On Wed, Sep 12, 2018 at 5:27 AM, Oleg Nesterov <[email protected]> wrote: > On 09/11, Kees Cook wrote: >> >> Oh, I like this patch! This is much cleaner. > > it's pity. cause this means I will have to actually test this change and > (worse) write the changelog ;)
Hehe. I know this pain well! :) >> > @@ -410,11 +365,6 @@ static int bprm_mm_init(struct linux_binprm *bprm) >> > if (!mm) >> > goto err; >> > >> > - /* Save current stack limit for all calculations made during exec. >> > */ >> > - task_lock(current->group_leader); >> > - bprm->rlim_stack = current->signal->rlim[RLIMIT_STACK]; >> > - task_unlock(current->group_leader); >> > - >> >> I would prefer this hunk stay here since it will be more robust >> against weird arch-specific things happening against rlim_stack. I had >> to clean up some of these tests in arch code, so I'm nervous about >> moving this further away. Here is before we call arch_bprm_mm_init(), >> and I think it's better to do this as early as possible. > > Well, I don't reaally agree but I won't argue, this is cosmetic at least > right now. Probably what it deserves is a better comment to capture what I said above. Maybe: - /* Save current stack limit for all calculations made during exec. */ + /* Do this before any arch-specific calls, like arch_bprm_mm_init(), + * so that bprm->rlim_stack is available for the architecture to use + * in case it needs it earlier that mm layout time. + */ >> BTW, in re-reading create_elf_tables() and its calculation of "items", >> I realize the above should actually include the trailing NULL pointers >> and argc, so it should be: >> >> ptr_size = (1 + bprm->argc + 1 + bprm->envc + 1) * sizeof(void *); > > Yes, I noticed this too. But can we do this later please? Sure! >> > - unsigned long p; /* current top of mem */ >> > + unsigned long p, p_min; /* current top of mem */ >> >> Can you split this out to a separate line (with a new comment) to >> avoid comment-confusion? Something like: >> >> unsigned long p; /* current top of mem */ >> unsigned long p_min; /* the minimum allowed mem position */ > > OK, but "minimum allowed mem position" explains nothing... The comment > should explain that ->p_min (can you suggest a better name?) is artificial > marker pre-computed for rlim-like checks in copy_strings()... How about something like: ... p; /* top of memory array reserved for stack */ ... p_min; /* bottom of stack as computed in prepare_arg_pages() */ (Is "p" really only used for stack reservation tracking?) > BTW. I think we can simply kill count(). But this needs another cleanup > and dicsussion. Hm, I think we need count for doing the sanity checking and allowing the cond_resched() calls. -Kees -- Kees Cook Pixel Security
