JDK14/Java14源码在线阅读
/*
* Copyright (c) 1995, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
#undef _LARGEFILE64_SOURCE
#define _LARGEFILE64_SOURCE 1
#include "jni.h"
#include "jvm.h"
#include "jvm_md.h"
#include "jni_util.h"
#include "io_util.h"
/*
* Platform-specific support for java.lang.Process
*/
#include <assert.h>
#include <stddef.h>
#include <stdlib.h>
#include <sys/types.h>
#include <ctype.h>
#include <sys/wait.h>
#include <signal.h>
#include <string.h>
#include <spawn.h>
#include "childproc.h"
/*
*
* When starting a child on Unix, we need to do three things:
* - fork off
* - in the child process, do some pre-exec work: duping/closing file
* descriptors to set up stdio-redirection, setting environment variables,
* changing paths...
* - then exec(2) the target binary
*
* There are three ways to fork off:
*
* A) fork(2). Portable and safe (no side effects) but may fail with ENOMEM on
* all Unices when invoked from a VM with a high memory footprint. On Unices
* with strict no-overcommit policy this problem is most visible.
*
* This is because forking the VM will first create a child process with
* theoretically the same memory footprint as the parent - even if you plan
* to follow up with exec'ing a tiny binary. In reality techniques like
* copy-on-write etc mitigate the problem somewhat but we still run the risk
* of hitting system limits.
*
* For a Linux centric description of this problem, see the documentation on
* /proc/sys/vm/overcommit_memory in Linux proc(5).
*
* B) vfork(2): Portable and fast but very unsafe. It bypasses the memory
* problems related to fork(2) by starting the child in the memory image of
* the parent. Things that can go wrong include:
* - Programming errors in the child process before the exec(2) call may
* trash memory in the parent process, most commonly the stack of the
* thread invoking vfork.
* - Signals received by the child before the exec(2) call may be at best
* misdirected to the parent, at worst immediately kill child and parent.
*
* This is mitigated by very strict rules about what one is allowed to do in
* the child process between vfork(2) and exec(2), which is basically nothing.
* However, we always broke this rule by doing the pre-exec work between
* vfork(2) and exec(2).
*
* Also note that vfork(2) has been deprecated by the OpenGroup, presumably
* because of its many dangers.
*
* C) clone(2): This is a Linux specific call which gives the caller fine
* grained control about how exactly the process fork is executed. It is
* powerful, but Linux-specific.
*
* Aside from these three possibilities there is a forth option: posix_spawn(3).
* Where fork/vfork/clone all fork off the process and leave pre-exec work and
* calling exec(2) to the user, posix_spawn(3) offers the user fork+exec-like
* functionality in one package, similar to CreateProcess() on Windows.
*
* It is not a system call in itself, but usually a wrapper implemented within
* the libc in terms of one of (fork|vfork|clone)+exec - so whether or not it
* has advantages over calling the naked (fork|vfork|clone) functions depends
* on how posix_spawn(3) is implemented.
*
* Note that when using posix_spawn(3), we exec twice: first a tiny binary called
* the jspawnhelper, then in the jspawnhelper we do the pre-exec work and exec a
* second time, this time the target binary (similar to the "exec-twice-technique"
* described in http://mail.openjdk.java.net/pipermail/core-libs-dev/2018-September/055333.html).
*
* This is a JDK-specific implementation detail which just happens to be
* implemented for jdk.lang.Process.launchMechanism=POSIX_SPAWN.
*
* --- Linux-specific ---
*
* How does glibc implement posix_spawn?
* (see: sysdeps/posix/spawni.c for glibc < 2.24,
* sysdeps/unix/sysv/linux/spawni.c for glibc >= 2.24):
*
* 1) Before glibc 2.4 (released 2006), posix_spawn(3) used just fork(2)/exec(2).
* This would be bad for the JDK since we would risk the known memory issues with
* fork(2). But since this only affects glibc variants which have long been
* phased out by modern distributions, this is irrelevant.
*
* 2) Between glibc 2.4 and glibc 2.23, posix_spawn uses either fork(2) or
* vfork(2) depending on how exactly the user called posix_spawn(3):
*
* <quote>
* The child process is created using vfork(2) instead of fork(2) when
* either of the following is true:
*
* * the spawn-flags element of the attributes object pointed to by
* attrp contains the GNU-specific flag POSIX_SPAWN_USEVFORK; or
*
* * file_actions is NULL and the spawn-flags element of the attributes
* object pointed to by attrp does not contain
* POSIX_SPAWN_SETSIGMASK, POSIX_SPAWN_SETSIGDEF,
* POSIX_SPAWN_SETSCHEDPARAM, POSIX_SPAWN_SETSCHEDULER,
* POSIX_SPAWN_SETPGROUP, or POSIX_SPAWN_RESETIDS.
