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joystick: Allow libudev to be disabled at runtime

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Device enumeration via libudev can fail in a container for two reasons:

* the netlink protocol between udevd and libudev is considered private,
  so there is no API guarantee that the version of libudev in a container
  will understand netlink messages from a dissimilar version of udevd
  on the host system;
* the netlink protocol between udevd and libudev relies for security on
  being able to check the uid of each message, but in a container with
  a user namespace where host uid 0 is not mapped, the libudev client
  cannot distinguish between messages from host uid 0 and messages from
  a different, malicious user on the host

To make this easier to experiment with, always compile the fallback
code path even if libudev is disabled. libudev remains the default if
enabled at compile time, but the fallback code path can be forced.

Signed-off-by: Simon McVittie <smcv@collabora.com>
This commit is contained in:
Simon McVittie 2020-11-11 19:14:11 -08:00
parent 72379ba510
commit 13e7d1a958
1 changed files with 81 additions and 35 deletions
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80
src/joystick/linux/SDL_sysjoystick.c
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@ -84,6 +84,19 @@
#define DEBUG_INPUT_EVENTS 1
#endif
typedef enum
{
ENUMERATION_UNSET,
ENUMERATION_LIBUDEV,
ENUMERATION_FALLBACK
} EnumerationMethod;
#if SDL_USE_LIBUDEV
static EnumerationMethod enumeration_method = ENUMERATION_UNSET;
#else
const EnumerationMethod enumeration_method = ENUMERATION_FALLBACK;
#endif
static int MaybeAddDevice(const char *path);
#if SDL_USE_LIBUDEV
static int MaybeRemoveDevice(const char *path);
@ -108,10 +121,8 @@ static SDL_joylist_item *SDL_joylist = NULL;
static SDL_joylist_item *SDL_joylist_tail = NULL;
static int numjoysticks = 0;
#if !SDL_USE_LIBUDEV
static Uint32 last_joy_detect_time;
static time_t last_input_dir_mtime;
#endif
#define test_bit(nr, addr) \
(((1UL << ((nr) % (sizeof(long) * 8))) & ((addr)[(nr) / (sizeof(long) * 8)])) != 0)
@ -147,15 +158,8 @@ IsVirtualJoystick(Uint16 vendor, Uint16 product, Uint16 version, const char *nam
#endif /* SDL_JOYSTICK_HIDAPI */
static int
IsJoystick(int fd, char **name_return, SDL_JoystickGUID *guid)
GuessIsJoystick(int fd)
{
struct input_id inpid;
Uint16 *guid16 = (Uint16 *)guid->data;
char *name;
char product_string[128];
#if !SDL_USE_LIBUDEV
/* When udev is enabled we only get joystick devices here, so there's no need to test them */
unsigned long evbit[NBITS(EV_MAX)] = { 0 };
unsigned long keybit[NBITS(KEY_MAX)] = { 0 };
unsigned long absbit[NBITS(ABS_MAX)] = { 0 };
@ -170,7 +174,22 @@ IsJoystick(int fd, char **name_return, SDL_JoystickGUID *guid)
test_bit(ABS_X, absbit) && test_bit(ABS_Y, absbit))) {
return 0;
}
#endif
return 1;
}
static int
IsJoystick(int fd, char **name_return, SDL_JoystickGUID *guid)
{
struct input_id inpid;
Uint16 *guid16 = (Uint16 *)guid->data;
char *name;
char product_string[128];
/* When udev is enabled we only get joystick devices here, so there's no need to test them */
if (enumeration_method == ENUMERATION_FALLBACK && !GuessIsJoystick(fd)) {
return 0;
}
if (ioctl(fd, EVIOCGID, &inpid) < 0) {
return 0;
@ -484,11 +503,8 @@ static void SteamControllerDisconnectedCallback(int device_instance)
}
static void
LINUX_JoystickDetect(void)
LINUX_FallbackJoystickDetect(void)
{
#if SDL_USE_LIBUDEV
SDL_UDEV_Poll();
#else
const Uint32 SDL_JOY_DETECT_INTERVAL_MS = 3000; /* Update every 3 seconds */
Uint32 now = SDL_GetTicks();
@ -519,7 +535,20 @@ LINUX_JoystickDetect(void)
last_joy_detect_time = now;
}
}
static void
LINUX_JoystickDetect(void)
{
#if SDL_USE_LIBUDEV
if (enumeration_method == ENUMERATION_LIBUDEV) {
SDL_UDEV_Poll();
}
else
#endif
{
LINUX_FallbackJoystickDetect();
}
HandlePendingRemovals();
@ -529,6 +558,17 @@ LINUX_JoystickDetect(void)
static int
LINUX_JoystickInit(void)
{
#if SDL_USE_LIBUDEV
if (enumeration_method == ENUMERATION_UNSET) {
if (SDL_getenv("SDL_JOYSTICK_DISABLE_UDEV") != NULL) {
enumeration_method = ENUMERATION_FALLBACK;
}
else {
enumeration_method = ENUMERATION_LIBUDEV;
}
}
#endif
/* First see if the user specified one or more joysticks to use */
if (SDL_getenv("SDL_JOYSTICK_DEVICE") != NULL) {
char *envcopy, *envpath, *delim;
@ -549,6 +589,7 @@ LINUX_JoystickInit(void)
SteamControllerDisconnectedCallback);
#if SDL_USE_LIBUDEV
if (enumeration_method == ENUMERATION_LIBUDEV) {
if (SDL_UDEV_Init() < 0) {
return SDL_SetError("Could not initialize UDEV");
}
@ -561,14 +602,17 @@ LINUX_JoystickInit(void)
/* Force a scan to build the initial device list */
SDL_UDEV_Scan();
#else
}
else
#endif
{
/* Force immediate joystick detection */
last_joy_detect_time = 0;
last_input_dir_mtime = 0;
/* Report all devices currently present */
LINUX_JoystickDetect();
#endif
}
return 0;
}
@ -1191,8 +1235,10 @@ LINUX_JoystickQuit(void)
numjoysticks = 0;
#if SDL_USE_LIBUDEV
if (enumeration_method == ENUMERATION_LIBUDEV) {
SDL_UDEV_DelCallback(joystick_udev_callback);
SDL_UDEV_Quit();
}
#endif
SDL_QuitSteamControllers();