From b4220fce04a3cbe2e8c309ab8845fbd6fac631a5 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Fri, 26 Jan 2018 16:34:59 +0100 Subject: [PATCH 1/3] mingw: demonstrate that all file handles are inherited by child processes When spawning child processes, we really should be careful which file handles we let them inherit. This is doubly important on Windows, where we cannot rename, delete, or modify files if there is still a file handle open. Sadly, we have to guard this test inside #ifdef WIN32: we need to use the value of the HANDLE directly, and that concept does not exist on Linux/Unix. Signed-off-by: Johannes Schindelin --- t/helper/test-run-command.c | 47 +++++++++++++++++++++++++++++++++++++ t/t0061-run-command.sh | 4 ++++ 2 files changed, 51 insertions(+) diff --git a/t/helper/test-run-command.c b/t/helper/test-run-command.c index 2cc93bb69c..e1bc58b956 100644 --- a/t/helper/test-run-command.c +++ b/t/helper/test-run-command.c @@ -50,11 +50,58 @@ static int task_finished(int result, return 1; } +static int inherit_handle(const char *argv0) +{ + struct child_process cp = CHILD_PROCESS_INIT; + char path[PATH_MAX]; + int tmp; + + /* First, open an inheritable handle */ + xsnprintf(path, sizeof(path), "out-XXXXXX"); + tmp = xmkstemp(path); + + argv_array_pushl(&cp.args, + "test-tool", argv0, "inherited-handle-child", NULL); + cp.in = -1; + cp.no_stdout = cp.no_stderr = 1; + if (start_command(&cp) < 0) + die("Could not start child process"); + + /* Then close it, and try to delete it. */ + close(tmp); + if (unlink(path)) + die("Could not delete '%s'", path); + + if (close(cp.in) < 0 || finish_command(&cp) < 0) + die("Child did not finish"); + + return 0; +} + +static int inherit_handle_child(void) +{ + struct strbuf buf = STRBUF_INIT; + + if (strbuf_read(&buf, 0, 0) < 0) + die("Could not read stdin"); + printf("Received %s\n", buf.buf); + strbuf_release(&buf); + + return 0; +} + int cmd__run_command(int argc, const char **argv) { struct child_process proc = CHILD_PROCESS_INIT; int jobs; + if (argc < 2) + return 1; + if (!strcmp(argv[1], "inherited-handle")) + exit(inherit_handle(argv[0])); + if (!strcmp(argv[1], "inherited-handle-child")) + exit(inherit_handle_child()); + if (argc < 3) return 1; while (!strcmp(argv[1], "env")) { diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh index 3e131c5325..d800c0a4d1 100755 --- a/t/t0061-run-command.sh +++ b/t/t0061-run-command.sh @@ -12,6 +12,10 @@ cat >hello-script <<-EOF cat hello-script EOF +test_expect_failure MINGW 'subprocess inherits only std handles' ' + test-tool run-command inherited-handle +' + test_expect_success 'start_command reports ENOENT' ' test-tool run-command start-command-ENOENT ./does-not-exist ' From faa912625a6cc23082b40e868b46103aae9c5a6d Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Wed, 7 Feb 2018 13:50:03 +0100 Subject: [PATCH 2/3] mingw: work around incorrect standard handles For some reason, when being called via TortoiseGit the standard handles, or at least what is returned by _get_osfhandle(0) for standard input, can take on the value (HANDLE)-2 (which is not a legal value, according to the documentation). Even if this value is not documented anywhere, CreateProcess() seems to work fine without complaints if hStdInput set to this value. In contrast, the upcoming code to restrict which file handles get inherited by spawned processes would result in `ERROR_INVALID_PARAMETER` when including such handle values in the list. To help this, special-case the value (HANDLE)-2 returned by _get_osfhandle() and replace it with INVALID_HANDLE_VALUE, which will hopefully let the handle inheritance restriction work even when called from TortoiseGit. This fixes https://github.com/git-for-windows/git/issues/1481 Signed-off-by: Johannes Schindelin --- compat/winansi.