* </quote>
*
* Due to the way the JDK calls posix_spawn(3), it would therefore call vfork(2).
* So we would avoid the fork(2) memory problems. However, there still remains the
* risk associated with vfork(2). But it is smaller than were we to call vfork(2)
* directly since we use the jspawnhelper, moving all pre-exec work off to after
* the first exec, thereby reducing the vulnerable time window.
*
* 3) Since glibc >= 2.24, glibc uses clone+exec:
*
* new_pid = CLONE (__spawni_child, STACK (stack, stack_size), stack_size,
* CLONE_VM | CLONE_VFORK | SIGCHLD, &args);
*
* This is even better than (2):
*
* CLONE_VM means we run in the parent's memory image, as with (2)
* CLONE_VFORK means parent waits until we exec, as with (2)
*
* However, error possibilities are further reduced since:
* - posix_spawn(3) passes a separate stack for the child to run on, eliminating
* the danger of trashing the forking thread's stack in the parent process.
* - posix_spawn(3) takes care to temporarily block all incoming signals to the
* child process until the first exec(2) has been called,
*
* TL;DR
* Calling posix_spawn(3) for glibc
* (2) < 2.24 is not perfect but still better than using plain vfork(2), since
* the chance of an error happening is greatly reduced
* (3) >= 2.24 is the best option - portable, fast and as safe as possible.
*
* ---
*
* How does muslc implement posix_spawn?
*
* They always did use the clone (.. CLONE_VM | CLONE_VFORK ...)
* technique. So we are safe to use posix_spawn() here regardless of muslc
* version.
*
* </Linux-specific>
*
*
* Based on the above analysis, we are currently defaulting to posix_spawn()
* on all Unices including Linux.
*/
static void
setSIGCHLDHandler(JNIEnv *env)
{
/* There is a subtle difference between having the signal handler
* for SIGCHLD be SIG_DFL and SIG_IGN. We cannot obtain process
* termination information for child processes if the signal
* handler is SIG_IGN. It must be SIG_DFL.
*
* We used to set the SIGCHLD handler only on Linux, but it's
* safest to set it unconditionally.
*
* Consider what happens if java's parent process sets the SIGCHLD
* handler to SIG_IGN. Normally signal handlers are inherited by
* children, but SIGCHLD is a controversial case. Solaris appears
* to always reset it to SIG_DFL, but this behavior may be
* non-standard-compliant, and we shouldn't rely on it.
*
* References:
* http://www.opengroup.org/onlinepubs/7908799/xsh/exec.html
* http://www.pasc.org/interps/unofficial/db/p1003.1/pasc-1003.1-132.html
*/
struct sigaction sa;
sa.sa_handler = SIG_DFL;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) < 0)
JNU_ThrowInternalError(env, "Can't set SIGCHLD handler");
}
static void*
xmalloc(JNIEnv *env, size_t size)
{
void *p = malloc(size);
if (p == NULL)
JNU_ThrowOutOfMemoryError(env, NULL);
return p;
}
#define NEW(type, n) ((type *) xmalloc(env, (n) * sizeof(type)))
/**
* If PATH is not defined, the OS provides some default value.
* Unfortunately, there's no portable way to get this value.
* Fortunately, it's only needed if the child has PATH while we do not.
*/
static const char*
defaultPath(void)
{
#ifdef __solaris__
/* These really are the Solaris defaults! */
return (geteuid() == 0 || getuid() == 0) ?
