pkgs/build-game: Introduce buildSandbox

So far creating the sandbox has been a setup hook, however it's a bit
ugly how we gathered the needed paths for the chroot file system by
recursively searching for store paths.

While I'd like to have the sandbox being built within the main
derivation, it really isn't very practical when the build takes longer
than 10 minutes.

With this implementation however the sandbox builds really fast and we
can also modify the sandbox without needing to rebuild a particular
game.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

2 files changed, 557 insertions, 0 deletions

diff --git a/pkgs/games/build-support/build-sandbox/default.nix b/pkgs/games/build-support/build-sandbox/default.nix
new file mode 100644
index 00000000..3b41e1bd
--- /dev/null
+++ b/pkgs/games/build-support/build-sandbox/default.nix
@@ -0,0 +1,60 @@
+{ stdenv, lib }:
+
+drv: { extraSandboxPaths ? [], ... }@attrs:
+
+stdenv.mkDerivation ({
+  name = "${drv.name}-sandboxed";
+
+  src = drv;
+
+  phases = [ "buildPhase" "installPhase" ];
+
+  exportReferencesGraph = [ "sandbox-closure" drv ];
+
+  buildPhase = ''
+    runtimeDeps="$(sed -ne '
+      p; n; n
+
+      :cdown
+      /^0*$/b
+      :l; s/0\(X*\)$/X\1/; tl
+
+      s/^\(X*\)$/9\1/; tdone
+      ${lib.concatMapStrings (num: ''
+        s/${toString num}\(X*\)$/${toString (num - 1)}\1/; tdone
+      '') (lib.range 1 9)}
+
+      :done
+      y/X/9/
+      x; n; p; x
+      bcdown
+    ' sandbox-closure | sort -u)"
+
+    echo 'static bool setup_app_paths(void) {' > params.c
+
+    for dep in $runtimeDeps; do
+      echo 'if (!bind_mount("'"$dep"'", true)) return false;' >> params.c
+    done
+
+    ${lib.concatMapStrings (extra: let
+      escaped = lib.escapeShellArg (lib.escape ["\\" "\""] extra);
+      result = "echo 'if (!extra_mount(\"'${escaped}'\")) return false;'";
+    in "${result} >> params.c") extraSandboxPaths}
+
+    echo 'return true; }' >> params.c
+    cat params.c
+  '';
+
+  installPhase = ''
+    mkdir -p "$out/bin"
+    for bin in "$src"/bin/*; do
+      progname="$(basename "$bin")"
+      gcc -g -std=gnu11 -Wall \
+        -DWRAPPED_PATH=\""$bin"\" \
+        -DWRAPPED_PROGNAME=\""$progname"\" \
+        -DPARAMS_FILE=\""$(pwd)/params.c"\" \
+        -o "$out/bin/$progname" ${./sandbox.c}
+    done
+  '';
+
+} // removeAttrs attrs [ "extraSandboxPaths" ])
diff --git a/pkgs/games/build-support/build-sandbox/sandbox.c b/pkgs/games/build-support/build-sandbox/sandbox.c
new file mode 100644
index 00000000..69553628
--- /dev/null
+++ b/pkgs/games/build-support/build-sandbox/sandbox.c
@@ -0,0 +1,497 @@
+#define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L
+
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <libgen.h>
+#include <limits.h>
+#include <malloc.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static bool write_proc(int proc_pid_fd, const char *fname, const char *buf,
+                       size_t buflen, bool ignore_errors)
+{
+    int fd;
+
+    if ((fd = openat(proc_pid_fd, fname, O_WRONLY)) == -1) {
+        fprintf(stderr, "open %s: %s\n", fname, strerror(errno));
+        return false;
+    }
+
+    if (write(fd, buf, buflen) == -1) {
+        if (!ignore_errors)
+            fprintf(stderr, "write %s: %s\n", fname, strerror(errno));
+        close(fd);
+        return ignore_errors;
+    }
+
+    close(fd);
+    return true;
+}
+
+#define WRITE_IDMAP(file, value) \
+    buflen = snprintf(buf, 100, "%1$lu %1$lu 1", (unsigned long)value); \
+    if (buflen >= 100) { \
+        fputs("Unable to write buffer for " file ".\n", stderr); \
+        close(proc_pid_fd); \
+        return false; \
+    } else if (buflen < 0) { \
+        perror("snprintf " file " buffer"); \
+        close(proc_pid_fd); \
