From 52dae5007588a756648637051973ab440df4d70b Mon Sep 17 00:00:00 2001 From: Juan RP Date: Fri, 13 Mar 2015 21:14:28 +0100 Subject: [PATCH] xbps-uunshare: replace clone/exec with unshare/exec cmd. There's no reason to clone and run cmd in the child, replace the execution environment with cmd directly to avoid the child process. --- NEWS | 3 + bin/xbps-uunshare/main.c | 142 ++++++++++++++++++--------------------- 2 files changed, 68 insertions(+), 77 deletions(-) diff --git a/NEWS b/NEWS index 40275547..fcbe11b8 100644 --- a/NEWS +++ b/NEWS @@ -1,5 +1,8 @@ xbps-0.44.1 (???): + * xbps-uunshare(8): does not fork and run cmd in the child process anymore, + replaces the execution environment with cmd instead. + * xbps-uunshare(8): do not fail if we cannot disable setgroups; some kernels might not support it. Found by @cheneukirchen on 3.16. diff --git a/bin/xbps-uunshare/main.c b/bin/xbps-uunshare/main.c index c3be5bef..dd42adfb 100644 --- a/bin/xbps-uunshare/main.c +++ b/bin/xbps-uunshare/main.c @@ -88,9 +88,8 @@ main(int argc, char **argv) uid_t uid = getuid(); gid_t gid = getgid(); const char *chrootdir, *distdir, *hostdir, *shmdir, *cmd, *argv0; - char **cmdargs, mountdir[PATH_MAX-1], buf[32]; - int fd, aidx = 0, clone_flags, child_status = 0; - pid_t child; + char **cmdargs, buf[32]; + int fd, aidx = 0; chrootdir = distdir = hostdir = shmdir = cmd = NULL; argv0 = argv[0]; @@ -128,84 +127,73 @@ main(int argc, char **argv) if (strcmp(chrootdir, "/") == 0) die("/ is not allowed to be used as chrootdir"); - clone_flags = (SIGCHLD|CLONE_NEWUSER|CLONE_NEWNS|CLONE_NEWIPC|CLONE_NEWUTS|CLONE_NEWPID); - - /* Issue the clone(2) syscall with our settings */ - if ((child = syscall(__NR_clone, clone_flags, NULL)) == -1) { + /* + * Unshare from the current process namespaces and set ours. + */ + if (unshare(CLONE_NEWUSER|CLONE_NEWNS|CLONE_NEWIPC|CLONE_NEWUTS) == -1) { errval = 99; - die("clone"); + die("unshare"); } + /* + * Setup uid/gid user mappings and restrict setgroups(). + */ + if ((fd = open("/proc/self/uid_map", O_RDWR)) == -1) + die("failed to open /proc/self/uidmap rw"); + if (write(fd, buf, snprintf(buf, sizeof buf, "%u %u 1\n", uid, uid)) == -1) + die("failed to write to /proc/self/uid_map"); - if (child == 0) { - /* - * Setup uid/gid user mappings and restrict setgroups(). - */ - if ((fd = open("/proc/self/uid_map", O_RDWR)) == -1) - die("failed to open /proc/self/uidmap rw"); - if (write(fd, buf, snprintf(buf, sizeof buf, "%u %u 1\n", uid, uid)) == -1) - die("failed to write to /proc/self/uid_map"); - + close(fd); + + if ((fd = open("/proc/self/setgroups", O_RDWR)) != -1) { + if (write(fd, "deny", 4) == -1) + die("failed to write to /proc/self/setgroups"); close(fd); - - if ((fd = open("/proc/self/setgroups", O_RDWR)) != -1) { - if (write(fd, "deny", 4) == -1) - die("failed to write to /proc/self/setgroups"); - close(fd); - } - - if ((fd = open("/proc/self/gid_map", O_RDWR)) == -1) - die("failed to open /proc/self/gid_map rw"); - if (write(fd, buf, snprintf(buf, sizeof buf, "%u %u 1\n", gid, gid)) == -1) - die("failed to write to /proc/self/gid_map"); - - close(fd); - - /* mount /proc */ - snprintf(mountdir, sizeof(mountdir), "%s/proc", chrootdir); - if (mount("proc", mountdir, "proc", MS_MGC_VAL|MS_PRIVATE, NULL) == -1) - die("Failed to mount %s", mountdir); - - /* bind mount /sys */ - bindmount(chrootdir, "/sys", NULL); - - /* bind mount /dev */ - bindmount(chrootdir, "/dev", NULL); - - /* bind mount hostdir if set */ - if (hostdir) - bindmount(chrootdir, hostdir, "/host"); - - /* bind mount distdir (if set) */ - if (distdir) - bindmount(chrootdir, distdir, "/void-packages"); - - /* bind mount shmdir (if set) */ - if (shmdir) - bindmount(chrootdir, shmdir, NULL); - - /* move chrootdir to / and chroot to it */ - if (chdir(chrootdir) == -1) - die("chdir to %s", chrootdir); - - if (mount(".", ".", NULL, MS_BIND|MS_PRIVATE, NULL) == -1) - die("Failed to bind mount %s", chrootdir); - - if (mount(chrootdir, "/", NULL, MS_MOVE, NULL) == -1) - die("Failed to move %s as rootfs", chrootdir); - - if (chroot(".") == -1) - die("Failed to chroot to %s", chrootdir); - - if (execvp(cmd, cmdargs) == -1) - die("Failed to execute command %s", cmd); } - /* Wait until the child terminates */ - while (waitpid(child, &child_status, 0) < 0) { - if (errno != EINTR) - die("waitpid"); - } - if (!WIFEXITED(child_status)) - return -1; - return WEXITSTATUS(child_status); + if ((fd = open("/proc/self/gid_map", O_RDWR)) == -1) + die("failed to open /proc/self/gid_map rw"); + if (write(fd, buf, snprintf(buf, sizeof buf, "%u %u 1\n", gid, gid)) == -1) + die("failed to write to /proc/self/gid_map"); + + close(fd); + + /* bind mount /proc */ + bindmount(chrootdir, "/proc", NULL); + + /* bind mount /sys */ + bindmount(chrootdir, "/sys", NULL); + + /* bind mount /dev */ + bindmount(chrootdir, "/dev", NULL); + + /* bind mount hostdir if set */ + if (hostdir) + bindmount(chrootdir, hostdir, "/host"); + + /* bind mount distdir (if set) */ + if (distdir) + bindmount(chrootdir, distdir, "/void-packages"); + + /* bind mount shmdir (if set) */ + if (shmdir) + bindmount(chrootdir, shmdir, NULL); + + /* move chrootdir to / and chroot to it */ + if (chdir(chrootdir) == -1) + die("chdir to %s", chrootdir); + + if (mount(".", ".", NULL, MS_BIND|MS_PRIVATE, NULL) == -1) + die("Failed to bind mount %s", chrootdir); + + if (mount(chrootdir, "/", NULL, MS_MOVE, NULL) == -1) + die("Failed to move %s as rootfs", chrootdir); + + if (chroot(".") == -1) + die("Failed to chroot to %s", chrootdir); + + if (execvp(cmd, cmdargs) == -1) + die("Failed to execute command %s", cmd); + + /* NOTREACHED */ + exit(EXIT_FAILURE); }