"/usr/xpg4/bin:/usr/bin:/opt/SUNWspro/bin:/usr/sbin" :
"/usr/xpg4/bin:/usr/bin:/opt/SUNWspro/bin:";
#else
return ":/bin:/usr/bin"; /* glibc */
#endif
}
static const char*
effectivePath(void)
{
const char *s = getenv("PATH");
return (s != NULL) ? s : defaultPath();
}
static int
countOccurrences(const char *s, char c)
{
int count;
for (count = 0; *s != '\0'; s++)
count += (*s == c);
return count;
}
static const char * const *
effectivePathv(JNIEnv *env)
{
char *p;
int i;
const char *path = effectivePath();
int count = countOccurrences(path, ':') + 1;
size_t pathvsize = sizeof(const char *) * (count+1);
size_t pathsize = strlen(path) + 1;
const char **pathv = (const char **) xmalloc(env, pathvsize + pathsize);
if (pathv == NULL)
return NULL;
p = (char *) pathv + pathvsize;
memcpy(p, path, pathsize);
/* split PATH by replacing ':' with NULs; empty components => "." */
for (i = 0; i < count; i++) {
char *q = p + strcspn(p, ":");
pathv[i] = (p == q) ? "." : p;
*q = '\0';
p = q + 1;
}
pathv[count] = NULL;
return pathv;
}
JNIEXPORT void JNICALL
Java_java_lang_ProcessImpl_init(JNIEnv *env, jclass clazz)
{
parentPathv = effectivePathv(env);
CHECK_NULL(parentPathv);
setSIGCHLDHandler(env);
}
#ifndef WIFEXITED
#define WIFEXITED(status) (((status)&0xFF) == 0)
#endif
#ifndef WEXITSTATUS
#define WEXITSTATUS(status) (((status)>>8)&0xFF)
#endif
#ifndef WIFSIGNALED
#define WIFSIGNALED(status) (((status)&0xFF) > 0 && ((status)&0xFF00) == 0)
#endif
#ifndef WTERMSIG
#define WTERMSIG(status) ((status)&0x7F)
#endif
static const char *
getBytes(JNIEnv *env, jbyteArray arr)
{
return arr == NULL ? NULL :
(const char*) (*env)->GetByteArrayElements(env, arr, NULL);
}
static void
releaseBytes(JNIEnv *env, jbyteArray arr, const char* parr)
{
if (parr != NULL)
(*env)->ReleaseByteArrayElements(env, arr, (jbyte*) parr, JNI_ABORT);
}
#define IOE_FORMAT "error=%d, %s"
static void
throwIOException(JNIEnv *env, int errnum, const char *defaultDetail)
{
const char *detail = defaultDetail;
char *errmsg;
size_t fmtsize;
char tmpbuf[1024];
jstring s;
if (errnum != 0) {
int ret = getErrorString(errnum, tmpbuf, sizeof(tmpbuf));
if (ret != EINVAL)
detail = tmpbuf;
}
/* ASCII Decimal representation uses 2.4 times as many bits as binary. */
fmtsize = sizeof(IOE_FORMAT) + strlen(detail) + 3 * sizeof(errnum);
errmsg = NEW(char, fmtsize);
if (errmsg == NULL)
return;
snprintf(errmsg, fmtsize, IOE_FORMAT, errnum, detail);
s = JNU_NewStringPlatform(env, errmsg);
if (s != NULL) {
jobject x = JNU_NewObjectByName(env, "java/io/IOException",
"(Ljava/lang/String;)V", s);
if (x != NULL)
(*env)->Throw(env, x);
}
free(errmsg);
}
/**
* Throws an IOException with a message composed from the result of waitpid status.
*/
static void throwExitCause(JNIEnv *env, int pid, int status) {
char ebuf[128];
if (WIFEXITED(status)) {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, exit value: %d",
pid, WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, signal: %d",
pid, WTERMSIG(status));
} else {
snprintf(ebuf, sizeof ebuf,
"Failed to exec spawn helper: pid: %d, status: 0x%08x",
pid, status);
}
throwIOException(env, 0, ebuf);
}
#ifdef DEBUG_PROCESS
/* Debugging process code is difficult; where to write debug output? */
static void
debugPrint(char *format, ...)
{
FILE *tty = fopen("/dev/tty", "w");
va_list ap;
va_start(ap, format);
vfprintf(tty, format, ap);
va_end(ap);
fclose(tty);
}
#endif /* DEBUG_PROCESS */
static void
copyPipe(int from[2], int to[2])
{
to[0] = from[0];
to[1] = from[1];
}
/* arg is an array of pointers to 0 terminated strings. array is terminated
* by a null element.
*
* *nelems and *nbytes receive the number of elements of array (incl 0)
* and total number of bytes (incl. 0)
* Note. An empty array will have one null element
* But if arg is null, then *nelems set to 0, and *nbytes to 0
*/
static void arraysize(const char * const *arg, int *nelems, int *nbytes)
{
int i, bytes, count;
const char * const *a = arg;
char *p;
int *q;
if (arg == 0) {
*nelems = 0;
*nbytes = 0;
return;
}
/* count the array elements and number of bytes */
for (count=0, bytes=0; *a != 0; count++, a++) {
bytes += strlen(*a)+1;
}
*nbytes = bytes;
*nelems = count+1;
}
/* copy the strings from arg[] into buf, starting at given offset
* return new offset to next free byte
*/
static int copystrings(char *buf, int offset, const char * const *arg) {
char *p;
const char * const *a;
int count=0;
if (arg == 0) {
return offset;
}
for (p=buf+offset, a=arg; *a != 0; a++) {
int len = strlen(*a) +1;
memcpy(p, *a, len);
p += len;
count += len;
}
return offset+count;
}
/**
* We are unusually paranoid; use of vfork is
* especially likely to tickle gcc/glibc bugs.
