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SubjectRe: [PATCH v2 10/15] exec: Remove do_execve_file
On Tue, Jun 30, 2020 at 09:28:10AM -0500, Eric W. Biederman wrote:
> Christoph Hellwig <hch@infradead.org> writes:
>
> > On Tue, Jun 30, 2020 at 07:14:23AM -0500, Eric W. Biederman wrote:
> >> Christoph Hellwig <hch@infradead.org> writes:
> >>
> >> > FYI, this clashes badly with my exec rework. I'd suggest you
> >> > drop everything touching exec here for now, and I can then
> >> > add the final file based exec removal to the end of my series.
> >>
> >> I have looked and I haven't even seen any exec work. Where can it be
> >> found?
> >>
> >> I have working and cleaning up exec for what 3 cycles now. There is
> >> still quite a ways to go before it becomes possible to fix some of the
> >> deep problems in exec. Removing all of these broken exec special cases
> >> is quite frankly the entire point of this patchset.
> >>
> >> Sight unseen I suggest you send me your exec work and I can merge it
> >> into my branch if we are going to conflict badly.
> >
> > https://lore.kernel.org/linux-fsdevel/20200627072704.2447163-1-hch@lst.de/T/#t
>
>
> Looking at your final patch I do not like the construct.
>
> static int __do_execveat(int fd, struct filename *filename,
> const char __user *const __user *argv,
> const char __user *const __user *envp,
> const char *const *kernel_argv,
> const char *const *kernel_envp,
> int flags, struct file *file);
>
>
> It results in a function that is full of:
> if (kernel_argv) {
> // For kernel_exeveat
> ...
> } else {
> // For ordinary exeveat
>
> }
>
> Which while understandable. I do not think results in good long term
> maintainble code.
>
> The current file paramter that I am getting rid of in my patchset is
> a stark example of that. Because of all of the if's no one realized
> that the code had it's file reference counting wrong (amoung other
> bugs).
>
> I think this is important to address as exec has already passed
> the point where people can fix all of the bugs in exec because
> the code is so hairy.
>
> I think to be maintainable and clear the code exec code is going to
> need to look something like:
>
> static int bprm_execveat(int fd, struct filename *filename,
> struct bprm *bprm, int flags);
>
> int kernel_execve(const char *filename,
> const char *const *argv, const char *const *envp, int flags)
> {
> bprm = kzalloc(sizeof(*pbrm), GFP_KERNEL);
> bprm->argc = count_kernel_strings(argv);
> bprm->envc = count_kernel_strings(envp);
> prepare_arg_pages(bprm);
> copy_strings_kernel(bprm->envc, envp, bprm);
> copy_strings_kernel(bprm->argc, argc, bprm);
> ret = bprm_execveat(AT_FDCWD, filename, bprm);
> free_bprm(bprm);
> return ret;
> }
>
> int do_exeveat(int fd, const char *filename,
> const char __user *const __user *argv,
> const char __user *const __user *envp, int flags)
> {
> bprm = kzalloc(sizeof(*pbrm), GFP_KERNEL);
> bprm->argc = count_strings(argv);
> bprm->envc = count_strings(envp);
> prepare_arg_pages(bprm);
> copy_strings(bprm->envc, envp, bprm);
> copy_strings(bprm->argc, argc, bprm);
> ret = bprm_execveat(fd, filename, bprm);
> free_bprm(bprm);
> return ret;
> }
>
> More work is required obviously to make the code above really work but
> when the dust clears a structure like that doesn't have funny edge cases
> that can hide bugs and make it tricky to change the code.

+1 to the approach.
I think Christoph's work need to be on top of Eric's.

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