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 7ef6e1c165e35cef5dc17d211320966b8c85dc88..9123799365e63cf8e1a237e514fac3b0833ed5c5 100644 (file)
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -504,7 +504,7 @@ 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);