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scriptd: Use posix_spawn rather than fork/exec.

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Also don't bother providing an artificial environment.
This commit is contained in:
Nicholas J. Kain 2022-08-09 13:40:10 -04:00
parent 45e8e0bad2
commit 898765e0a8
6 changed files with 162 additions and 230 deletions
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193
nk/exec.c
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@ -1,193 +0,0 @@
// Copyright 2003-2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#include <sys/types.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <limits.h>
#include <pwd.h>
#include "nk/stb_sprintf.h"
#include "nk/exec.h"
#include "nk/io.h"
/*
* Note that nk_generate_env is not async signal safe if chroot_path is not
* NULL, so it should only be called after fork() in a non-multithreaded
* process if chroot_path is ever non-NULL.
*
* I don't consider this to be a problem in general, since in a multithreaded process
* it would be far better to fork off a subprocess early on before threads are
* created and use a socketpair() to request subprocess creation from the
* single-threaded subprocess from the multithreaded main program.
*/
#define DEFAULT_ROOT_PATH "/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin"
#define DEFAULT_PATH "/bin:/usr/bin:/usr/local/bin"
#define MAX_ARGS 256
#define MAX_ARGBUF 16384
#define MAX_PWBUF 16384
#define NK_GEN_ENV(GEN_STR, ...) do { \
if (env_offset >= envlen) return -3; \
ssize_t snlen = stbsp_snprintf(envbuf, envbuflen, GEN_STR, __VA_ARGS__); \
if (snlen < 0 || (size_t)snlen > envbuflen) return -2; \
xe->env[env_offset++] = envbuf; envbuf += snlen; envbuflen -= (size_t)snlen; \
} while (0)
/*
* xe: contains generated env and backing buffer
* uid: userid of the user account that the environment will constructed for
* chroot_path: path where the environment will be chrooted or NULL if no chroot
* path_var: value of the PATH variable in the environment or defaults if NULL
*
* returns:
* 0 on success
* -1 if an account for uid does not exist
* -2 if there is not enough space in envbuf for the generated environment
* -3 if there is not enough space in env for the generated environment
* -4 if chdir to homedir or rootdir failed
* -5 if oom or i/o failed
* -6 if MAX_PWBUF is too small
*/
int nk_generate_env(struct nk_exec_env *xe, uid_t uid, const char *chroot_path, const char *path_var)
{
char pwbuf[MAX_PWBUF];
struct passwd pw_s, *pw;
for (;;) {
int r = getpwuid_r(uid, &pw_s, pwbuf, sizeof pwbuf, &pw);
if (!r) {
if (pw == NULL) return -1;
break;
} else {
if (r == EINTR) continue;
if (r == ERANGE) return -6;
return -5;
}
}
size_t env_offset = 0;
size_t envlen = sizeof xe->env / sizeof xe->env[0];
char *envbuf = xe->envbuf;
size_t envbuflen = sizeof xe->envbuf;
if (envlen-- < 1) return -3; // So we don't have to account for the terminal NULL
NK_GEN_ENV("UID=%i", uid);
NK_GEN_ENV("USER=%s", pw->pw_name);
NK_GEN_ENV("USERNAME=%s", pw->pw_name);
NK_GEN_ENV("LOGNAME=%s", pw->pw_name);
NK_GEN_ENV("HOME=%s", pw->pw_dir);
NK_GEN_ENV("SHELL=%s", pw->pw_shell);
NK_GEN_ENV("PATH=%s", path_var ? path_var : (uid > 0 ? DEFAULT_PATH : DEFAULT_ROOT_PATH));
NK_GEN_ENV("PWD=%s", !chroot_path ? pw->pw_dir : "/");
if (chroot_path && chroot(chroot_path)) return -4;
if (chdir(chroot_path ? chroot_path : "/")) return -4;
xe->env[env_offset] = 0;
return 0;
}
#define ERRSTR0 "exec: failed to generate environment - (?) unknown error\n"
#define ERRSTR1 "exec: failed to generate environment - (-1) account for uid does not exist\n"
#define ERRSTR2 "exec: failed to generate environment - (-2) not enough space in envbuf\n"
#define ERRSTR3 "exec: failed to generate environment - (-3) not enough space in env\n"
#define ERRSTR4 "exec: failed to generate environment - (-4) chdir to homedir or rootdir failed\n"
#define ERRSTR5 "exec: failed to generate environment - (-5) oom or i/o error\n"
#define ERRSTR6 "exec: failed to generate environment - (-6) MAX_PWBUF is too small\n"
void nk_generate_env_print_error(int err)
{
switch (err) {
default: safe_write(STDERR_FILENO, ERRSTR0, sizeof ERRSTR0); break;
case -1: safe_write(STDERR_FILENO, ERRSTR1, sizeof ERRSTR1); break;
case -2: safe_write(STDERR_FILENO, ERRSTR2, sizeof ERRSTR2); break;
case -3: safe_write(STDERR_FILENO, ERRSTR3, sizeof ERRSTR3); break;
case -4: safe_write(STDERR_FILENO, ERRSTR4, sizeof ERRSTR4); break;
case -5: safe_write(STDERR_FILENO, ERRSTR5, sizeof ERRSTR5); break;
case -6: safe_write(STDERR_FILENO, ERRSTR6, sizeof ERRSTR6); break;
}
}
#undef ERRSTR0
#undef ERRSTR1
#undef ERRSTR2
#undef ERRSTR3
#undef ERRSTR4
#undef ERRSTR5
#undef ERRSTR6
#define NK_GEN_ARG(GEN_STR, ...) do { \
ssize_t snlen = stbsp_snprintf(argbuf, argbuflen, GEN_STR, __VA_ARGS__); \
if (snlen < 0 || (size_t)snlen > argbuflen) { \
static const char errstr[] = "nk_execute: constructing argument list failed\n"; \
safe_write(STDERR_FILENO, errstr, sizeof errstr); \
_Exit(EXIT_FAILURE); \
} \
argv[curv] = argbuf; argv[++curv] = NULL; \
argbuf += snlen; argbuflen -= (size_t)snlen; \
} while (0)
void __attribute__((noreturn))
nk_execute(const char *command, const char *args, char * const envp[])
{
char *argv[MAX_ARGS];
char argbuf_s[MAX_ARGBUF];
char *argbuf = argbuf_s;
size_t curv = 0;
size_t argbuflen = sizeof argbuf_s;
if (!command)
_Exit(EXIT_SUCCESS);
// strip the path from the command name and set argv[0]
const char *p = strrchr(command, '/');
NK_GEN_ARG("%s", p ? p + 1 : command);
if (args) {
p = args;
const char *q = args;
bool squote = false, dquote = false, atend = false;
for (;; ++p) {
switch (*p) {
default: continue;
case '\0':
atend = true;
goto endarg;
case ' ':
if (!squote && !dquote)
goto endarg;
continue;
case '\'':
if (!dquote)
squote = !squote;
continue;
case '"':
if (!squote)
dquote = !dquote;
continue;
}
endarg:
{
if (p == q) break;
// Push an argument.
if (q > p) {
static const char errstr[] = "nk_execute: argument length too long\n";
safe_write(STDERR_FILENO, errstr, sizeof errstr);
_Exit(EXIT_FAILURE);
}
NK_GEN_ARG("%.*s", (int)(p - q), q);
q = p + 1;
if (atend || curv >= (MAX_ARGS - 1))
break;
}
}
}
execve(command, argv, envp);
{
static const char errstr[] = "nk_execute: execve failed\n";
safe_write(STDERR_FILENO, errstr, sizeof errstr);
_Exit(EXIT_FAILURE);
}
}

