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

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=Fix 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 <>
Change-Id: I08bedd8bab51fd174e603ceeca3370bcb9bb1345
Main-Branch-Verified: Cusky Presubmit Bot <>
Reviewed-by: Roy Yang <>
Tested-by: Oleksandr Tymoshenko <>
1 file changed