diff options
Diffstat (limited to 'pkgs/build-support/build-sandbox/src/setup.c')
| -rw-r--r-- | pkgs/build-support/build-sandbox/src/setup.c | 709 |
1 files changed, 709 insertions, 0 deletions
diff --git a/pkgs/build-support/build-sandbox/src/setup.c b/pkgs/build-support/build-sandbox/src/setup.c new file mode 100644 index 00000000..f351ce19 --- /dev/null +++ b/pkgs/build-support/build-sandbox/src/setup.c @@ -0,0 +1,709 @@ +#define _GNU_SOURCE + +#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> + +#include "params.h" +#include "nix-query.h" +#include "path-cache.h" + +static path_cache cached_paths = NULL; + +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; \ + } + +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, bool do_cache) +{ + 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, do_cache)) { + free(tmp); + return false; + } + } + + if (!do_cache || cache_path(cached_paths, path)) + (void)mkdir(path, 0755); + free(tmp); + return true; +} + +static char *get_mount_target(const char *path) +{ + size_t pathlen = strlen(path), rootdir_len = strlen(FS_ROOT_DIR); + char *target; + + if ((target = malloc(rootdir_len + pathlen + 1)) == NULL) { + perror("malloc mount target"); + return NULL; + } + + memcpy(target, FS_ROOT_DIR, rootdir_len); + memcpy(target + rootdir_len, path, pathlen + 1); + return target; +} + +bool bind_mount(const char *path, bool restricted, bool resolve) +{ + int mflags = MS_BIND | MS_REC; + char src[PATH_MAX], *target; + + if (restricted) + mflags |= MS_NOSUID | MS_NODEV | MS_NOATIME; + + if (resolve ? realpath(path, src) == NULL : access(path, F_OK) == -1) + // Skip missing mount source + return true; + + if ((target = get_mount_target(resolve ? src : path)) == NULL) + return false; + + if (!makedirs(target, false)) { + free(target); + return false; + } + + if (!cache_path(cached_paths, resolve ? src : path)) { + free(target); + return true; + } + + if (mount(resolve ? src : path, target, "", mflags, NULL) == -1) { + fprintf(stderr, "mount %s to %s: %s\n", + resolve ? src : path, target, strerror(errno)); + free(target); + return false; + } + + free(target); + return true; +} + +static bool bind_file(const char *path) +{ + char *target, *tmp; + + if (access(path, R_OK) == -1) + // Skip missing mount source + return true; + + if ((target = get_mount_target(path)) == NULL) + return false; + + if ((tmp = strdup(target)) == NULL) { + perror("strdup bind file target path"); + free(target); + return false; + } + + if (!makedirs(dirname(tmp), true)) { + free(target); + free(tmp); + return false; + } + + free(tmp); + + if (!cache_path(cached_paths, path)) { + free(target); + return true; + } + + if (creat(target, 0666) == -1) { + fprintf(stderr, "unable to create %s: %s\n", target, strerror(errno)); + free(target); + return false; + } + + if (mount(path, target, "", MS_BIND, NULL) == -1) { + fprintf(stderr, "mount file %s to %s: %s\n", + path, target, strerror(errno)); + free(target); + return false; + } + + free(target); + 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); +} + +bool extra_mount(const char *path, bool is_required) +{ + char *expanded; + + if ((expanded = replace_env(path)) == NULL) + return false; + + if (is_required && !makedirs(expanded, false)) + return false; + + if (!bind_mount(expanded, true, true)) { + free(expanded); + return false; + } + + free(expanded); + return true; +} + +static bool setup_xauthority(void) +{ + char *xauth, *home; + bool result; + size_t homelen; + + if ((xauth = getenv("XAUTHORITY")) != NULL) + return bind_file(xauth); + + if ((home = getenv("HOME")) == NULL) { + fputs("Unable find $HOME.