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mingw: fix getcwd when the parent directory cannot be queried

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`GetLongPathName()` function may fail when it is unable to query
the parent directory of a path component to determine the long name
for that component. It happens, because it uses `FindFirstFile()`
function for each next short part of path. The `FindFirstFile()`
requires `List Directory` and `Synchronize` desired access for a calling
process.

In case of lacking such permission for some part of path,
the `GetLongPathName()` returns 0 as result and `GetLastError()`
returns ERROR_ACCESS_DENIED.

`GetFinalPathNameByHandle()` function can help in such cases, because
it requires `Read Attributes` and `Synchronize` desired access to the
target path only.

The `GetFinalPathNameByHandle()` function was introduced on
`Windows Server 2008/Windows Vista`. So we need to load it dynamically.

`CreateFile()` parameters:
    `lpFileName` = path to the current directory
    `dwDesiredAccess` = 0 (it means `Read Attributes` and `Synchronize`)
    `dwShareMode` = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE
                    (it prevents `Sharing Violation`)
    `lpSecurityAttributes` = NULL (default security attributes)
    `dwCreationDisposition` = OPEN_EXISTING
                              (required to obtain a directory handle)
    `dwFlagsAndAttributes` = FILE_FLAG_BACKUP_SEMANTICS
                             (required to obtain a directory handle)
    `hTemplateFile` = NULL (when opening an existing file or directory,
                            `CreateFile` ignores this parameter)

The string that is returned by `GetFinalPathNameByHandle()` function
uses the \\?\ syntax. To skip the prefix and convert backslashes
to slashes, the `normalize_ntpath()` mingw function will be used.

Note: `GetFinalPathNameByHandle()` function returns a final path.
It is the path that is returned when a path is fully resolved.
For example, for a symbolic link named "C:\tmp\mydir" that points to
"D:\yourdir", the final path would be "D:\yourdir".

Signed-off-by: Anton Serbulov <aserbulov@plesk.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Anton Serbulov 2018-10-23 03:52:49 -07:00 committed by Junio C Hamano
parent 937974fc65
commit 4745feeb8b
1 changed files with 39 additions and 0 deletions
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39
compat/mingw.c
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@ -202,6 +202,31 @@ static int ask_yes_no_if_possible(const char *format, ...)
}
}
/* Normalizes NT paths as returned by some low-level APIs. */
static wchar_t *normalize_ntpath(wchar_t *wbuf)
{
int i;
/* fix absolute path prefixes */
if (wbuf[0] == '\\') {
/* strip NT namespace prefixes */
if (!wcsncmp(wbuf, L"\\??\\", 4) ||
!wcsncmp(wbuf, L"\\\\?\\", 4))
wbuf += 4;
else if (!wcsnicmp(wbuf, L"\\DosDevices\\", 12))
wbuf += 12;
/* replace remaining '...UNC\' with '\\' */
if (!wcsnicmp(wbuf, L"UNC\\", 4)) {
wbuf += 2;
*wbuf = '\\';
}
}
/* convert backslashes to slashes */
for (i = 0; wbuf[i]; i++)
if (wbuf[i] == '\\')
wbuf[i] = '/';
return wbuf;
}
int mingw_unlink(const char *pathname)
{
int ret, tries = 0;
@ -925,6 +950,20 @@ char *mingw_getcwd(char *pointer, int len)
return NULL;
}
ret = GetLongPathNameW(cwd, wpointer, ARRAY_SIZE(wpointer));
if (!ret && GetLastError() == ERROR_ACCESS_DENIED) {
HANDLE hnd = CreateFileW(cwd, 0,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
if (hnd == INVALID_HANDLE_VALUE)
return NULL;
ret = GetFinalPathNameByHandleW(hnd, wpointer, ARRAY_SIZE(wpointer), 0);
CloseHandle(hnd);
if (!ret || ret >= ARRAY_SIZE(wpointer))
return NULL;
if (xwcstoutf(pointer, normalize_ntpath(wpointer), len) < 0)
return NULL;
return pointer;
}
if (!ret || ret >= ARRAY_SIZE(wpointer))
return NULL;
if (xwcstoutf(pointer, wpointer, len) < 0)