Re: [tip:x86/mm] x86/mmap, ASLR: Do not treat unlimited-stack tasks as legacy mmap

[Jiri Kosina]

On Fri, 23 Jun 2017, Oleg Nesterov wrote:

> > We added a heuristics to treat applications with RLIMIT_STACK configured
> > to unlimited as legacy. This means:
> 
> To me this also means a minor security problem. The comment above
> PER_CLEAR_ON_SETID says "must be cleared upon setuid or setgid exec",
> but if you do "ulimit -s unlimited" before suid exec then
> ADDR_COMPAT_LAYOUT set by security checks will be ignored.

Could you please be a bit more specific here?

mmap_is_legacy() *first* checks for the ADDR_COMPAT_LAYOUT in the 
personality flags, and only then, if it's unset, RLIMIT_STACK comes to 
play.

Thanks,

-- 
Jiri Kosina
SUSE Labs