\n", stderr); + return false; + } + + homelen = strlen(home); + + if ((xauth = malloc(homelen + 13)) == NULL) { + perror("malloc xauth file path"); + return false; + } + + memcpy(xauth, home, homelen); + memcpy(xauth + homelen, "/.Xauthority", 13); + + result = bind_file(xauth); + free(xauth); + return result; +} + +static bool is_dir(const char *path) +{ + struct stat sb; + if (stat(path, &sb) == -1) { + fprintf(stderr, "stat %s: %s\n", path, strerror(errno)); + // Default to directory for mounting + return true; + } + return S_ISDIR(sb.st_mode); +} + +static bool mount_requisites(struct query_state *qs, const char *path) +{ + const char *requisite; + + if (!query_requisites(qs, path)) { + fprintf(stderr, "Unable to get requisites for %s.\n", path); + return false; + } + + while ((requisite = next_query_result(qs)) != NULL) { + if (is_dir(requisite)) { + if (!bind_mount(requisite, true, false)) + return false; + } else { + if (!bind_file(requisite)) + return false; + } + } + + return true; +} + +bool mount_from_path_var(struct query_state *qs, const char *name) +{ + char *buf, *ptr, *value = getenv(name); + + if (value == NULL) + return true; + + if ((buf = strdup(value)) == NULL) { + fprintf(stderr, "strdup %s: %s\n", value, strerror(errno)); + return false; + } + + ptr = strtok(buf, ":"); + + while (ptr != NULL) { + if (!mount_requisites(qs, ptr)) { + free(buf); + return false; + } + ptr = strtok(NULL, ":"); + } + + free(buf); + return true; +} + +static bool setup_static_etc(struct query_state *qs) +{ + char dest[PATH_MAX]; + ssize_t destlen; + + if ((destlen = readlink("/etc/static", dest, PATH_MAX)) == -1) + return true; + + if (destlen >= PATH_MAX) { + fputs("readlink of /etc/static larger than PATH_MAX.\n", stderr); + return false; + } + + dest[destlen] = '\0'; + return mount_requisites(qs, dest); +} + +static bool setup_runtime_paths(void) +{ + struct query_state *qs; + + if ((qs = new_query()) == NULL) { + fputs("Unable to allocate Nix query state.\n", stderr); + return false; + } + + if (!setup_static_etc(qs)) { + free_query(qs); + return false; + } + + if (!mount_runtime_path_vars(qs)) { + free_query(qs); + return false; + } + + free_query(qs); + return true; +} + +static bool setup_chroot(void) +{ + int mflags; + + mflags = MS_NOEXEC | MS_NOSUID | MS_NODEV | MS_NOATIME; + + if (mount("none", FS_ROOT_DIR, "tmpfs", mflags, NULL) == -1) { + perror("mount rootfs"); + return false; + } + + if (!bind_mount("/etc", true, false)) + return false; + + if (!bind_mount("/dev", false, false)) + return false; + + if (!bind_mount("/proc", false, false)) + return false; + + if (!bind_mount("/sys", false, false)) + return false; + + if (!bind_mount("/run", false, false)) + return false; + + if (!bind_mount("/var/run", false, false)) + return false; + + if (!bind_mount("/tmp", true, false)) + return false; + + if (!setup_runtime_paths()) + return false; + + if (!setup_app_paths()) + return false; + + if (!setup_xauthority()) + return false; + + if (chroot(FS_ROOT_DIR) == -1) { + perror("chroot"); + return false; + } + + if (chdir("/") == -1) { + perror("chdir rootfs"); + return false; + } + + return true; +} + +bool setup_sandbox(void) +{ + int sync_pipe[2]; + char sync_status = '.'; + int child_status; + pid_t pid, parent_pid; + + if (pipe(sync_pipe) == -1) { + perror("pipe"); + return false; + } + + parent_pid = getpid(); + + switch (pid = fork()) { + case -1: + perror("fork"); + return false; + 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 false; + } + + close(sync_pipe[1]); + waitpid(pid, &child_status, 0); + if (WIFEXITED(child_status) && WEXITSTATUS(child_status) == 0) + break; + return false; + } + + cached_paths = new_path_cache(); + + if (!setup_chroot()) { + free_path_cache(cached_paths); + return false; + } + + free_path_cache(cached_paths); + return true; +} |