Re: Limits for ION Memory Allocator

[Joel Fernandes <joel@joelfernandes.org>]

On Wed, Jul 24, 2019 at 4:24 PM John Stultz <john.stultz@linaro.org> wrote:
>
> On Wed, Jul 24, 2019 at 1:18 PM John Stultz <john.stultz@linaro.org> wrote:
> >
> > On Wed, Jul 24, 2019 at 12:36 PM Laura Abbott <labbott@redhat.com> wrote:
> > >
> > > 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.
> >
> > In part the dmabuf heaps allow for separate heap devices, so we can
> > have finer grained permissions to the specific heaps.  But that
> > doesn't provide any controls on how much memory one process could
> > allocate using the device if it has permission.
> >
> > I suspect the same issue is present with any of the dmabuf exporters
> > (gpu/display drivers, etc), so this is less of an ION/dmabuf heap
> > issue and more of a dmabuf core accounting issue.
> >
>
> Also, do unmapped memfd buffers have similar accounting issues?
>

The syzcaller bot didn't complain about this for memfd yet, so I suspect not ;-)

With memfd since it uses shmem underneath, __vm_enough_memory() is
called during shmem_acct_block() which should take per-process memory
into account already and fail if there is not enough memory.

Should ION be doing something similar to fail if there's not enough memory?

thanks,

- Joel