19
nk/exec.h
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@ -1,19 +0,0 @@
// Copyright 2003-2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#ifndef NCM_EXEC_H_
#define NCM_EXEC_H_
struct nk_exec_env
{
char *env[32];
char envbuf[4096];
};
int nk_generate_env(struct nk_exec_env *xe, uid_t uid, const char *chroot_path, const char *path_var);
void nk_generate_env_print_error(int err);
void __attribute__((noreturn))
nk_execute(const char *command, const char *args, char * const envp[]) ;
#endif

52
nk/nstrcpy.h Normal file
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@ -0,0 +1,52 @@
#ifndef NKLIB_NSTRCPY_H_
#define NKLIB_NSTRCPY_H_
#include <stddef.h>
#include <string.h>
// Returns pointer to end of dest string (NULL terminator) if
// src is not truncated when copying to dest.
// Otherwise, returns NULL if src is truncated or size == 0.
static inline char *nstrcpy(char *dest, size_t size, const char *src)
{
if (!size) return NULL;
char c;
for (size_t i = 0; i < size; ++i, ++dest) {
c = *src++;
*dest = c;
if (!c) return dest;
}
*(dest - 1) = 0;
return NULL;
}
// Same semantics as above, except we append to dest.
static inline char *nstrcat(char *dest, size_t size, const char *src)
{
size_t len = strlen(dest);
return nstrcpy(dest + len, size - len, src);
}
// Acts as nstrcpy, but does not require src to be NULL terminated.
// That said, it will stop early if src contains a NULL terminator.
static inline char *nstrcpyl(char *dest, size_t dsize, const char *src, size_t ssize)
{
if (!dsize) return NULL;
char c;
size_t i = 0, j = 0;
for (; i < dsize && j < ssize; ++i, ++j, ++dest) {
c = *src++;
*dest = c;
if (!c) return dest;
}
if (i == dsize) {
*(dest - 1) = 0;
return NULL;
}
// j == ssize here
*dest = 0;
return dest;
}
#endif

