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chrootenv: code review

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* Wrap LEN macro in parantheses
* Drop env_filter in favor of stateful environ_blacklist_filter,
  use execvp instead of execvpe, don't explicitly use environ
* Add argument error logging wherever it makes sense
* Drop strjoin in favor of asprintf
* char* -> const char* where appropriate
* Handle stat errors
* Print user messages with fputs, not errorf
* Abstract away is_str_in (previously bind_blacklisted)
* Cleanup temporary directory on error
* Some minor syntactic and naming changes

Thanks to Jörg Thalheim and Tuomas Tynkkynen for the code review!
This commit is contained in:
Yegor Timoshenko 2017-12-21 02:58:58 +00:00
parent 710662be94
commit 73a0d95b96
1 changed files with 90 additions and 100 deletions
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188
pkgs/build-support/build-fhs-userenv/chrootenv.c
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@ -21,101 +21,75 @@
#include <sys/stat.h> #include <sys/stat.h>
#include <sys/wait.h> #include <sys/wait.h>
#define LEN(x) sizeof(x) / sizeof(*x) #define LEN(x) (sizeof(x) / sizeof(*x))
char *env_blacklist[] = {}; // TODO: fill together with @abbradar when he gets better
const char *environ_blacklist[] = {};
char **env_filter(char *envp[]) { void environ_blacklist_filter() {
char **filtered_envp = malloc(sizeof(*envp)); for (size_t i = 0; i < LEN(environ_blacklist); i++) {
size_t n = 0; if (unsetenv(environ_blacklist[i]) < 0)
errorf(EX_OSERR, "unsetenv(%s)", environ_blacklist[i]);
while (*envp != NULL) {
bool blacklisted = false;
for (size_t i = 0; i < LEN(env_blacklist); i++) {
if (!strncmp(*envp, env_blacklist[i], strlen(env_blacklist[i]))) {
blacklisted = true;
break;
} }
} }
if (!blacklisted) { void bind(const char *from, const char *to) {
filtered_envp = realloc(filtered_envp, (n + 2) * sizeof(*envp));
if (filtered_envp == NULL)
errorf(EX_OSERR, "realloc");
filtered_envp[n++] = *envp;
}
envp++;
}
filtered_envp[n] = NULL;
return filtered_envp;
}
void bind(char *from, char *to) {
if (mkdir(to, 0755) < 0) if (mkdir(to, 0755) < 0)
errorf(EX_IOERR, "mkdir"); errorf(EX_IOERR, "mkdir(%s)", to);
if (mount(from, to, "bind", MS_BIND | MS_REC, NULL) < 0) if (mount(from, to, "bind", MS_BIND | MS_REC, NULL) < 0)
errorf(EX_OSERR, "mount"); errorf(EX_OSERR, "mount(%s, %s)", from, to);
} }
char *strjoin(char *dir, char *name) { const char *bind_blacklist[] = {".", "..", "bin", "etc", "host", "usr"};
char *path = malloc(strlen(dir) + strlen(name) + 1);
if (path == NULL) bool str_contains(const char *needle, const char **haystack, size_t len) {
errorf(EX_OSERR, "malloc"); for (size_t i = 0; i < len; i++) {
if (!strcmp(needle, haystack[i]))
if (strcpy(path, dir) < 0)
errorf(EX_IOERR, "strcpy");
if (strcat(path, name) < 0)
errorf(EX_IOERR, "strcat");
return path;
}
char *bind_blacklist[] = {".", "..", "bin", "etc", "host", "usr"};
bool bind_blacklisted(char *name) {
for (size_t i = 0; i < LEN(bind_blacklist); i++) {
if (!strcmp(bind_blacklist[i], name))
return true; return true;
} }
return false; return false;
} }
bool isdir(char *path) { bool is_dir(const char *path) {
struct stat buf; struct stat buf;
stat(path, &buf);
if (stat(path, &buf) < 0)
errorf(EX_IOERR, "stat(%s)", path);
return S_ISDIR(buf.st_mode); return S_ISDIR(buf.st_mode);
} }
void bind_to_cwd(char *prefix) { void bind_to_cwd(const char *prefix) {
DIR *prefix_dir = opendir(prefix); DIR *prefix_dir = opendir(prefix);
if (prefix_dir == NULL) if (prefix_dir == NULL)
errorf(EX_OSERR, "opendir"); errorf(EX_IOERR, "opendir(%s)", prefix);
struct dirent *prefix_dirent; struct dirent *prefix_dirent;
