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xwayland: Check permissions on /tmp/.X11-unix

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For Xwayland, mutter creates the sockets in the standard /tmp/.X11-unix
directory.

Yet, if that directory already exists, it may have been created by
another user with full control over the created socket.

To avoid that issue, if the directory /tmp/.X11-unix already exists,
check that the permissions are as we expect, i.e. the directory belongs
to either root or the user herself, is writable and has the sticky bit.

Thanks to fabian@ritter-vogt.de for reporting that issue.

https://gitlab.gnome.org/GNOME/mutter/-/issues/1708

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1787>
This commit is contained in:
Olivier Fourdan 2021-03-18 09:56:34 +01:00
parent 7b5e855032
commit 1f1bf4cd9d
1 changed files with 44 additions and 1 deletions
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45
src/wayland/meta-xwayland.c
View File

@ -627,13 +627,56 @@ meta_xwayland_override_display_number (int number)
display_number_override = number; display_number_override = number;
} }
static gboolean
ensure_x11_unix_perms (GError **error)
{
struct stat buf;
if (lstat (X11_TMP_UNIX_DIR, &buf) != 0)
{
g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
"Failed to check permissions on directory \"%s\": %s",
X11_TMP_UNIX_DIR, g_strerror (errno));
return FALSE;
}
/* If the directory already exists, it should belong to root or ourselves ... */
if (buf.st_uid != 0 && buf.st_uid != getuid ())
{
g_set_error (error, G_IO_ERROR, G_IO_ERROR_PERMISSION_DENIED,
"Wrong ownership for directory \"%s\"",
X11_TMP_UNIX_DIR);
return FALSE;
}
/* ... be writable ... */
if ((buf.st_mode & 0022) != 0022)
{
g_set_error (error, G_IO_ERROR, G_IO_ERROR_PERMISSION_DENIED,
"Directory \"%s\" is not writable",
X11_TMP_UNIX_DIR);
return FALSE;
}
/* ... and have the sticky bit set */
if ((buf.st_mode & 01000) != 01000)
{
g_set_error (error, G_IO_ERROR, G_IO_ERROR_PERMISSION_DENIED,
"Directory \"%s\" is missing the sticky bit",
X11_TMP_UNIX_DIR);
return FALSE;
}
return TRUE;
}
static gboolean static gboolean
ensure_x11_unix_dir (GError **error) ensure_x11_unix_dir (GError **error)
{ {
if (mkdir (X11_TMP_UNIX_DIR, 01777) != 0) if (mkdir (X11_TMP_UNIX_DIR, 01777) != 0)
{ {
if (errno == EEXIST) if (errno == EEXIST)
return TRUE; return ensure_x11_unix_perms (error);
g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno), g_set_error (error, G_IO_ERROR, g_io_error_from_errno (errno),
"Failed to create directory \"%s\": %s", "Failed to create directory \"%s\": %s",