+        return false; \
+    } \
+    if (!write_proc(proc_pid_fd, file, buf, buflen, false)) { \
+        close(proc_pid_fd); \
+        return false; \
+    }
+
+static bool write_maps(pid_t parent_pid)
+{
+    int proc_pid_fd;
+    size_t buflen;
+    char buf[100];
+
+    buflen = snprintf(buf, 100, "/proc/%lu", (unsigned long)parent_pid);
+    if (buflen >= 100) {
+        fputs("Unable to write buffer for child pid proc path.\n", stderr);
+        return false;
+    } else if (buflen < 0) {
+        perror("snprintf child pid proc path");
+        return false;
+    }
+
+    if ((proc_pid_fd = open(buf, O_RDONLY | O_DIRECTORY)) == -1) {
+        fprintf(stderr, "open %s: %s\n", buf, strerror(errno));
+        return false;
+    }
+
+    WRITE_IDMAP("uid_map", geteuid());
+
+    // Kernels prior to Linux 3.19 which do not impose setgroups()
+    // restrictions won't have this file, so ignore failure.
+    write_proc(proc_pid_fd, "setgroups", "deny", 4, true);
+
+    WRITE_IDMAP("gid_map", getegid());
+
+    return true;
+}
+
+static bool makedirs(const char *path)
+{
+    char *tmp, *segment;
+
+    if ((tmp = strdup(path)) == NULL) {
+        fprintf(stderr, "strdup of %s: %s\n", path, strerror(errno));
+        return false;
+    }
+
+    segment = dirname(tmp);
+
+    if (!(segment[0] == '/' && segment[1] == '\0')) {
+        if (!makedirs(segment)) {
+            free(tmp);
+            return false;
+        }
+    }
+
+    (void)mkdir(path, 0755);
+    free(tmp);
+    return true;
+}
+
+static bool bind_mount(const char *path, bool restricted)
+{
+    int mflags = MS_BIND | MS_REC;
+    size_t srclen;
+    char src[PATH_MAX], target[PATH_MAX];
+
+    if (restricted)
+        mflags |= MS_NOSUID | MS_NODEV | MS_NOATIME;
+
+    if (realpath(path, src) == NULL) {
+        fprintf(stderr, "realpath of %s: %s\n", path, strerror(errno));
+        return false;
+    }
+
+    if ((srclen = strlen(src)) > PATH_MAX - 4) {
+        fprintf(stderr, "`/tmp/%s' does not fit in PATH_MAX.\n", src);
+        return false;
+    }
+
+    memcpy(target, "/tmp", 4);
+    memcpy(target + 4, src, srclen + 1);
+
+    if (!makedirs(target))
+        return false;
+
+    if (mount(src, target, "", mflags, NULL) == -1) {
+        fprintf(stderr, "mount %s to %s: %s\n", src, target, strerror(errno));
+        return false;
+    }
+
+    return true;
+}
+
+struct envar_offset {
+    int start;
+    int length;
+    int var_start;
+    int var_length;
+    struct envar_offset *next;
+};
+
+static struct envar_offset *alloc_offset(void)
+{
+    struct envar_offset *new_offset;
+    new_offset = malloc(sizeof(struct envar_offset));
+
+    if (new_offset == NULL) {
+        perror("malloc envar_offset");
+        return NULL;
+    }
+
+    new_offset->next = NULL;
+    return new_offset;
+}
+
+static struct envar_offset *push_offset(struct envar_offset *current,
+                                        struct envar_offset **base)
+{
+    if (current == NULL) {
+        if ((current = alloc_offset()) != NULL)
+            *base = current;
+        return current;
+    }
+
+    return current->next = alloc_offset();
+}
+
+static void free_offsets(struct envar_offset *base)
+{
+    struct envar_offset *next;
+    if (base == NULL)
+        return;
+    next = base->next;
+    free(base);
+    if (next != NULL)
+        free_offsets(next);
+}
+
+static char *expand_xdg_fallback(const char *xdg_var)
+{
+    static char *home = NULL;
+    static size_t homelen;
+    char *result;
+
+    if (home == NULL) {
+        if ((home = getenv("HOME")) == NULL) {
+            fputs("Unable find $HOME.\n", stderr);
+            return NULL;
+        }
+        homelen = strlen(home);
+    }
+
+    if (strcmp(xdg_var, "XDG_DATA_HOME") == 0) {
+        result = malloc(homelen + 14);
