diff --git a/pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c b/pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c index 34e050dde4f..dcb2e97aa93 100644 --- a/pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c +++ b/pkgs/build-support/build-fhs-userenv/chrootenv/chrootenv.c @@ -7,32 +7,43 @@ #include #include +#include +#include +#include +#include +#include + #define fail(s, err) g_error("%s: %s: %s", __func__, s, g_strerror(err)) #define fail_if(expr) \ if (expr) \ fail(#expr, errno); -#include +const gchar *bind_blacklist[] = {"bin", "etc", "host", "real-host", "usr", "lib", "lib64", "lib32", "sbin", NULL}; -#include -#include -#include -#include - -int min(int a, int b) { - return a > b ? b : a; +int pivot_root(const char *new_root, const char *put_old) { + return syscall(SYS_pivot_root, new_root, put_old); } -const gchar *bind_blacklist[] = {"bin", "etc", "host", "usr", "lib", "lib64", "lib32", "sbin", NULL}; +void mount_tmpfs(const gchar *target) { + fail_if(mount("none", target, "tmpfs", 0, NULL)); +} void bind_mount(const gchar *source, const gchar *target) { fail_if(g_mkdir(target, 0755)); - fail_if(mount(source, target, "bind", MS_BIND | MS_REC, NULL)); + fail_if(mount(source, target, NULL, MS_BIND | MS_REC, NULL)); } -void bind_mount_host(const gchar *host, const gchar *guest) { +const gchar *create_tmpdir() { + gchar *prefix = + g_build_filename(g_get_tmp_dir(), "chrootenvXXXXXX", NULL); + fail_if(!g_mkdtemp_full(prefix, 0755)); + return prefix; +} + +void pivot_host(const gchar *guest) { g_autofree gchar *point = g_build_filename(guest, "host", NULL); - bind_mount(host, point); + fail_if(g_mkdir(point, 0755)); + fail_if(pivot_root(guest, point)); } void bind_mount_item(const gchar *host, const gchar *guest, const gchar *name) { @@ -44,19 +55,22 @@ void bind_mount_item(const gchar *host, const gchar *guest, const gchar *name) { } void bind(const gchar *host, const gchar *guest) { + mount_tmpfs(guest); + pivot_host(guest); + + g_autofree gchar *host_dir = g_build_filename("/host", host, NULL); + g_autoptr(GError) err = NULL; - g_autoptr(GDir) dir = g_dir_open(host, 0, &err); + g_autoptr(GDir) dir = g_dir_open(host_dir, 0, &err); if (err != NULL) fail("g_dir_open", errno); const gchar *item; - while (item = g_dir_read_name(dir)) + while ((item = g_dir_read_name(dir))) if (!g_strv_contains(bind_blacklist, item)) - bind_mount_item(host, guest, item); - - bind_mount_host(host, guest); + bind_mount_item(host_dir, "/", item); } void spit(const char *path, char *fmt, ...) { @@ -72,11 +86,6 @@ void spit(const char *path, char *fmt, ...) { fclose(f); } -int nftw_remove(const char *path, const struct stat *sb, int type, - struct FTW *ftw) { - return remove(path); -} - int main(gint argc, gchar **argv) { const gchar *self = *argv++; @@ -85,15 +94,7 @@ int main(gint argc, gchar **argv) { return 1; } - if (g_getenv("NIX_CHROOTENV")) - g_warning("chrootenv doesn't stack!"); - else - g_setenv("NIX_CHROOTENV", "", TRUE); - - g_autofree gchar *prefix = - g_build_filename(g_get_tmp_dir(), "chrootenvXXXXXX", NULL); - - fail_if(!g_mkdtemp_full(prefix, 0755)); + g_autofree const gchar *prefix = create_tmpdir(); pid_t cpid = fork(); @@ -119,9 +120,24 @@ int main(gint argc, gchar **argv) { spit("/proc/self/uid_map", "%d %d 1", uid, uid); spit("/proc/self/gid_map", "%d %d 1", gid, gid); - bind("/", prefix); + // If there is a /host directory, assume this is nested chrootenv and use it as host instead. + gboolean nested_host = g_file_test("/host", G_FILE_TEST_EXISTS | G_FILE_TEST_IS_DIR); + g_autofree const gchar *host = nested_host ? "/host" : "/"; + + bind(host, prefix); + + // Replace /host by an actual (inner) /host. + if (nested_host) { + fail_if(g_mkdir("/real-host", 0755)); + fail_if(mount("/host/host", "/real-host", NULL, MS_BIND | MS_REC, NULL)); + // For some reason umount("/host") returns EBUSY even immediately after + // pivot_root. We detach it at least to keep `/proc/mounts` from blowing + // up in nested cases. + fail_if(umount2("/host", MNT_DETACH)); + fail_if(mount("/real-host", "/host", NULL, MS_MOVE, NULL)); + fail_if(rmdir("/real-host")); + } - fail_if(chroot(prefix)); fail_if(chdir("/")); fail_if(execvp(*argv, argv)); } @@ -130,10 +146,7 @@ int main(gint argc, gchar **argv) { int status; fail_if(waitpid(cpid, &status, 0) != cpid); - // glibc 2.27 (and possibly other versions) can't handle - // an nopenfd value larger than 2^19 - fail_if(nftw(prefix, nftw_remove, min(getdtablesize(), 1<<19), - FTW_DEPTH | FTW_MOUNT | FTW_PHYS)); + fail_if(rmdir(prefix)); if (WIFEXITED(status)) return WEXITSTATUS(status);