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SubjectRe: [PATCH net-next v7 08/10] bpf: Add a Landlock sandbox example
On Mon, Aug 21, 2017 at 02:09:31AM +0200, Mickaël Salaün wrote:
> Add a basic sandbox tool to create a process isolated from some part of
> the system. This sandbox create a read-only environment. It is only
> allowed to write to a character device such as a TTY:
>
> # :> X
> # echo $?
> 0
> # ./samples/bpf/landlock1 /bin/sh -i
> Launching a new sandboxed process.
> # :> Y
> cannot create Y: Operation not permitted
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>

...

> +SEC("landlock1")
> +static int landlock_fs_prog1(struct landlock_context *ctx)
> +{
> + char fmt_error_mode[] = "landlock1: error: get_mode:%lld\n";
> + char fmt_error_access[] = "landlock1: error: access denied\n";
> + long long ret;
> +
> + /*
> + * The argument ctx->arg2 contains bitflags of actions for which the
> + * rule is run. The flag LANDLOCK_ACTION_FS_WRITE means that a write
> + * is requested by one of the userspace processes restricted by this
> + * rule. The following test allows any actions which does not include a
> + * write.
> + */
> + if (!(ctx->arg2 & LANDLOCK_ACTION_FS_WRITE))
> + return 0;
> +
> + /*
> + * The argument ctx->arg1 is a file handle for which the process want
> + * to access. The function bpf_handle_fs_get_mode() return the mode of
> + * a file (e.g. S_IFBLK, S_IFDIR, S_IFREG...). If there is an error,
> + * for example if the argument is not a file handle, then an
> + * -errno value is returned. Otherwise the caller get the file mode as
> + * with stat(2).
> + */
> + ret = bpf_handle_fs_get_mode((void *)ctx->arg1);
> + if (ret < 0) {
> +
> + /*
> + * The bpf_trace_printk() function enable to write in the
> + * kernel eBPF debug log, accessible through
> + * /sys/kernel/debug/tracing/trace_pipe . To be allowed to call
> + * this function, a Landlock rule must have the
> + * LANDLOCK_SUBTYPE_ABILITY_DEBUG ability, which is only
> + * allowed for CAP_SYS_ADMIN.
> + */
> + bpf_trace_printk(fmt_error_mode, sizeof(fmt_error_mode), ret);
> + return 1;
> + }
> +
> + /*
> + * This check allows the action on the file if it is a directory or a
> + * pipe. Otherwise, a message is printed to the eBPF log.
> + */
> + if (S_ISCHR(ret) || S_ISFIFO(ret))
> + return 0;
> + bpf_trace_printk(fmt_error_access, sizeof(fmt_error_access));
> + return 1;
> +}
> +
> +/*
> + * This subtype enable to set the ABI, which ensure that the eBPF context and
> + * program behavior will be compatible with this Landlock rule.
> + */
> +SEC("subtype")
> +static const union bpf_prog_subtype _subtype = {
> + .landlock_rule = {
> + .abi = 1,
> + .event = LANDLOCK_SUBTYPE_EVENT_FS,
> + .ability = LANDLOCK_SUBTYPE_ABILITY_DEBUG,
> + }
> +};

from rule writer perspective can you somehow merge subtype definition
with the program? It seems they go hand in hand.
Like section name of the program can be:
SEC("landlock_rule1/event=fs/ability=debug")
static int landlock_fs_prog1(struct landlock_context *ctx)...
and the loader can parse this string and prepare appropriate
data structures for the kernel.

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