From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexander Popov <alex.popov@linux.com>
Subject: Limits for ION Memory Allocator
Date: Wed, 17 Jul 2019 19:31:57 +0300
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Hello!

The syzkaller [1] has a trouble with fuzzing the Linux kernel with ION Memory
Allocator.

Syzkaller uses several methods [2] to limit memory consumption of the userspace
processes calling the syscalls for testing the kernel:
 - setrlimit(),
 - cgroups,
 - various sysctl.
But these methods don't work for ION Memory Allocator, so any userspace process
that has access to /dev/ion can bring the system to the out-of-memory state.

An example of a program doing that:


#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <linux/types.h>
#include <sys/ioctl.h>

#define ION_IOC_MAGIC		'I'
#define ION_IOC_ALLOC		_IOWR(ION_IOC_MAGIC, 0, \
				      struct ion_allocation_data)

struct ion_allocation_data {
	__u64 len;
	__u32 heap_id_mask;
	__u32 flags;
	__u32 fd;
	__u32 unused;
};

int main(void)
{
	unsigned long i = 0;
	int fd = -1;
	struct ion_allocation_data data = {
		.len = 0x13f65d8c,
		.heap_id_mask = 1,
		.flags = 0,
		.fd = -1,
		.unused = 0
	};

	fd = open("/dev/ion", 0);
	if (fd == -1) {
		perror("[-] open /dev/ion");
		return 1;
	}

	while (1) {
		printf("iter %lu\n", i);
		ioctl(fd, ION_IOC_ALLOC, &data);
		i++;
	}

	return 0;
}


I looked through the code of ion_alloc() and didn't find any limit checks.
Is it currently possible to limit ION kernel allocations for some process?

If not, is it a right idea to do that?
Thanks!

Best regards,
Alexander


[1]: https://github.com/google/syzkaller
[2]: https://github.com/google/syzkaller/blob/master/executor/common_linux.h