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Native symlinks support without UAC disable #13

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Native symlinks support without UAC disable #13

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1c9304d
Add ability to use NTFS native directory symlinks without admin right…
Karlson2k Sep 23, 2015
0dc9ce3
Use native symlinks by default
Karlson2k Sep 23, 2015
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11 changes: 10 additions & 1 deletion winsup/cygwin/environ.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -81,9 +81,18 @@ static void
set_winsymlinks (const char *buf)
{
if (!buf || !*buf)
allow_winsymlinks = WSYM_lnk;
allow_winsymlinks = WSYM_safenative;
else if (ascii_strncasematch (buf, "lnk", 3))
allow_winsymlinks = WSYM_lnk;
else if (ascii_strncasematch (buf, "safenative", 10))
{
if (ascii_strcasematch (buf + 10, "strict"))
allow_winsymlinks = WSYM_safenativestrict;
else if (ascii_strcasematch (buf + 10, "only"))
allow_winsymlinks = WSYM_safenativeonly;
else
allow_winsymlinks = WSYM_safenative;
}
/* Make sure to try native symlinks only on systems supporting them. */
else if (ascii_strncasematch (buf, "native", 6))
{
Expand Down
7 changes: 5 additions & 2 deletions winsup/cygwin/globals.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,10 @@ enum winsym_t
WSYM_lnk,
WSYM_native,
WSYM_nativestrict,
WSYM_nfs
WSYM_nfs,
WSYM_safenative,
WSYM_safenativestrict,
WSYM_safenativeonly
};

exit_states NO_COPY exit_state;
Expand All @@ -75,7 +78,7 @@ bool ignore_case_with_glob;
bool pipe_byte;
bool reset_com;
bool wincmdln;
winsym_t allow_winsymlinks = WSYM_sysfile;
winsym_t allow_winsymlinks = WSYM_safenative;

bool NO_COPY in_forkee;

Expand Down
215 changes: 213 additions & 2 deletions winsup/cygwin/path.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1846,6 +1846,207 @@ symlink_native (const char *oldpath, path_conv &win32_newpath)
return 0;
}

static int
symlink_safenative (const char *oldpath, path_conv &win32_newpath)
{
tmp_pathbuf tp;
path_conv win32_oldpath;
PUNICODE_STRING nt_oldpath;
NTSTATUS status;
HANDLE fh;
OBJECT_ATTRIBUTES attr;
IO_STATUS_BLOCK io;
PREPARSE_DATA_BUFFER prdb;
ACCESS_MASK access_mask;

syscall_printf ("symlink_safenative (oldpath: '%s', newpath: '%s')", oldpath,
win32_newpath.get_posix ());

/* Directory junction cannot be created on remote drive.
Leave this check here to simplify routing in symlink_worker(). */
if (win32_newpath.isremote ())
{
debug_printf ("'%S' is on remote drive",
win32_newpath.get_nt_native_path ());
set_errno (EXDEV);
return -1;
}

win32_oldpath.check (oldpath, PC_SYM_NOFOLLOW);

/* Make sure that symlink target is directory as directory junction
can point only to directory. If target is not exist yet then
don't create junction to prevent an invalid state with junction
pointing to later created regular file. */
if (!win32_oldpath.exists () || !win32_oldpath.isdir ())
{
debug_printf ("'%S' does not exist or is not a directory",
win32_oldpath.get_nt_native_path ());
set_errno (ENOTDIR);
return -1;
}

nt_oldpath = win32_oldpath.get_nt_native_path ();

/* Directory junction can point only to local mounted drive. */
if (nt_oldpath->Length < 6 * sizeof (wchar_t) ||
nt_oldpath->Buffer[5] != L':')
{
debug_printf ("'%S' is not on local mounted drive", nt_oldpath);
set_errno (EXDEV);
return -1;
}

/* Make sure that slash for root directory is present otherwise OS will
misbehavior when resolving such junction. This is an extra care as
get_nt_native_path() should return correct path. */
if (nt_oldpath->Length < 7 * sizeof (wchar_t) ||
nt_oldpath->Buffer[6] != L'\\')
{
set_errno (ENOTDIR);
return -1;
}

if (offsetof (REPARSE_DATA_BUFFER, MountPointReparseBuffer.PathBuffer) +
nt_oldpath->Length * 2 + (2 - 4) * sizeof (wchar_t)
> MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
{
set_errno (ENAMETOOLONG);
return -1;
}