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/compat/winansi.c b/compat/winansi.c index a11a0f16d2..f5dcc8de70 100644 --- a/compat/winansi.c +++ b/compat/winansi.c @@ -639,10 +639,20 @@ void winansi_init(void) */ HANDLE winansi_get_osfhandle(int fd) { + HANDLE ret; + if (fd == 1 && (fd_is_interactive[1] & FD_SWAPPED)) return hconsole1; if (fd == 2 && (fd_is_interactive[2] & FD_SWAPPED)) return hconsole2; - return (HANDLE)_get_osfhandle(fd); + ret = (HANDLE)_get_osfhandle(fd); + + /* + * There are obviously circumstances under which _get_osfhandle() + * returns (HANDLE)-2. This is not documented anywhere, but that is so + * clearly an invalid handle value that we can just work around this + * and return the correct value for invalid handles. + */ + return ret == (HANDLE)-2 ? INVALID_HANDLE_VALUE : ret; } From f28481bb7fb7284554a1deebe84117087ddb6992 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Fri, 26 Jan 2018 15:37:38 +0100 Subject: [PATCH 3/3] mingw: spawned processes need to inherit only standard handles By default, CreateProcess() does not inherit any open file handles, unless the bInheritHandles parameter is set to TRUE. Which we do need to set because we need to pass in stdin/stdout/stderr to talk to the child processes. Sadly, this means that all file handles (unless marked via O_NOINHERIT) are inherited. This lead to problems in GVFS Git, where a long-running read-object hook is used to hydrate missing objects, and depending on the circumstances, might only be called *after* Git opened a file handle. Ideally, we would not open files without O_NOINHERIT unless *really* necessary (i.e. when we want to pass the opened file handle as standard handle into a child process), but apparently it is all-too-easy to introduce incorrect open() calls: this happened, and prevented updating a file after the read-object hook was started because the hook still held a handle on said file. Happily, there is a solution: as described in the "Old New Thing" https://blogs.msdn.microsoft.com/oldnewthing/20111216-00/?p=8873 there is a way, starting with Windows Vista, that lets us define precisely which handles should be inherited by the child process. And since we bumped the minimum Windows version for use with Git for Windows to Vista with v2.10.1 (i.e. a *long* time ago), we can use this method. So let's do exactly that. We need to make sure that the list of handles to inherit does not contain duplicates; Otherwise CreateProcessW() would fail with ERROR_INVALID_ARGUMENT. While at it, stop setting errno to ENOENT unless it really is the correct value. Also, fall back to not limiting handle inheritance under certain error conditions (e.g. on Windows 7, which is a lot stricter in what handles you can specify to limit to). Signed-off-by: Johannes Schindelin --- compat/mingw.c | 120 +++++++++++++++++++++++++++++++++++++---- t/t0061-run-command.sh | 2 +- 2 files changed, 110 insertions(+), 12 deletions(-) diff --git a/compat/mingw.c b/compat/mingw.c index e5f21fefe2..869765d2a8 100644 --- a/compat/mingw.c +++ b/compat/mingw.c @@ -1371,8 +1371,13 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen const char *dir, int prepend_cmd, int fhin, int fhout, int fherr) { - STARTUPINFOW si; + static int restrict_handle_inheritance = 1; + STARTUPINFOEXW si; PROCESS_INFORMATION pi; + LPPROC_THREAD_ATTRIBUTE_LIST attr_list = NULL; + HANDLE stdhandles[3]; + DWORD stdhandles_count = 0; + SIZE_T size; struct strbuf args; wchar_t wcmd[MAX_PATH], wdir[MAX_PATH], *wargs, *wenvblk = NULL; unsigned flags = CREATE_UNICODE_ENVIRONMENT; @@ -1408,11 +1413,23 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen CloseHandle(cons); } memset(&si, 0, sizeof(si)); - si.cb = sizeof(si); - si.dwFlags = STARTF_USESTDHANDLES; - si.hStdInput = winansi_get_osfhandle(fhin); - si.hStdOutput = winansi_get_osfhandle(fhout); - si.hStdError = winansi_get_osfhandle(fherr); + si.StartupInfo.cb = sizeof(si); + si.StartupInfo.hStdInput = winansi_get_osfhandle(fhin); + si.StartupInfo.hStdOutput = winansi_get_osfhandle(fhout); + si.StartupInfo.hStdError = winansi_get_osfhandle(fherr); + + /* The list of handles cannot contain duplicates */ + if (si.StartupInfo.hStdInput != INVALID_HANDLE_VALUE) + stdhandles[stdhandles_count++] = si.StartupInfo.hStdInput; + if (si.StartupInfo.hStdOutput != INVALID_HANDLE_VALUE && + si.StartupInfo.hStdOutput != si.StartupInfo.hStdInput) + stdhandles[stdhandles_count++] = si.StartupInfo.hStdOutput; + if (si.StartupInfo.hStdError != INVALID_HANDLE_VALUE && + si.StartupInfo.hStdError != si.StartupInfo.hStdInput && + si.StartupInfo.hStdError != si.StartupInfo.hStdOutput) + stdhandles[stdhandles_count++] = si.StartupInfo.hStdError; + if (stdhandles_count) + si.StartupInfo.dwFlags |= STARTF_USESTDHANDLES; /* executables and the current directory don't support long paths */ if (*argv && !strcmp(cmd, *argv)) @@ -1446,16 +1463,97 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen wenvblk = make_environment_block(deltaenv); memset(&pi, 0, sizeof(pi)); - ret = CreateProcessW(*wcmd ? wcmd : NULL, wargs, NULL, NULL, TRUE, - flags, wenvblk, dir ? wdir : NULL, &si, &pi); + if (restrict_handle_inheritance && stdhandles_count && + (InitializeProcThreadAttributeList(NULL, 1, 0, &size) || + GetLastError() == ERROR_INSUFFICIENT_BUFFER) && + (attr_list = (LPPROC_THREAD_ATTRIBUTE_LIST) + (HeapAlloc(GetProcessHeap(), 0, size))) && + InitializeProcThreadAttributeList(attr_list, 1, 0, &size) && + UpdateProcThreadAttribute(attr_list, 0, + PROC_THREAD_ATTRIBUTE_HANDLE_LIST, + stdhandles, + stdhandles_count * sizeof(HANDLE), + NULL, NULL)) { + si.lpAttributeList = attr_list; + flags |= EXTENDED_STARTUPINFO_PRESENT; + } + + ret = CreateProcessW(*wcmd ? wcmd : NULL, wargs, NULL, NULL, + stdhandles_count ? TRUE : FALSE, + flags, wenvblk, dir ? wdir : NULL, + &si.StartupInfo, &pi); + + /* + * On Windows 2008 R2, it seems that specifying certain types of handles + * (such as FILE_TYPE_CHAR or FILE_TYPE_PIPE) will always produce an + * error. Rather than playing finicky and fragile games, let's just try + * to detect this situation and simply try again without restricting any + * handle inheritance. This is still better than failing to create + * processes. + */ + if (!ret && restrict_handle_inheritance && stdhandles_count) { + DWORD err = GetLastError(); + struct strbuf buf = STRBUF_INIT; + + if (err != ERROR_NO_SYSTEM_RESOURCES && + /* + * On Windows 7 and earlier, handles on pipes and character + * devices are inherited automatically, and cannot be + * specified in the thread handle list. Rather than trying + * to catch each and every corner case (and running the + * chance of *still* forgetting a few), let's just fall + * back to creating the process without trying to limit the + * handle inheritance. + */ + !(err == ERROR_INVALID_PARAMETER && + GetVersion() >> 16 < 9200) && + !getenv("SUPPRESS_HANDLE_INHERITANCE_WARNING")) { + DWORD fl = 0; + int i; + + setenv("SUPPRESS_HANDLE_INHERITANCE_WARNING", "1", 1); + + for (i = 0; i < stdhandles_count; i++) { + HANDLE h = stdhandles[i]; + strbuf_addf(&buf, "handle #%d: %p (type %lx, " + "handle info (%d) %lx\n", i, h, + GetFileType(h), + GetHandleInformation(h, &fl), + fl); + } + strbuf_addstr(&buf, "\nThis is a bug; please report it " + "at\nhttps://github.com/git-for-windows/" + "git/issues/new\n\n" + "To suppress this warning, please set " + "the environment variable\n\n" + "\tSUPPRESS_HANDLE_INHERITANCE_WARNING=1" + "\n"); + } + restrict_handle_inheritance = 0; + flags &= ~EXTENDED_STARTUPINFO_PRESENT; + ret = CreateProcessW(*wcmd ? wcmd : NULL, wargs, NULL, NULL, + TRUE, flags, wenvblk, dir ? wdir : NULL, + &si.StartupInfo, &pi); + if (ret && buf.len) { + errno = err_win_to_posix(GetLastError()); + warning("failed to restrict file handles (%ld)\n\n%s", + err, buf.buf); + } + strbuf_release(&buf); + } else if (!ret) + errno = err_win_to_posix(GetLastError()); + + if (si.lpAttributeList) + DeleteProcThreadAttributeList(si.lpAttributeList); + if (attr_list) + HeapFree(GetProcessHeap(), 0, attr_list); free(wenvblk); free(wargs); - if (!ret) { - errno = ENOENT; + if (!ret) return -1; - } + CloseHandle(pi.hThread); /* diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh index 6f0b32d875..a51c2da8cc 100755 --- a/t/t0061-run-command.sh +++ b/t/t0061-run-command.sh @@ -12,7 +12,7 @@ cat >hello-script <<-EOF cat hello-script EOF -test_expect_failure MINGW 'subprocess inherits only std handles' ' +test_expect_success MINGW 'subprocess inherits only std handles' ' test-tool run-command inherited-handle '