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mingw: spawned processes need to inherit only standard handles

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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.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin
2018-01-26 15:37:38 +01:00
parent 31a5d68e4e
commit cf2f73537c
2 changed files with 43 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

50
compat/mingw.c
View File

@@ -1594,8 +1594,12 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
int fhin, int fhout, int fherr)
{
static int atexit_handler_initialized;
STARTUPINFOW si;
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;
@@ -1643,11 +1647,19 @@ 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);
if (si.StartupInfo.hStdInput != INVALID_HANDLE_VALUE)
stdhandles[stdhandles_count++] = si.StartupInfo.hStdInput;
if (si.StartupInfo.hStdOutput != INVALID_HANDLE_VALUE)
stdhandles[stdhandles_count++] = si.StartupInfo.hStdOutput;
if (si.StartupInfo.hStdError != INVALID_HANDLE_VALUE)
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))
@@ -1706,8 +1718,30 @@ 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 (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);
if (si.lpAttributeList)
DeleteProcThreadAttributeList(si.lpAttributeList);
if (attr_list)
HeapFree(GetProcessHeap(), 0, attr_list);
free(wenvblk);
free(wargs);

2
t/t0061-run-command.sh
View File

@@ -13,7 +13,7 @@ cat >hello-script <<-EOF
EOF
>empty
test_expect_failure MINGW 'subprocess inherits only std handles' '
test_expect_success MINGW 'subprocess inherits only std handles' '
test-run-command inherited-handle
'