From 1e7713c8a39fe541a4de107f775765d29ea78e10 Mon Sep 17 00:00:00 2001 From: Sangbum Kim Date: Tue, 2 Jan 2024 00:04:24 +0900 Subject: [PATCH] added intial commmit --- .dockerignore | 4 +++ .gitignore | 2 ++ CMakeLists.txt | 36 +++++++++++++++++++++++++++ Dockerfile | 11 +++++++++ LICENSE | 21 ++++++++++++++++ README.md | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++ config.h.in | 6 +++++ lgtm.yml | 4 +++ setcap.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++ 9 files changed, 217 insertions(+) create mode 100644 .dockerignore create mode 100644 .gitignore create mode 100644 CMakeLists.txt create mode 100644 Dockerfile create mode 100644 LICENSE create mode 100644 README.md create mode 100644 config.h.in create mode 100644 lgtm.yml create mode 100644 setcap.c diff --git a/.dockerignore b/.dockerignore new file mode 100644 index 0000000..ce1b641 --- /dev/null +++ b/.dockerignore @@ -0,0 +1,4 @@ +* +!CMakeLists.txt +!setcap.c +!config.h.in diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..00a6291 --- /dev/null +++ b/.gitignore @@ -0,0 +1,2 @@ +/.vscode +/build diff --git a/CMakeLists.txt b/CMakeLists.txt new file mode 100644 index 0000000..b5b0b01 --- /dev/null +++ b/CMakeLists.txt @@ -0,0 +1,36 @@ +cmake_minimum_required(VERSION 3.0) + +if(POLICY CMP0056) + cmake_policy(SET CMP0056 NEW) +endif() +if(POLICY CMP0065) + cmake_policy(SET CMP0065 NEW) +endif() +if(POLICY CMP0066) + cmake_policy(SET CMP0066 NEW) +endif() + +set(CMAKE_FIND_LIBRARY_SUFFIXES "${CMAKE_STATIC_LIBRARY_SUFFIX}") +set(CMAKE_EXE_LINKER_FLAGS "-static") +set(CMAKE_ENABLE_EXPORTS Off) + +include(CheckFunctionExists) + +project(setcap-static VERSION 1.0.0 LANGUAGES C) + +find_path(NAMES sys/capability.h REQUIRED) +find_library(LIBCAP_LIBRARY NAMES "${CMAKE_STATIC_LIBRARY_PREFIX}cap${CMAKE_STATIC_LIBRARY_SUFFIX}" cap) +if(NOT LIBCAP_LIBRARY) + message(FATAL_ERROR "Unable to find libcap") +endif() +add_library(libcap STATIC IMPORTED) +set_target_properties(libcap PROPERTIES IMPORTED_LOCATION ${LIBCAP_LIBRARY}) + +set(CMAKE_REQUIRED_LIBRARIES "${LIBCAP_LIBRARY};${CMAKE_REQUIRED_LIBRARIES}") +check_function_exists(cap_set_nsowner HAVE_CAP_SET_NSOWNER) + +configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in ${CMAKE_CURRENT_BINARY_DIR}/config.h) + +add_executable(setcap-static setcap.c) +target_link_libraries(setcap-static libcap) +target_include_directories(setcap-static PUBLIC ${PROJECT_BINARY_DIR}) diff --git a/Dockerfile b/Dockerfile new file mode 100644 index 0000000..0defbac --- /dev/null +++ b/Dockerfile @@ -0,0 +1,11 @@ +FROM harbor.repository.lb.home.dc.internal.amuz.es/infrastructure/alpine-base:3.19-latest AS build +RUN apk add --no-cache cmake make musl-dev gcc libcap-static libcap-dev +WORKDIR /build +COPY . . +RUN \ + cmake -S . -B build -DCMAKE_BUILD_TYPE=MinSizeRel && \ + cmake --build build --config MinSizeRel && \ + strip build/setcap-static + +FROM scratch +COPY --from=build /build/build/setcap-static /setcap-static diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..4f7aa48 --- /dev/null +++ b/LICENSE @@ -0,0 +1,21 @@ +MIT License + +Copyright (c) 2021 Volodymyr Kolesnykov + +Permission is hereby granted, free of charge, to any person obtaining a copy +of this software and associated documentation files (the "Software"), to deal +in the Software without restriction, including without limitation the rights +to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the Software is +furnished to do so, subject to the following conditions: + +The above copyright notice and this permission notice shall be included in all +copies or substantial portions of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +SOFTWARE. diff --git a/README.md b/README.md new file mode 100644 index 0000000..e164ea4 --- /dev/null +++ b/README.md @@ -0,0 +1,67 @@ +# setcap-static + +[![Build](https://github.com/sjinks/setcap-static/actions/workflows/build.yml/badge.svg)](https://github.com/sjinks/setcap-static/actions/workflows/build.yml) +[![Docker CI/CD](https://github.com/sjinks/setcap-static/actions/workflows/docker.yml/badge.svg)](https://github.com/sjinks/setcap-static/actions/workflows/docker.yml) +[![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/sjinks/setcap-static.