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

Stefan Berger
2023-09-05T18:49:55Z

On 9/4/23 09:34, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> 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@huawei.com>
> ---
> 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@linux.ibm.com>