*/
#ifdef __attribute_noinline__ /* See: sys/cdefs.h */
__attribute_noinline__
#endif
/* vfork(2) is deprecated on Solaris */
#ifndef __solaris__
static pid_t
vforkChild(ChildStuff *c) {
volatile pid_t resultPid;
/*
* We separate the call to vfork into a separate function to make
* very sure to keep stack of child from corrupting stack of parent,
* as suggested by the scary gcc warning:
* warning: variable 'foo' might be clobbered by 'longjmp' or 'vfork'
*/
resultPid = vfork();
if (resultPid == 0) {
childProcess(c);
}
assert(resultPid != 0); /* childProcess never returns */
return resultPid;
}
#endif
static pid_t
forkChild(ChildStuff *c) {
pid_t resultPid;
/*
* From Solaris fork(2): In Solaris 10, a call to fork() is
* identical to a call to fork1(); only the calling thread is
* replicated in the child process. This is the POSIX-specified
* behavior for fork().
*/
resultPid = fork();
if (resultPid == 0) {
childProcess(c);
}
assert(resultPid != 0); /* childProcess never returns */
return resultPid;
}
static pid_t
spawnChild(JNIEnv *env, jobject process, ChildStuff *c, const char *helperpath) {
pid_t resultPid;
jboolean isCopy;
int i, offset, rval, bufsize, magic;
char *buf, buf1[16];
char *hlpargs[2];
SpawnInfo sp;
/* need to tell helper which fd is for receiving the childstuff
* and which fd to send response back on
*/
snprintf(buf1, sizeof(buf1), "%d:%d", c->childenv[0], c->fail[1]);
/* put the fd string as argument to the helper cmd */
hlpargs[0] = buf1;
hlpargs[1] = 0;
/* Following items are sent down the pipe to the helper
* after it is spawned.
* All strings are null terminated. All arrays of strings
* have an empty string for termination.
* - the ChildStuff struct
* - the SpawnInfo struct
* - the argv strings array
* - the envv strings array
* - the home directory string
* - the parentPath string
* - the parentPathv array
*/
/* First calculate the sizes */
arraysize(c->argv, &sp.nargv, &sp.argvBytes);
bufsize = sp.argvBytes;
arraysize(c->envv, &sp.nenvv, &sp.envvBytes);
bufsize += sp.envvBytes;
sp.dirlen = c->pdir == 0 ? 0 : strlen(c->pdir)+1;
bufsize += sp.dirlen;
arraysize(parentPathv, &sp.nparentPathv, &sp.parentPathvBytes);
bufsize += sp.parentPathvBytes;
/* We need to clear FD_CLOEXEC if set in the fds[].
* Files are created FD_CLOEXEC in Java.
* Otherwise, they will be closed when the target gets exec'd */
for (i=0; i<3; i++) {
if (c->fds[i] != -1) {
int flags = fcntl(c->fds[i], F_GETFD);
if (flags & FD_CLOEXEC) {
fcntl(c->fds[i], F_SETFD, flags & (~1));
}
}
}
rval = posix_spawn(&resultPid, helperpath, 0, 0, (char * const *) hlpargs, environ);
if (rval != 0) {
return -1;
}
/* now the lengths are known, copy the data */
buf = NEW(char, bufsize);
if (buf == 0) {
return -1;
}
offset = copystrings(buf, 0, &c->argv[0]);
offset = copystrings(buf, offset, &c->envv[0]);
memcpy(buf+offset, c->pdir, sp.dirlen);
offset += sp.dirlen;
offset = copystrings(buf, offset, parentPathv);
assert(offset == bufsize);
magic = magicNumber();
/* write the two structs and the data buffer */
write(c->childenv[1], (char *)&magic, sizeof(magic)); // magic number first
write(c->childenv[1], (char *)c, sizeof(*c));
write(c->childenv[1], (char *)&sp, sizeof(sp));
write(c->childenv[1], buf, bufsize);
free(buf);
/* In this mode an external main() in invoked which calls back into
* childProcess() in this file, rather than directly
* via the statement below */
return resultPid;
}
/*
* Start a child process running function childProcess.