while (prefix_dirent = readdir(prefix_dir)) { while (prefix_dirent = readdir(prefix_dir)) {
if (bind_blacklisted(prefix_dirent->d_name)) if (str_contains(prefix_dirent->d_name, bind_blacklist,
LEN(bind_blacklist)))
continue; continue;
char *prefix_dirent_path = strjoin(prefix, prefix_dirent->d_name); char *prefix_dirent_path;
if (isdir(prefix_dirent_path)) { if (asprintf(&prefix_dirent_path, "%s%s", prefix, prefix_dirent->d_name) <
0)
errorf(EX_IOERR, "asprintf");
if (is_dir(prefix_dirent_path)) {
bind(prefix_dirent_path, prefix_dirent->d_name); bind(prefix_dirent_path, prefix_dirent->d_name);
} else { } else {
char *host_target = strjoin("host/", prefix_dirent->d_name); char *host_target;
if (asprintf(&host_target, "host/%s", prefix_dirent->d_name) < 0)
errorf(EX_IOERR, "asprintf");
if (symlink(host_target, prefix_dirent->d_name) < 0) if (symlink(host_target, prefix_dirent->d_name) < 0)
errorf(EX_IOERR, "symlink"); errorf(EX_IOERR, "symlink(%s, %s)", host_target, prefix_dirent->d_name);
free(host_target); free(host_target);
} }
@ -126,10 +100,10 @@ void bind_to_cwd(char *prefix) {
bind(prefix, "host"); bind(prefix, "host");
if (closedir(prefix_dir) < 0) if (closedir(prefix_dir) < 0)
errorf(EX_IOERR, "closedir"); errorf(EX_IOERR, "closedir(%s)", prefix);
} }
void spitf(char *path, char *fmt, ...) { void spitf(const char *path, char *fmt, ...) {
va_list args; va_list args;
va_start(args, fmt); va_start(args, fmt);
@ -145,41 +119,58 @@ void spitf(char *path, char *fmt, ...) {
errorf(EX_IOERR, "spitf(%s): fclose", path); errorf(EX_IOERR, "spitf(%s): fclose", path);
} }
int nftw_rm(const char *path, const struct stat *sb, int type, int nftw_remove(const char *path, const struct stat *sb, int type,
struct FTW *ftw) { struct FTW *ftw) {
if (remove(path) < 0) return remove(path);
errorf(EX_IOERR, "nftw_rm");
return 0;
} }
#define REQUIREMENTS "Linux version >= 3.19 built with CONFIG_USER_NS option" char *root;
extern char **environ; void root_cleanup() {
if (nftw(root, nftw_remove, getdtablesize(),
FTW_DEPTH | FTW_MOUNT | FTW_PHYS) < 0)
errorf(EX_IOERR, "nftw(%s)", root);
free(root);
}
#define REQUIREMENTS \
"Requires Linux version >= 3.19 built with CONFIG_USER_NS option.\n"
int main(int argc, char *argv[]) { int main(int argc, char *argv[]) {
const char *self = *argv++;
if (argc < 2) { if (argc < 2) {
fprintf(stderr, "Usage: %s command [arguments...]\n" fprintf(stderr, "Usage: %s command [arguments...]\n" REQUIREMENTS, self);
"Requires " REQUIREMENTS ".\n",
argv[0]);
exit(EX_USAGE); exit(EX_USAGE);
} }
if (getenv("NIX_CHROOTENV") != NULL) if (getenv("NIX_CHROOTENV") != NULL) {
errorf(EX_USAGE, "can't create chrootenv inside chrootenv"); fputs("Can't create chrootenv inside chrootenv!\n", stderr);
exit(EX_USAGE);
}
if (setenv("NIX_CHROOTENV", "1", false) < 0) if (setenv("NIX_CHROOTENV", "1", false) < 0)
errorf(EX_IOERR, "setenv"); errorf(EX_OSERR, "setenv(NIX_CHROOTENV, 1)");
char tmpl[] = "/tmp/chrootenvXXXXXX"; const char *temp = getenv("TMPDIR");
char *root = mkdtemp(tmpl);
if (temp == NULL)
temp = "/tmp";
if (asprintf(&root, "%s/chrootenvXXXXXX", temp) < 0)
errorf(EX_IOERR, "asprintf");
root = mkdtemp(root);
if (root == NULL) if (root == NULL)
errorf(EX_IOERR, "mkdtemp"); errorf(EX_IOERR, "mkdtemp(%s)", root);
atexit(root_cleanup);
// Don't make root private so that privilege drops inside chroot are possible: // Don't make root private so that privilege drops inside chroot are possible:
if (chmod(root, 0755) < 0) if (chmod(root, 0755) < 0)
errorf(EX_IOERR, "chmod"); errorf(EX_IOERR, "chmod(%s, 0755)", root);
pid_t cpid = fork(); pid_t cpid = fork();
@ -192,8 +183,10 @@ int main(int argc, char *argv[]) {
// If we are root, no need to create new user namespace. // If we are root, no need to create new user namespace.
