Limits for ION Memory Allocator

[Laura Abbott]

On 7/17/19 12:31 PM, Alexander Popov wrote:
> 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!
> 

Yes, I do think that's the right approach. We're working on moving Ion
out of staging and this is something I mentioned to John Stultz. I don't
think we've thought too hard about how to do the actual limiting so
suggestions are welcome.

Thanks,
Laura

> Best regards,
> Alexander
> 
> 
> [1]: https://github.com/google/syzkaller
> [2]: https://github.com/google/syzkaller/blob/master/executor/common_linux.h
>