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/sjinks/setcap-static/context:cpp) +![Docker Image Size](https://img.shields.io/docker/image-size/wildwildangel/setcap-static/latest) + +`setcap-static` is a statically linked trimmed down version of [setcap(8)](https://linux.die.net/man/8/setcap). It sets the capabilities of the given filename to the capabilities specified. + +## Why + +KubeSec security guidelines suggest that the running image should be "run as a [non-root user to ensure the least privilege](https://kubesec.io/basics/containers-securitycontext-runasnonroot-true/)." However, if the containerized application needs some `root` privileges (like binding to a port less than 1024) and runs in a `scratch` image, this will not be straightforward. + +The issue is that Docker's `COPY` command does not preserve the extended attributes; therefore, you cannot do something like this: + +```Dockerfile +FROM alpine:3.13 as build + +# ... + +RUN \ + apk add --no-cache libcap \ + && setcap 'cap_net_bind_service=+ep' my-cool-application \ + && apk del --no-cache libcap + +# ... + +FROM scratch +COPY --from=build /path/to/my-cool-application /my-cool-application +``` + +In the target image, `my-cool-application` will not have the capabilities set in the `build` image. Therefore, if you need to grant some capabilities to your application, you have to do it in the target image. You cannot just copy `setcap` from Alpine — because it is a dynamically linked executable (it depends on ld-musl, libcap, libc.musl). + +Here comes `libcap-static`. It is a lightweight version of `libcap`: it can only set the capabilities on a file, it does not support all other options of `libcap`. + +Unlike `libcap`, `libcap-static` has an option to delete itself: this can be handy for `scratch` images if you don't want to leave any other executables than your application visible to the user (or an attacker). If `libcap-static` detects that the first two characters of `argv[0]` are `/!`, it will delete itself after the successful operation. + +For example, + +```Dockerfile +FROM scratch +COPY --from=wildwildangel/setcap-static /setcap-static /!setcap-static +COPY --from=build /build/build/tiny-ssh-honeypot /tiny-ssh-honeypot +RUN ["/!setcap-static", "cap_net_bind_service=+ep", "/tiny-ssh-honeypot"] +``` + +After granting the `CAP_NET_BIND_SERVICE` capability to `tiny-ssh-honeypot`, `libcap-static` will delete itself. + +## Build + +Build dependencies: + * Alpine: cmake, make, libcap-dev, libcap-static + * Ubuntu: cmake, make, libcap-dev + +```bash +cmake -S . -B build -DCMAKE_BUILD_TYPE=MinSizeRel +cmake --build build --config MinSizeRel +``` + +## Usage + +```bash +setcap-static capabilities filename +``` + + * `capabilities` is the list of capabilities in the form supported by [`cap_from_text(3)`](https://linux.die.net/man/3/cap_from_text) (or by `setcap`) + * `filename` is the name of the file to operate on; it must not refer to a symlink. diff --git a/config.h.in b/config.h.in new file mode 100644 index 0000000..2bab62f --- /dev/null +++ b/config.h.in @@ -0,0 +1,6 @@ +#ifndef A654D99F_22CB_438F_A0D3_6659AC64CE80 +#define A654D99F_22CB_438F_A0D3_6659AC64CE80 + +#cmakedefine HAVE_CAP_SET_NSOWNER 1 + +#endif /* A654D99F_22CB_438F_A0D3_6659AC64CE80 */ diff --git a/lgtm.yml b/lgtm.yml new file mode 100644 index 0000000..40a2b1b --- /dev/null +++ b/lgtm.yml @@ -0,0 +1,4 @@ +extraction: + cpp: + prepare: + packages: "libcap-dev" diff --git a/setcap.c b/setcap.c new file mode 100644 index 0000000..424cc9f --- /dev/null +++ b/setcap.c @@ -0,0 +1,66 @@ +#include +#include +#include +#include +#include "config.h" + +int main(int argc, char** argv) +{ + if (argc != 3) { + fprintf(stderr, "Usage: setcap capabilities filename\n"); + return argc == 1 ? EXIT_SUCCESS : EXIT_FAILURE; + } + + cap_t my_caps = cap_get_proc(); + if (my_caps == NULL) { + perror("cap_get_proc"); + return EXIT_FAILURE; + } + + cap_t target_caps = cap_from_text(argv[1]); + if (target_caps == NULL) { + perror("cap_from_text"); + cap_free(my_caps); + return EXIT_FAILURE; + } + +#ifdef HAVE_CAP_SETNSOWNER + if (cap_set_nsowner(target_caps, 0)) { + perror("cap_set_nsowner"); + cap_free(my_caps); + cap_free(target_caps); + return EXIT_FAILURE; + } +#endif + + cap_value_t flag = CAP_SETFCAP; + if (cap_set_flag(my_caps, CAP_EFFECTIVE, 1, &flag, CAP_SET) != 0) { + perror("cap_set_flag(CAP_SETFCAP)"); + cap_free(my_caps); + cap_free(target_caps); + return EXIT_FAILURE; + } + + if (cap_set_proc(my_caps) != 0) { + perror("cap_set_proc"); + cap_free(my_caps); + cap_free(target_caps); + return EXIT_FAILURE; + } + + cap_free(my_caps); + + if (cap_set_file(argv[2], target_caps) != 0) { + perror("cap_set_file"); + cap_free(target_caps); + return EXIT_FAILURE; + } + + cap_free(target_caps); + + if (argv[0][0] == '/' && argv[0][1] == '!') { + unlink(argv[0]); + } + + return EXIT_SUCCESS; +}