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Add support for creating symlinks as an unprivileged user #1184

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Add support for creating symlinks as an unprivileged user #1184

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38 changes: 36 additions & 2 deletions compat/mingw.c
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Original file line number Diff line number Diff line change
Expand Up @@ -272,6 +272,16 @@ int mingw_core_config(const char *var, const char *value)

DECLARE_PROC_ADDR(kernel32.dll, BOOL, CreateSymbolicLinkW, LPCWSTR, LPCWSTR, DWORD);

#ifndef SYMBOLIC_LINK_FLAG_DIRECTORY
#define SYMBOLIC_LINK_FLAG_DIRECTORY 0x1
#endif

#ifndef SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
#define SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE 0x2
#endif

static int has_unprivileged_symlinks = 0;

enum phantom_symlink_result {
PHANTOM_SYMLINK_RETRY,
PHANTOM_SYMLINK_DONE,
Expand All @@ -286,6 +296,7 @@ static enum phantom_symlink_result process_phantom_symlink(
const wchar_t *wtarget, const wchar_t *wlink) {
HANDLE hnd;
BY_HANDLE_FILE_INFORMATION fdata;
DWORD symlink_flags = SYMBOLIC_LINK_FLAG_DIRECTORY;

/* check that wlink is still a file symlink */
if ((GetFileAttributesW(wlink)
Expand Down Expand Up @@ -313,8 +324,13 @@ static enum phantom_symlink_result process_phantom_symlink(
if (!(fdata.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY))
return PHANTOM_SYMLINK_DONE;

/* Permit creating symlink as an unprivileged user if supported */
if (has_unprivileged_symlinks == 1) {
symlink_flags |= SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
}

/* otherwise recreate the symlink with directory flag */
if (DeleteFileW(wlink) && CreateSymbolicLinkW(wlink, wtarget, 1))
if (DeleteFileW(wlink) && CreateSymbolicLinkW(wlink, wtarget, symlink_flags))
return PHANTOM_SYMLINK_DIRECTORY;

errno = err_win_to_posix(GetLastError());
Expand Down Expand Up @@ -2639,6 +2655,7 @@ int symlink(const char *target, const char *link)
{
wchar_t wtarget[MAX_LONG_PATH], wlink[MAX_LONG_PATH];
int len;
DWORD symlink_flags = 0;

/* fail if symlinks are disabled or API is not supported (WinXP) */
if (!has_symlinks || !INIT_PROC_ADDR(CreateSymbolicLinkW)) {
Expand All @@ -2655,8 +2672,13 @@ int symlink(const char *target, const char *link)
if (wtarget[len] == '/')
wtarget[len] = '\\';

/* Permit creating symlink as an unprivileged user if supported */
if (has_unprivileged_symlinks == 1) {
symlink_flags |= SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE;
}

/* create file symlink */
if (!CreateSymbolicLinkW(wlink, wtarget, 0)) {
if (!CreateSymbolicLinkW(wlink, wtarget, symlink_flags)) {
errno = err_win_to_posix(GetLastError());
return -1;
}
Expand Down Expand Up @@ -3021,6 +3043,18 @@ static void setup_windows_environment(void)
if (!(tmp = getenv("MSYS")) || !strstr(tmp, "winsymlinks:nativestrict"))
has_symlinks = 0;

/* Check if this release of Windows supports creating symbolic links as an
* unprivileged user. The underlying API support was introduced in the
* Windows 10 Creators Update (v1703). Older releases of Windows don't
* understand the new flag to the CreateSymbolicLink family of functions.
*/
struct utsname winver;
if (uname(&winver) == 0) {
if (atoi(winver.version) >= 15063) {
has_unprivileged_symlinks = 1;

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}
}

if (!getenv("LC_ALL") && !getenv("LC_CTYPE") && !getenv("LANG"))
setenv("LC_CTYPE", "C", 1);
}
Expand Down