[PATCH 0/1] MR8273: msvcrt: Make ioinfo for stdio fds static.

[Yuxuan Shui (＠yshui)]

In kernel32/tests/loader.c, child_process will try to write to stdout after
calling LdrShutdownProcess. LdrShutdownProcess calls DLL_PROCESS_DETACH on
msvcrt, which calls msvcrt_free_io, which frees the ioinfo blocks. So to
prevent use after free in this case, we keep the ioinfos for stdin/out/err
static.

[PATCH 1/1] msvcrt: Make ioinfo for stdio fds static.

[Yuxuan Shui]

From: Yuxuan Shui

In kernel32/tests/loader.c, child_process will try to write to stdout after
calling LdrShutdownProcess. LdrShutdownProcess calls DLL_PROCESS_DETACH on
msvcrt, which calls msvcrt_free_io, which frees the ioinfo blocks. So to
prevent use after free in this case, we keep the ioinfos for stdin/out/err
static.
---
 dlls/msvcrt/file.c | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/dlls/msvcrt/file.c b/dlls/msvcrt/file.c
index 97bfc746abc..ced01937ffa 100644
--- a/dlls/msvcrt/file.c
+++ b/dlls/msvcrt/file.c
@@ -153,7 +153,19 @@ ioinfo MSVCRT___badioinfo = { INVALID_HANDLE_VALUE, WX_TEXT };
  * array of pointers to ioinfo arrays [32]
  */
 ioinfo * MSVCRT___pioinfo[MSVCRT_MAX_FILES/MSVCRT_FD_BLOCK_SIZE] = { 0 };
-
+static ioinfo stdio_ioinfo[3];
+static RTL_CRITICAL_SECTION_DEBUG stdio_critsect_debug[3] =
+{
+    { 0, 0, &stdio_ioinfo[0].crit,
+      { &stdio_critsect_debug[0].ProcessLocksList, &stdio_critsect_debug[0].ProcessLocksList },
+      0, 0, { (DWORD_PTR)(__FILE__ ": stdin_cs") } },
+    { 0, 0, &stdio_ioinfo[1].crit,
+      { &stdio_critsect_debug[1].ProcessLocksList, &stdio_critsect_debug[1].ProcessLocksList },
+      0, 0, { (DWORD_PTR)(__FILE__ ": stdout_cs") } },
+    { 0, 0, &stdio_ioinfo[2].crit,
+      { &stdio_critsect_debug[2].ProcessLocksList, &stdio_critsect_debug[2].ProcessLocksList },
+      0, 0, { (DWORD_PTR)(__FILE__ ": stderr_cs") } },
+};
 #if _MSVCR_VER >= 80

#if _MSVCR_VER >= 140
@@ -166,14 +178,17 @@ static inline void ioinfo_set_crit_init(ioinfo *info)
 {
 }
 #else
+
+#define EF_CRIT_INIT      0x01
+
 static inline BOOL ioinfo_is_crit_init(ioinfo *info)
 {
-    return info->exflag & 1;
+    return info->exflag & EF_CRIT_INIT;
 }

static inline void ioinfo_set_crit_init(ioinfo *info)
 {
-    info->exflag |= 1;
+    info->exflag |= EF_CRIT_INIT;
 }
 #endif

@@ -242,6 +257,25 @@ static inline void ioinfo_set_unicode(ioinfo *info, BOOL unicode)
 }
 #endif

+#if _MSVCR_VER >= 140
+static ioinfo stdio_ioinfo[3] =
+{
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[0], -1, 0, 0, 0, 0 } },
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[1], -1, 0, 0, 0, 0 } },
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[2], -1, 0, 0, 0, 0 } },
+};
+#else
+static ioinfo stdio_ioinfo[3] =
+{
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[0], -1, 0, 0, 0, 0 },
+      .exflag = EF_CRIT_INIT },
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[1], -1, 0, 0, 0, 0 },
+      .exflag = EF_CRIT_INIT },
+    { .handle = INVALID_HANDLE_VALUE, .crit = { &stdio_critsect_debug[2], -1, 0, 0, 0, 0 },
+      .exflag = EF_CRIT_INIT },
+};
+#endif
+
 typedef struct {
     FILE file;
     CRITICAL_SECTION crit;
@@ -394,6 +428,8 @@ static void time_to_filetime( __time64_t time, FILETIME *ft )
 static inline ioinfo* get_ioinfo_nolock(int fd)
 {
     ioinfo *ret = NULL;
+    if(fd>=0 && fd<3)
+        return &stdio_ioinfo[fd];
     if(fd>=0 && fd<MSVCRT_MAX_FILES)
         ret = MSVCRT___pioinfo[fd/MSVCRT_FD_BLOCK_SIZE];
     if(!ret)

[Yuxuan Shui (＠yshui)]

Judging from the test failures in msvcrt, this probably isn't right.

[Alexandre Julliard (＠julliard)]

There shouldn't be any need to free memory on process exit, all we need is to flush pending buffers.

[Yuxuan Shui (＠yshui)]

On Wed Jun 11 14:22:09 2025 +0000, Alexandre Julliard wrote:
> There shouldn't be any need to free memory on process exit, all we need
> is to flush pending buffers.

Opened !8288, hope I understood what you meant correctly

[PATCH 0/1] MR8273: msvcrt: Make ioinfo for stdio fds static. - closed

[Yuxuan Shui (＠yshui)]

This merge request was closed by Yuxuan Shui.