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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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