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Merge pull request #1188 from dscho/unprivileged-symlinks

Support creating symlinks outside elevated sessions
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dscho committed Jun 5, 2017
2 parents 04a67c2 + 45c6120 commit 13f583bedb59f9a11b3f2e91673c10c250f84576
Showing with 24 additions and 2 deletions.
  1. +24 −2 compat/mingw.c
@@ -270,6 +270,7 @@ int mingw_core_config(const char *var, const char *value)
return 0;
}

static DWORD symlink_file_flags = 0, symlink_directory_flags = 1;
DECLARE_PROC_ADDR(kernel32.dll, BOOLEAN, CreateSymbolicLinkW, LPCWSTR, LPCWSTR, DWORD);

enum phantom_symlink_result {
@@ -314,7 +315,8 @@ static enum phantom_symlink_result process_phantom_symlink(
return PHANTOM_SYMLINK_DONE;

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

errno = err_win_to_posix(GetLastError());
@@ -2656,7 +2658,7 @@ int symlink(const char *target, const char *link)
wtarget[len] = '\\';

/* create file symlink */
if (!CreateSymbolicLinkW(wlink, wtarget, 0)) {
if (!CreateSymbolicLinkW(wlink, wtarget, symlink_file_flags)) {
errno = err_win_to_posix(GetLastError());
return -1;
}
@@ -3178,6 +3180,24 @@ static void maybe_redirect_std_handles(void)
GENERIC_WRITE, FILE_FLAG_NO_BUFFERING);
}

static void adjust_symlink_flags(void)
{
/*
* Starting with Windows 10 Build 14972, symbolic links can be created
* using CreateSymbolicLink() without elevation by passing the flag
* SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE (0x02) as last
* parameter, provided the Developer Mode has been enabled. Some
* earlier Windows versions complain about this flag with an
* ERROR_INVALID_PARAMETER, hence we have to test the build number
* specifically.
*/
if (GetVersion() >= 14972 << 16) {
symlink_file_flags |= 2;
symlink_directory_flags |= 2;
}

}

#if defined(_MSC_VER)

#ifdef _DEBUG
@@ -3217,6 +3237,7 @@ int msc_startup(int argc, wchar_t **w_argv, wchar_t **w_env)
#endif

maybe_redirect_std_handles();
adjust_symlink_flags();

/* determine size of argv conversion buffer */
maxlen = wcslen(_wpgmptr);
@@ -3283,6 +3304,7 @@ void mingw_startup(void)
_startupinfo si;

maybe_redirect_std_handles();
adjust_symlink_flags();

/* get wide char arguments and environment */
si.newmode = 0;

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