the inode state after a file has
been successfully created. The new hook cannot return an error and cannot
cause the operation to be canceled.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
 fs/namei.c                    |  5 +++++
 include/linux/lsm_hook_defs.h |  3 +++
 include/linux/security.h      |  9 +++++++++
 security/security.c           | 19 +++++++++++++++++++
 4 files changed, 36 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 7dc4626859f0..c8c4ab26b52a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4061,6 +4061,11 @@ 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, &path, dentry, mode_stripped, dev);
 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 797f51da3f7d..b1634b5de98c 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -93,6 +93,9 @@ 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,
+	 const struct path *dir, struct dentry *dentry, umode_t mode,
+	 unsigned int dev)
 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 7871009d59ae..f210bd66e939 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1842,6 +1842,9 @@ 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, const struct path *dir,
+			      struct dentry *dentry, umode_t mode,
+			      unsigned int dev);
 int security_path_truncate(const struct path *path);
 int security_path_symlink(const struct path *dir, struct dentry *dentry,
 			  const char *old_name);
@@ -1876,6 +1879,12 @@ 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,
+					    const struct path *dir,
+					    struct dentry *dentry, umode_t mode,
+					    unsigned int dev)
+{ }
+
 static inline int security_path_truncate(const struct path *path)
 {
 	return 0;
diff --git a/security/security.c b/security/security.c
index fbb58eeeea02..78aeb24efedb 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1702,6 +1702,25 @@ 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
+ * @dir: parent directory
+ * @dentry: new file
+ * @mode: new file mode
+ * @dev: device number
+ *
+ * Update inode security field after a file has been created.
+ */
+void security_path_post_mknod(struct mnt_idmap *idmap, const struct path *dir,
+			      struct dentry *dentry, umode_t mode,
+			      unsigned int dev)
+{
+	if (unlikely(IS_PRIVATE(d_backing_inode(dir->dentry))))
+		return;
+	call_void_hook(path_post_mknod, idmap, dir, dentry, mode, dev);
+}
+
 /**
  * security_path_mkdir() - Check if creating a new directory is allowed
  * @dir: parent directory
-- 
2.34.1