* This function only returns in the parent.
*/
static pid_t
startChild(JNIEnv *env, jobject process, ChildStuff *c, const char *helperpath) {
switch (c->mode) {
/* vfork(2) is deprecated on Solaris */
#ifndef __solaris__
case MODE_VFORK:
return vforkChild(c);
#endif
case MODE_FORK:
return forkChild(c);
case MODE_POSIX_SPAWN:
return spawnChild(env, process, c, helperpath);
default:
return -1;
}
}
JNIEXPORT jint JNICALL
Java_java_lang_ProcessImpl_forkAndExec(JNIEnv *env,
jobject process,
jint mode,
jbyteArray helperpath,
jbyteArray prog,
jbyteArray argBlock, jint argc,
jbyteArray envBlock, jint envc,
jbyteArray dir,
jintArray std_fds,
jboolean redirectErrorStream)
{
int errnum;
int resultPid = -1;
int in[2], out[2], err[2], fail[2], childenv[2];
jint *fds = NULL;
const char *phelperpath = NULL;
const char *pprog = NULL;
const char *pargBlock = NULL;
const char *penvBlock = NULL;
ChildStuff *c;
in[0] = in[1] = out[0] = out[1] = err[0] = err[1] = fail[0] = fail[1] = -1;
childenv[0] = childenv[1] = -1;
if ((c = NEW(ChildStuff, 1)) == NULL) return -1;
c->argv = NULL;
c->envv = NULL;
c->pdir = NULL;
/* Convert prog + argBlock into a char ** argv.
* Add one word room for expansion of argv for use by
* execve_as_traditional_shell_script.
* This word is also used when using posix_spawn mode
*/
assert(prog != NULL && argBlock != NULL);
if ((phelperpath = getBytes(env, helperpath)) == NULL) goto Catch;
if ((pprog = getBytes(env, prog)) == NULL) goto Catch;
if ((pargBlock = getBytes(env, argBlock)) == NULL) goto Catch;
if ((c->argv = NEW(const char *, argc + 3)) == NULL) goto Catch;
c->argv[0] = pprog;
c->argc = argc + 2;
initVectorFromBlock(c->argv+1, pargBlock, argc);
if (envBlock != NULL) {
/* Convert envBlock into a char ** envv */
if ((penvBlock = getBytes(env, envBlock)) == NULL) goto Catch;
if ((c->envv = NEW(const char *, envc + 1)) == NULL) goto Catch;
initVectorFromBlock(c->envv, penvBlock, envc);
}
if (dir != NULL) {
if ((c->pdir = getBytes(env, dir)) == NULL) goto Catch;
}
assert(std_fds != NULL);
fds = (*env)->GetIntArrayElements(env, std_fds, NULL);
if (fds == NULL) goto Catch;
if ((fds[0] == -1 && pipe(in) < 0) ||
(fds[1] == -1 && pipe(out) < 0) ||
(fds[2] == -1 && pipe(err) < 0) ||
(pipe(childenv) < 0) ||
(pipe(fail) < 0)) {
throwIOException(env, errno, "Bad file descriptor");
goto Catch;
}
c->fds[0] = fds[0];
c->fds[1] = fds[1];
c->fds[2] = fds[2];
copyPipe(in, c->in);
copyPipe(out, c->out);
copyPipe(err, c->err);
copyPipe(fail, c->fail);
copyPipe(childenv, c->childenv);
c->redirectErrorStream = redirectErrorStream;
c->mode = mode;
/* In posix_spawn mode, require the child process to signal aliveness
* right after it comes up. This is because there are implementations of
* posix_spawn() which do not report failed exec()s back to the caller
* (e.g. glibc, see JDK-8223777). In those cases, the fork() will have
* worked and successfully started the child process, but the exec() will
* have failed. There is no way for us to distinguish this from a target
* binary just exiting right after start.
*
* Note that we could do this additional handshake in all modes but for
* prudence only do it when it is needed (in posix_spawn mode). */
c->sendAlivePing = (mode == MODE_POSIX_SPAWN) ? 1 : 0;
resultPid = startChild(env, process, c, phelperpath);
assert(resultPid != 0);
if (resultPid < 0) {
switch (c->mode) {
case MODE_VFORK:
throwIOException(env, errno, "vfork failed");
break;
case MODE_FORK:
throwIOException(env, errno, "fork failed");
break;
case MODE_POSIX_SPAWN:
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