#if MAXIMUM_REPARSE_DATA_BUFFER_SIZE > NT_MAX_PATH
#error REPARSE_DATA_BUFFER do not fit into tmp_pathbuf::c_get() buffer. Rewrite code.
#endif
prdb = (PREPARSE_DATA_BUFFER) tp.c_get ();

prdb->Reserved = 0;
prdb->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
prdb->MountPointReparseBuffer.SubstituteNameOffset = 0;
memcpy(prdb->MountPointReparseBuffer.PathBuffer, nt_oldpath->Buffer,
nt_oldpath->Length);
prdb->MountPointReparseBuffer.SubstituteNameLength =
(USHORT)(nt_oldpath->Length);
prdb->MountPointReparseBuffer.PathBuffer[
prdb->MountPointReparseBuffer.SubstituteNameLength / sizeof (wchar_t)] = 0;
prdb->MountPointReparseBuffer.PrintNameOffset =
prdb->MountPointReparseBuffer.SubstituteNameLength + 1 * sizeof (wchar_t);
memcpy(&(prdb->MountPointReparseBuffer.PathBuffer[
prdb->MountPointReparseBuffer.PrintNameOffset / sizeof (wchar_t)]),
&(nt_oldpath->Buffer[4]), nt_oldpath->Length - 4 * sizeof (wchar_t));
prdb->MountPointReparseBuffer.PrintNameLength =
(USHORT)(nt_oldpath->Length - 4 * sizeof (wchar_t));
prdb->MountPointReparseBuffer.PathBuffer[
(prdb->MountPointReparseBuffer.PrintNameOffset +
prdb->MountPointReparseBuffer.PrintNameLength) / sizeof (wchar_t)] = 0;
prdb->ReparseDataLength = (USHORT) offsetof(REPARSE_DATA_BUFFER,
MountPointReparseBuffer.PathBuffer) -
REPARSE_DATA_BUFFER_HEADER_SIZE +
prdb->MountPointReparseBuffer.PrintNameOffset +
prdb->MountPointReparseBuffer.PrintNameLength + 1 * sizeof (wchar_t);

/* DELETE access is required to delete empty directory if it's not
transformed into directory junctions. */
access_mask = FILE_WRITE_ATTRIBUTES | FILE_LIST_DIRECTORY |
FILE_TRAVERSE | SYNCHRONIZE | DELETE;
/* READ_CONTROL and WRITE_DAC are required for reuse handle in
set_file_attribute() otherwise function will need to reopen file. */
if (win32_newpath.has_acls ())
access_mask |= READ_CONTROL | WRITE_DAC;

status = NtCreateFile (&fh, access_mask,
win32_newpath.get_object_attr (attr, sec_none_nih),
&io, NULL, FILE_ATTRIBUTE_DIRECTORY,
0, FILE_CREATE, FILE_DIRECTORY_FILE |
FILE_OPEN_REPARSE_POINT | FILE_OPEN_FOR_BACKUP_INTENT,
NULL, 0);
if (!NT_SUCCESS (status))
{
if (status == STATUS_ACCESS_DENIED)
{
ULONG share_access;
/* Retry with less requested access rights. */
debug_printf ("Creating '%S' with restricted access rights",
win32_newpath.get_nt_native_path ());

access_mask &= ~(DELETE | READ_CONTROL | WRITE_DAC);

/* Allow sharing otherwise set_file_attribute() will fail. */
share_access = win32_newpath.has_acls () ? (FILE_SHARE_READ |
FILE_SHARE_WRITE) : 0;
status = NtCreateFile (&fh, access_mask,
win32_newpath.get_object_attr (attr, sec_none_nih),
&io, NULL, FILE_ATTRIBUTE_DIRECTORY,
share_access, FILE_CREATE, FILE_DIRECTORY_FILE |
FILE_OPEN_REPARSE_POINT |
FILE_OPEN_FOR_BACKUP_INTENT, NULL, 0);
}
if (!NT_SUCCESS (status))
{
debug_printf ("Creating '%S' failed, status = %y",
win32_newpath.get_nt_native_path (), status);
__seterrno_from_nt_status (status);
return -1;
}
}

