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.

RELEASE_NOTE=Fixed CVE-2021-3612

cos-patch: security-high
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 <>
Suggested-by: Linus Torvalds <>
Signed-off-by: Alexander Larkin <>
Signed-off-by: Dmitry Torokhov <>
Signed-off-by: Greg Kroah-Hartman <>
Change-Id: I75c17ec0b4275130a246acb54909c9d126065acb
Reviewed-by: Vaibhav Rustagi <>
Tested-by: Cusky Presubmit Bot <>
diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c
index 430dc69..675fcd0 100644
--- a/drivers/input/joydev.c
+++ b/drivers/input/joydev.c
@@ -500,7 +500,7 @@
 	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;