[PATCH v6 4/5] samples/landlock: Extend sample tool to support LANDLOCK_ACCESS_FS_TRUNCATE

[Mickaël Salaün]

On 08/09/2022 21:58, Günther Noack wrote:
> Update the sandboxer sample to restrict truncate actions. This is
> automatically enabled by default if the running kernel supports
> LANDLOCK_ACCESS_FS_TRUNCATE, expect for the paths listed in the

except for

> LL_FS_RW environment variable.
> 
> Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
> ---
>   samples/landlock/sandboxer.c | 23 ++++++++++++++---------
>   1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index 3e404e51ec64..771b6b10d519 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -76,7 +76,8 @@ static int parse_path(char *env_path, const char ***const path_list)
>   #define ACCESS_FILE ( \
>   	LANDLOCK_ACCESS_FS_EXECUTE | \
>   	LANDLOCK_ACCESS_FS_WRITE_FILE | \
> -	LANDLOCK_ACCESS_FS_READ_FILE)
> +	LANDLOCK_ACCESS_FS_READ_FILE | \
> +	LANDLOCK_ACCESS_FS_TRUNCATE)
>   
>   /* clang-format on */
>   
> @@ -160,10 +161,8 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
>   	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
>   	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
>   	LANDLOCK_ACCESS_FS_MAKE_SYM | \
> -	LANDLOCK_ACCESS_FS_REFER)
> -
> -#define ACCESS_ABI_2 ( \
> -	LANDLOCK_ACCESS_FS_REFER)
> +	LANDLOCK_ACCESS_FS_REFER | \
> +	LANDLOCK_ACCESS_FS_TRUNCATE)
>   
>   /* clang-format on */
>   
> @@ -226,11 +225,17 @@ int main(const int argc, char *const argv[], char *const *const envp)
>   		return 1;
>   	}
>   	/* Best-effort security. */
> -	if (abi < 2) {
> -		ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2;
> -		access_fs_ro &= ~ACCESS_ABI_2;
> -		access_fs_rw &= ~ACCESS_ABI_2;
> +	switch (abi) {
> +	case 1:
> +		/* Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 */
> +		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
> +		__attribute__((fallthrough));
> +	case 2:
> +		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
> +		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
>   	}
> +	access_fs_ro &= ruleset_attr.handled_access_fs;
> +	access_fs_rw &= ruleset_attr.handled_access_fs;
>   
>   	ruleset_fd =
>   		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);