if (win32_newpath.has_acls ())
set_file_attribute (fh, win32_newpath, ILLEGAL_UID, ILLEGAL_GID,
S_JUSTCREATED | S_IFDIR | S_IFLNK |
STD_RBITS | STD_WBITS | STD_XBITS);

debug_printf ("Setting SubstituteName '%W' and PrintName '%W' for directory junction '%S'",
prdb->MountPointReparseBuffer.PathBuffer +
prdb->MountPointReparseBuffer.SubstituteNameOffset / sizeof (wchar_t),
prdb->MountPointReparseBuffer.PathBuffer +
prdb->MountPointReparseBuffer.PrintNameOffset / sizeof (wchar_t),
win32_newpath.get_nt_native_path ());
status = NtFsControlFile (fh, NULL, NULL, NULL, &io, FSCTL_SET_REPARSE_POINT,
prdb, (ULONG)(prdb->ReparseDataLength +
REPARSE_DATA_BUFFER_HEADER_SIZE), NULL, 0);
if (status == STATUS_PENDING)
{
if (WaitForSingleObject (fh, 2000) == WAIT_OBJECT_0)
status = io.Status;
else
status = STATUS_ACCESS_DENIED;
}

if (!NT_SUCCESS (status))
{
FILE_DISPOSITION_INFORMATION disp = { TRUE };
if (status == STATUS_IO_REPARSE_TAG_INVALID || status == STATUS_IO_REPARSE_DATA_INVALID)
debug_printf ("Setting reparse point failed because reparse point data is invalid, status = %y", status);
else
debug_printf ("Setting reparse point failed, status = %y", status);
__seterrno_from_nt_status (status);

/* Delete created junction blank. */
status = NtSetInformationFile (fh, &io, &disp, sizeof (disp),
FileDispositionInformation);
NtClose (fh);
if (!NT_SUCCESS (status))
{
/* Reopen junction blank for deletion. */
status = NtCreateFile (&fh, DELETE,
win32_newpath.get_object_attr (attr, sec_none_nih),
&io, NULL, FILE_ATTRIBUTE_DIRECTORY,
FILE_SHARE_DELETE, FILE_OPEN, FILE_DIRECTORY_FILE |
FILE_OPEN_REPARSE_POINT | FILE_OPEN_FOR_BACKUP_INTENT |
FILE_DELETE_ON_CLOSE, NULL, 0);
if (NT_SUCCESS (status))
NtClose (fh);
}
if (!NT_SUCCESS (status) && status != STATUS_DELETE_PENDING)
debug_printf ("Removing directory junction blank failed, status = %y", status);

return -1;
}

NtClose (fh);
return 0;
}

int
symlink_worker (const char *oldpath, const char *newpath, bool isdevice)
{
Expand Down Expand Up @@ -1910,7 +2111,10 @@ symlink_worker (const char *oldpath, const char *newpath, bool isdevice)
wsym_type = WSYM_nativestrict;
}
/* Don't try native symlinks on FSes not supporting reparse points. */
else if ((wsym_type == WSYM_native || wsym_type == WSYM_nativestrict)
else if ((wsym_type == WSYM_native || wsym_type == WSYM_nativestrict
|| wsym_type == WSYM_safenative
|| wsym_type == WSYM_safenativestrict
|| wsym_type == WSYM_safenativeonly)
&& !(win32_newpath.fs_flags () & FILE_SUPPORTS_REPARSE_POINTS))
wsym_type = WSYM_sysfile;

Expand Down Expand Up @@ -1950,13 +2154,20 @@ symlink_worker (const char *oldpath, const char *newpath, bool isdevice)
case WSYM_nfs:
res = symlink_nfs (oldpath, win32_newpath);
__leave;
case WSYM_safenative:
case WSYM_safenativestrict:
case WSYM_safenativeonly:
res = symlink_safenative (oldpath, win32_newpath);
if (!res || wsym_type == WSYM_safenativeonly)
__leave;
/* Intentional fall-through */
case WSYM_native:
case WSYM_nativestrict:
res = symlink_native (oldpath, win32_newpath);
if (!res)
__leave;
/* Strictly native? Too bad. */
if (wsym_type == WSYM_nativestrict)
if (wsym_type == WSYM_nativestrict || wsym_type == WSYM_safenativestrict)
{
__seterrno ();
__leave;
Expand Down