if (uid == 0) { if (uid == 0) {
if (unshare(CLONE_NEWNS) < 0) if (unshare(CLONE_NEWNS) < 0) {
errorf(EX_OSERR, "unshare: requires " REQUIREMENTS); fputs(REQUIREMENTS, stderr);
errorf(EX_OSERR, "unshare");
}
// Mark all mounted filesystems as slave so changes // Mark all mounted filesystems as slave so changes
// don't propagate to the parent mount namespace. // don't propagate to the parent mount namespace.
if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0) if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL) < 0)
@ -202,11 +195,11 @@ int main(int argc, char *argv[]) {
// Create new mount and user namespaces. CLONE_NEWUSER // Create new mount and user namespaces. CLONE_NEWUSER
// requires a program to be non-threaded. // requires a program to be non-threaded.
if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) { if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) {
if (access("/tmp/proc/sys/kernel/unprivileged_userns_clone", F_OK) < 0) fputs(access("/proc/sys/kernel/unprivileged_userns_clone", F_OK)
errorf(EX_OSERR, "unshare: requires " REQUIREMENTS); ? REQUIREMENTS
else : "Run: sudo sysctl -w kernel.unprivileged_userns_clone=1\n",
errorf(EX_OSERR, "unshare: run `sudo sysctl -w " stderr);
"kernel.unprivileged_userns_clone=1`"); errorf(EX_OSERR, "unshare");
} }
// Map users and groups to the parent namespace. // Map users and groups to the parent namespace.
@ -218,35 +211,32 @@ int main(int argc, char *argv[]) {
} }
if (chdir(root) < 0) if (chdir(root) < 0)
errorf(EX_IOERR, "chdir"); errorf(EX_IOERR, "chdir(%s)", root);
bind_to_cwd("/"); bind_to_cwd("/");
if (chroot(root) < 0) if (chroot(root) < 0)
errorf(EX_OSERR, "chroot"); errorf(EX_OSERR, "chroot(%s)", root);
if (chdir("/") < 0) if (chdir("/") < 0)
errorf(EX_OSERR, "chdir"); errorf(EX_IOERR, "chdir(/)");
argv++; environ_blacklist_filter();
if (execvpe(*argv, argv, env_filter(environ)) < 0) if (execvp(*argv, argv) < 0)
errorf(EX_OSERR, "execvpe"); errorf(EX_OSERR, "execvp(%s)", *argv);
} }
int status; int status;
if (waitpid(cpid, &status, 0) < 0) if (waitpid(cpid, &status, 0) < 0)
errorf(EX_OSERR, "waitpid"); errorf(EX_OSERR, "waitpid(%d)", cpid);
if (nftw(root, nftw_rm, getdtablesize(), FTW_DEPTH | FTW_MOUNT | FTW_PHYS) < if (WIFEXITED(status)) {
0)
errorf(EX_IOERR, "nftw");
if (WIFEXITED(status))
return WEXITSTATUS(status); return WEXITSTATUS(status);
else if (WIFSIGNALED(status)) } else if (WIFSIGNALED(status)) {
kill(getpid(), WTERMSIG(status)); kill(getpid(), WTERMSIG(status));
}
return EX_OSERR; return EX_OSERR;
} }