90
nk/pspawn.c Normal file
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@ -0,0 +1,90 @@
// Copyright 2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#include <sys/types.h>
#include <stdbool.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include "nk/nstrcpy.h"
#include "nk/pspawn.h"
#include "nk/io.h"
#define MAX_ARGS 256
#define MAX_ARGBUF 16384
#define NK_GEN_ARG(STRVAL, STRLEN) do { \
char *snp = nstrcpyl(argbuf, argbuflen, STRVAL, STRLEN); \
if (!snp) { \
static const char errstr[] = "nk_pspawn: constructing argument list failed\n"; \
safe_write(STDERR_FILENO, errstr, sizeof errstr); \
_Exit(EXIT_FAILURE); \
} \
argv[curv] = argbuf; argv[++curv] = NULL; \
size_t l = (size_t)(snp - argbuf); \
argbuf += l; argbuflen -= l; \
} while (0)
int nk_pspawn(pid_t *pid, const char *command,
const posix_spawn_file_actions_t *restrict file_actions,
const posix_spawnattr_t *restrict attrp,
const char *args, char * const envp[])
{
char *argv[MAX_ARGS];
char argbuf_s[MAX_ARGBUF];
char *argbuf = argbuf_s;
size_t curv = 0;
size_t argbuflen = sizeof argbuf_s;
if (!command)
_Exit(EXIT_SUCCESS);
// strip the path from the command name and set argv[0]
const char *p = strrchr(command, '/');
{
const char *q = p ? p + 1 : command;
size_t ql = strlen(q);
NK_GEN_ARG(q, ql);
}
if (args) {
p = args;
const char *q = args;
bool squote = false, dquote = false, atend = false;
for (;; ++p) {
switch (*p) {
default: continue;
case '\0':
atend = true;
goto endarg;
case ' ':
if (!squote && !dquote)
goto endarg;
continue;
case '\'':
if (!dquote)
squote = !squote;
continue;
case '"':
if (!squote)
dquote = !dquote;
continue;
}
endarg:
{
if (p == q) break;
// Push an argument.
if (q > p) {
static const char errstr[] = "nk_execute: argument length too long\n";
safe_write(STDERR_FILENO, errstr, sizeof errstr);
_Exit(EXIT_FAILURE);
}
NK_GEN_ARG(q, (size_t)(p - q));
q = p + 1;
if (atend || curv >= (MAX_ARGS - 1))
break;
}
}
}
return posix_spawn(pid, command, file_actions, attrp, argv, envp);
}

15
nk/pspawn.h Normal file
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@ -0,0 +1,15 @@
// Copyright 2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#ifndef NCM_PSPAWN_H_
#define NCM_PSPAWN_H_
#include <sys/types.h>
#include <spawn.h>
int nk_pspawn(pid_t *pid, const char *command,
const posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *attrp,
const char *args, char * const envp[]);
#endif

23
scriptd.c
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@ -12,11 +12,12 @@
#include <sys/stat.h>
#include "nk/log.h"
#include "nk/io.h"
#include "nk/exec.h"
#include "nk/pspawn.h"
#include "scriptd.h"
#include "ndhc.h"
#include "sys.h"
extern char **environ;
bool valid_script_file = false;
// Runs the 'script_file'-specified script. Called from ndhc process.
@ -33,23 +34,9 @@ void request_scriptd_run(void)
static void run_script(void)
{
struct nk_exec_env xe;
switch ((int)fork()) {
case 0: {
int r = nk_generate_env(&xe, 0, NULL, NULL);
if (r < 0) {
nk_generate_env_print_error(r);
exit(EXIT_FAILURE);
}
nk_execute(script_file, NULL, xe.env);
}
case -1: {
static const char errstr[] = "exec: fork failed\n";
safe_write(STDERR_FILENO, errstr, sizeof errstr);
exit(EXIT_FAILURE);
}
default: break;
}
pid_t pid;
int ret = nk_pspawn(&pid, script_file, NULL, NULL, NULL, environ);
if (ret) log_line("posix_spawn failed for '%s': %s\n", script_file, strerror(ret));
}
static void process_client_socket(void)