Re: [PATCH v9 14/25] security: Introduce path_post_mknod hook

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

On 1/15/24 13:17, 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.
>
> 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@xxxxxxxxxx>
> Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> ---
>   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 229f84ce12ae..e08b9091350d 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 2997348afcb7..977dd9f7f51a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -1893,6 +1893,7 @@ 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);
> @@ -1927,6 +1928,10 @@ 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 7d10724872f8..750bfe2768d5 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