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

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On 9/4/23 09:34, Roberto Sassu wrote:
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;
  	}
+

Nit: remove empty line.


+	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


Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>





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