Input: joydev - prevent use of not validated data in JSIOCSBTNMAP ioctl

commit f8f84af5da9ee04ef1d271528656dac42a090d00 upstream.

Even though we validate user-provided inputs we then traverse past
validated data when applying the new map. The issue was originally
discovered by Murray McAllister with this simple POC (if the following
is executed by an unprivileged user it will instantly panic the system):

int main(void) {
	int fd, ret;
	unsigned int buffer[10000];

	fd = open("/dev/input/js0", O_RDONLY);
	if (fd == -1)
		printf("Error opening file\n");

	ret = ioctl(fd, JSIOCSBTNMAP & ~IOCSIZE_MASK, &buffer);
	printf("%d\n", ret);
}

The solution is to traverse internal buffer which is guaranteed to only
contain valid date when constructing the map.

Fixes: 182d679b2298 ("Input: joydev - prevent potential read overflow in ioctl")
Fixes: 999b874f4aa3 ("Input: joydev - validate axis/button maps before clobbering current ones")
Reported-by: Murray McAllister <murray.mcallister@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Alexander Larkin <avlarkin82@gmail.com>
Link: https://lore.kernel.org/r/20210620120030.1513655-1-avlarkin82@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
index 83dfe19c1b6753684e795ec7b6a3915804e899f5..1b773ea667720690dc52dc8744071b842be35cb2 100644 (file)
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -492,7 +492,7 @@ static int joydev_handle_JSIOCSBTNMAP(struct joydev *joydev,
        memcpy(joydev->keypam, keypam, len);
 
        for (i = 0; i < joydev->nkey; i++)
-               joydev->keymap[keypam[i] - BTN_MISC] = i;
+               joydev->keymap[joydev->keypam[i] - BTN_MISC] = i;
 
  out:
        kfree(keypam);