On Mon, 2017-07-10 at 00:57 -0700, Kees Cook wrote: > For a secureexec, before memory layout selection has happened, reset the > stack rlimit to something sane to avoid the caller having control over > the resulting layouts. > > $ ulimit -s > 8192 > $ ulimit -s unlimited > $ /bin/sh -c 'ulimit -s' > unlimited > $ sudo /bin/sh -c 'ulimit -s' > 8192 > > Signed-off-by: Kees Cook <keesc...@chromium.org> > --- > fs/exec.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/fs/exec.c b/fs/exec.c > index e0186db02f90..1e3463854a16 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1343,6 +1343,16 @@ void setup_new_exec(struct linux_binprm * bprm) > > /* Make sure parent cannot signal privileged process. */ > current->pdeath_signal = 0; > + > + /* > + * For secureexec, reset the stack limit to sane default to > + * avoid bad behavior from the prior rlimits. This has to > + * happen before arch_pick_mmap_layout(), which examines > + * RLIMIT_STACK, but after the point of no return to avoid > + * needing to clean up the change on failure. > + */ > + if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM) > + current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
As setup_new_exec() is called before install_exec_creds(), I think this leaves a window where the real user can change the limit again with prlimit(). Ben. > } > > arch_pick_mmap_layout(current->mm); -- Ben Hutchings Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer
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