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win: fix race in uv_fs_event_start() (#4948)

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Fetch file metadata by handle instead of by path, otherwise there is a
race window between fetching and acting on said metadata where another
process can replace the file with another one.

There is still a potential race when upgrading the short path to a long
path but that that one is intrinsic. It's not something libuv can solve
except by refraining from calling GetLongPathName.

Fixes: https://github.com/libuv/libuv/issues/4568
This commit is contained in:
Ben Noordhuis 2025-11-29 20:21:40 +01:00 committed by GitHub
parent 8e024629fe
commit 8fc70344df
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GPG Key ID: B5690EEEBB952194
1 changed files with 59 additions and 49 deletions
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108
src/win/fs-event.c
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@ -158,14 +158,14 @@ int uv_fs_event_start(uv_fs_event_t* handle,
const char* path,
unsigned int flags) {
int is_path_dir;
size_t size;
DWORD attr, last_error;
WCHAR* dir = NULL, *dir_to_watch, *pathw = NULL;
DWORD last_error;
WCHAR* dir, *pathw = NULL;
DWORD short_path_buffer_len;
WCHAR *short_path_buffer;
WCHAR* short_path, *long_path;
WCHAR* short_path = NULL;
HANDLE file_handle = INVALID_HANDLE_VALUE;
BY_HANDLE_FILE_INFORMATION info;
short_path = NULL;
if (uv__is_active(handle))
return UV_EINVAL;
@ -181,43 +181,26 @@ int uv_fs_event_start(uv_fs_event_t* handle,
if (last_error)
goto error_uv;
/* Determine whether path is a file or a directory. */
attr = GetFileAttributesW(pathw);
if (attr == INVALID_FILE_ATTRIBUTES) {
file_handle = CreateFileW(pathw,
FILE_LIST_DIRECTORY,
FILE_SHARE_READ|FILE_SHARE_DELETE|FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OVERLAPPED,
NULL);
if (file_handle == INVALID_HANDLE_VALUE) {
last_error = GetLastError();
goto error;
}
is_path_dir = (attr & FILE_ATTRIBUTE_DIRECTORY) ? 1 : 0;
if (!GetFileInformationByHandle(file_handle, &info)) {
last_error = GetLastError();
goto error;
}
if (is_path_dir) {
/* path is a directory, so that's the directory that we will watch. */
is_path_dir = (info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) ? 1 : 0;
/* Convert to long path. */
size = GetLongPathNameW(pathw, NULL, 0);
if (size) {
long_path = (WCHAR*)uv__malloc(size * sizeof(WCHAR));
if (!long_path) {
uv_fatal_error(ERROR_OUTOFMEMORY, "uv__malloc");
}
size = GetLongPathNameW(pathw, long_path, size);
if (size) {
long_path[size] = '\0';
} else {
uv__free(long_path);
long_path = NULL;
}
if (long_path) {
uv__free(pathw);
pathw = long_path;
}
}
dir_to_watch = pathw;
} else {
if (!is_path_dir) {
/*
* path is a file. So we split path into dir & file parts, and
* watch the dir directory.
@ -252,28 +235,50 @@ short_path_done:
goto error;
}
dir_to_watch = dir;
uv__free(short_path);
short_path = NULL;
uv__free(pathw);
pathw = NULL;
}
handle->dir_handle = CreateFileW(dir_to_watch,
FILE_LIST_DIRECTORY,
FILE_SHARE_READ | FILE_SHARE_DELETE |
FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS |
FILE_FLAG_OVERLAPPED,
NULL);
if (dir) {
/* Open the containing directory and watch that instead. Events for
* other files are filtered out in uv__process_fs_event_req().
* Not super efficient but c'est ça.
*/
CloseHandle(file_handle);
file_handle = CreateFileW(dir,
FILE_LIST_DIRECTORY,
FILE_SHARE_READ|FILE_SHARE_DELETE|FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OVERLAPPED,
NULL);
uv__free(dir);
dir = NULL;
if (file_handle == INVALID_HANDLE_VALUE) {
last_error = GetLastError();
goto error;
}
if (!GetFileInformationByHandle(file_handle, &info)) {
last_error = GetLastError();
goto error;
}
/* Race with another process: directory foo in foo/bar was replaced
* with a file. Bail out with an error, we're not recursing upwards.
*/
if (!(info.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)) {
/* TODO(bnoordhuis) ERROR_DIRECTORY is translated to UV_ENOENT,
* there's currently nothing that maps to UV_ENOTDIR.
*/
last_error = ERROR_DIRECTORY;
goto error;
}
}
handle->dir_handle = file_handle;
file_handle = INVALID_HANDLE_VALUE;
if (handle->dir_handle == INVALID_HANDLE_VALUE) {
last_error = GetLastError();
goto error;
@ -325,6 +330,11 @@ error:
last_error = uv_translate_sys_error(last_error);
error_uv:
if (file_handle != INVALID_HANDLE_VALUE) {
CloseHandle(file_handle);
file_handle = INVALID_HANDLE_VALUE;
}
if (handle->path) {
uv__free(handle->path);
handle->path = NULL;