Re: [patch 4/4] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation, v3

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Thu, Aug 21, 2014 at 03:51:15PM -0700, Andrew Morton wrote:
...
> > 
> > Still note that updating exe-file link now doesn't require sys-resource
> > capability anymore, after all there is no much profit in preventing setup
> > own file link (there are a number of ways to execute own code -- ptrace,
> > ld-preload, so that the only reliable way to find which exactly code
> > is executed is to inspect running program memory). Still we require
> > the caller to be at least user-namespace root user.
> > 
> > I believe the old interface should be deprecated and ripped off
> > in a couple of kernel releases if no one against.
> > 
> > To test if new interface is implemented in the kernel one
> > can pass PR_SET_MM_MAP_SIZE opcode and the kernel returns
> > the size of currently supported struct prctl_mm_map.
> 
> Please convince me that we're not adding any security holes.

I've commented all the fields and their purpose and triple-checked them all,
so I don't see any sec. problems, but for same purpose I've CC'ed a number
of people just to be on safe side. Again, if we want this feature to be
somehow more controlled -- we can add some sysctl variable which would
enable/disable this interface globally.

> > +	error |= __prctl_check_addr_space(start_code);
> > +	error |= __prctl_check_addr_space(end_code);
> > +	error |= __prctl_check_addr_space(start_data);
> > +	error |= __prctl_check_addr_space(end_data);
> > +	error |= __prctl_check_addr_space(start_stack);
> > +	error |= __prctl_check_addr_space(start_brk);
> > +	error |= __prctl_check_addr_space(brk);
> > +	error |= __prctl_check_addr_space(arg_start);
> > +	error |= __prctl_check_addr_space(arg_end);
> > +	error |= __prctl_check_addr_space(env_start);
> > +	error |= __prctl_check_addr_space(env_end);
> 
> Boy this is verbose.  I had a little fiddle and came up with
...
> 
> +
> +		for (i = 0; i < ARRAY_SIZE(offsets); i++) {
> +			u64 val = ((u64 *)prctl_map)[offsets[i]];
> +
> +			if (val < mmap_min_addr || val >= mmap_max_addr) {
> +				error = -EINVAL;
> +				goto out;
> +			}
> +		}
> +	}
> 
> and it saved 400 bytes of text.
> 
> But it's a bit hacky.  Can anyone think of anything smarter?

Looks good to me and not that hacky actually. Should I update on top
for -mm tree?