From: Johannes Schindelin <johannes.schindelin@xxxxxx> 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 VFS for 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 <johannes.schindelin@xxxxxx> --- 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 fe609239dd..cac18cc3da 100644 --- a/compat/mingw.c +++ b/compat/mingw.c @@ -1398,8 +1398,13 @@ 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; @@ -1435,11 +1440,23 @@ 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; if (*argv && !strcmp(cmd, *argv)) wcmd[0] = L'\0'; @@ -1472,16 +1489,97 @@ 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 473a3405ef..7d599675e3 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 ' -- gitgitgadget