+        if (result == NULL) {
+            perror("malloc XDG_DATA_HOME");
+            return NULL;
+        }
+        memcpy(result, home, homelen);
+        memcpy(result + homelen, "/.local/share", 14);
+        return result;
+    } else if (strcmp(xdg_var, "XDG_CONFIG_HOME") == 0) {
+        result = malloc(homelen + 9);
+        if (result == NULL) {
+            perror("malloc XDG_CONFIG_HOME");
+            return NULL;
+        }
+        memcpy(result, home, homelen);
+        memcpy(result + homelen, "/.config", 9);
+        return result;
+    }
+
+    return NULL;
+}
+
+static char *get_offset_var(struct envar_offset *offset, const char *haystack)
+{
+    char *tmp, *result;
+
+    tmp = strndup(haystack + offset->var_start, offset->var_length);
+
+    if (tmp == NULL) {
+        perror("strndup");
+        return NULL;
+    }
+
+    result = getenv(tmp);
+    if (result == NULL) {
+        if ((result = expand_xdg_fallback(tmp)) == NULL) {
+            fprintf(stderr, "Unable find variable %s in %s\n", tmp, haystack);
+            free(tmp);
+            return NULL;
+        }
+        free(tmp);
+        return result;
+    }
+    free(tmp);
+    return strdup(result);
+}
+
+static char *replace_env_offset_free(const char *path,
+                                     struct envar_offset *offset)
+{
+    struct envar_offset *tmp_offset;
+    size_t buflen, pathlen, varlen, tmplen;
+    int inpos = 0, outpos = 0;
+    char *buf, *curvar;
+
+    buflen = pathlen = strlen(path);
+
+    if ((buf = malloc(buflen + 1)) == NULL) {
+        perror("malloc replace_env buffer");
+        return NULL;
+    }
+
+    while (offset != NULL) {
+        if ((curvar = get_offset_var(offset, path)) == NULL) {
+            free(buf);
+            free_offsets(offset);
+            return NULL;
+        }
+
+        varlen = strlen(curvar);
+        tmplen = varlen + (buflen - offset->length);
+
+        if (tmplen > buflen) {
+            if ((buf = realloc(buf, (buflen = tmplen) + 1)) == NULL) {
+                perror("realloc replace_env buffer");
+                free(buf);
+                free(curvar);
+                free_offsets(offset);
+                return NULL;
+            }
+        }
+
+        memcpy(buf + outpos, path + inpos, offset->start - inpos);
+        outpos += offset->start - inpos;
+        inpos = offset->start;
+
+        memcpy(buf + outpos, curvar, varlen);
+        outpos += varlen;
+        inpos += offset->length;
+
+        free(curvar);
+
+        tmp_offset = offset;
+        offset = offset->next;
+        free(tmp_offset);
+    }
+
+    memcpy(buf + outpos, path + inpos, pathlen - inpos);
+    *(buf + outpos + (pathlen - inpos)) = '\0';
+
+    return buf;
+}
+
+static char *replace_env(const char *path)
+{
+    int i = 0, start = 0, var_start = 0;
+    size_t pathlen;
+    bool in_var = false, curly = false;
+    struct envar_offset *base = NULL, *offset = NULL;
+
+    pathlen = strlen(path);
+
+    while (i < pathlen) {
+        if (path[i] == '$' && !curly && !in_var) {
+            if (i + 1 >= pathlen)
+                break;
+
+            start = i;
+
+            if (path[i + 1] == '{') {
+                curly = true;
+                var_start = i + 2;
+                ++i;
+            } else {
+                in_var = true;
+                var_start = i + 1;
+            }
+        } else if (in_var) {
+            if (!(path[i] >= 'a' && path[i] <= 'z') &&
+                !(path[i] >= 'A' && path[i] <= 'Z') &&
+                !(path[i] >= '0' && path[i] <= '9') &&
+                path[i] != '_'
+            ) {
+                in_var = false;
+
+                if ((offset = push_offset(offset, &base)) == NULL) {
+                    free_offsets(base);
