privsepcomp/example_secure_cmd.c at main · markkdown/privsepcomp · GitHub

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#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <seccomp.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>

void usage(const char *prog) {
    fprintf(stderr, "Usage: %s [-c|-i|-d] <filename>\n", prog);
    fprintf(stderr, "  -c    create file\n");
    fprintf(stderr, "  -i    show file info (size)\n");
    fprintf(stderr, "  -d    delete file\n");
}

int main(int argc, char *argv[]) {

    pid_t pid = fork();

    if (pid == 0) {

        scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_KILL);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(set_tid_address), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(ioctl), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(close), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(pread64), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getrandom), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(execve), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mmap), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(openat), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(read), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(prlimit64), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(newfstatat), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(rseq), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(arch_prctl), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(munmap), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(mprotect), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(fstat), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(unlink), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(set_robust_list), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(brk), 0);
        seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(access), 0);

        if (seccomp_load(ctx) < 0) {
            perror("seccomp_load failed");
            exit(1);
        }

        int opt;
        char action = 0;

        while ((opt = getopt(argc, argv, "cid")) != -1) {
            switch (opt) {
                case 'c':
                case 'i':
                case 'd':
                    action = opt;
                    break;
                default:
                    usage(argv[0]);
                    return 1;
            }
        }

        if (optind >= argc) {
            fprintf(stderr, "Missing file name.\n");
            usage(argv[0]);
            return 1;
        }

        const char *filename = argv[optind];

        switch (action) {
            case 'c': {
                FILE *f = fopen(filename, "w");
                if (!f) {
                    perror("fopen");
                    return 1;
                }
                fclose(f);
                printf("Created file '%s'.\n", filename);
                break;
            }
            case 'i': {
                struct stat st;
                if (stat(filename, &st) == 0) {
                    printf("File %s: %ld Bytes\n", filename, st.st_size);
                } else {
                    perror("stat");
                }
                break;
            }
            case 'd': {
                if (unlink(filename) == 0) {
                    printf("File '%s' deleted.\n", filename);
                } else {
                    perror("unlink");
                }
                break;
            }
            default:
                usage(argv[0]);
                return 1;
        }

        return 0;

    } else if (pid > 0) {
        if (setuid(1000) < 0) {
            perror("setuid failed");
            exit(1);
        }
        int status;
        waitpid(pid, &status, 0);
    } else {
        perror("Fork failed");
    }

}