+                    return NULL;
+                }
+
+                offset->start = start;
+                offset->length = i - start;
+                offset->var_start = var_start;
+                offset->var_length = i - var_start;
+                continue;
+            }
+        } else if (curly) {
+            if (path[i] == '}') {
+                curly = false;
+
+                if ((offset = push_offset(offset, &base)) == NULL) {
+                    free_offsets(base);
+                    return NULL;
+                }
+
+                offset->start = start;
+                offset->length = (i + 1) - offset->start;
+                offset->var_start = var_start;
+                offset->var_length = i - offset->var_start;
+            }
+        }
+
+        ++i;
+    }
+
+    if (in_var) {
+        if ((offset = push_offset(offset, &base)) == NULL) {
+            free_offsets(base);
+            return NULL;
+        }
+
+        offset->start = start;
+        offset->length = i - start;
+        offset->var_start = var_start;
+        offset->var_length = i - var_start;
+    }
+
+    return replace_env_offset_free(path, base);
+}
+
+static bool extra_mount(const char *path)
+{
+    char *expanded;
+    if ((expanded = replace_env(path)) == NULL)
+        return false;
+
+    if (!bind_mount(expanded, true)) {
+        free(expanded);
+        return false;
+    }
+
+    free(expanded);
+    return true;
+}
+
+#include PARAMS_FILE
+
+static bool setup_chroot(void)
+{
+    int mflags;
+
+    mflags = MS_NOEXEC | MS_NOSUID | MS_NODEV | MS_NOATIME;
+
+    if (mount("none", "/tmp", "tmpfs", mflags, NULL) == -1) {
+        perror("mount rootfs");
+        return false;
+    }
+
+    if (!bind_mount("/dev", false))
+        return false;
+
+    if (!bind_mount("/proc", false))
+        return false;
+
+    if (!bind_mount("/sys", false))
+        return false;
+
+    if (mkdir("/tmp/tmp", 0700) == -1) {
+        perror("mkdir private tmp");
+        return false;
+    }
+
+    if (!setup_app_paths())
+        return false;
+
+    if (chroot("/tmp") == -1) {
+        perror("chroot");
+        return false;
+    }
+
+    if (chdir("/") == -1) {
+        perror("chdir rootfs");
+        return false;
+    }
+
+    return true;
+}
+
+int main(int argc, char **argv)
+{
+    int sync_pipe[2];
+    char sync_status = '.';
+    int child_status;
+    pid_t pid, parent_pid;
+
+    if (pipe(sync_pipe) == -1) {
+        perror("pipe");
+        return 1;
+    }
+
+    parent_pid = getpid();
+
+    switch (pid = fork()) {
+        case -1:
+            perror("fork");
+            return 1;
+        case 0:
+            close(sync_pipe[1]);
+            if (read(sync_pipe[0], &sync_status, 1) == -1) {
+                perror("read pipe from parent");
+                _exit(1);
+            } else if (sync_status == 'X')
+                _exit(1);
+            close(sync_pipe[0]);
+            _exit(write_maps(parent_pid) ? 0 : 1);
+        default:
+            if (unshare(CLONE_NEWNS | CLONE_NEWUSER) == -1) {
+                perror("unshare");
+                if (write(sync_pipe[1], "X", 1) == -1)
+                    perror("signal child exit");
+                waitpid(pid, NULL, 0);
+                return 1;
+            }
+
+            close(sync_pipe[1]);
+            waitpid(pid, &child_status, 0);
+            if (WIFEXITED(child_status) && WEXITSTATUS(child_status) == 0)
+                break;
+            return 1;
+    }
+
+    if (!setup_chroot())
+        return 1;
+
+    argv[0] = WRAPPED_PROGNAME;
+    if (execv(WRAPPED_PATH, argv) == -1) {
+        fprintf(stderr, "exec %s: %s\n", WRAPPED_PATH, strerror(errno));
+        return 1;
+    }
+
+    // Should never be reached.
+    return 1;
+}