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    SubjectRe: [PATCH v2 4/8] exec: Allow load_misc_binary to call prepare_binfmt unconditionally
    On Tue, May 19, 2020 at 02:08:34PM -0500, Eric W. Biederman wrote:
    > Kees Cook <keescook@chromium.org> writes:
    >
    > > On Mon, May 18, 2020 at 07:31:51PM -0500, Eric W. Biederman wrote:
    > >> [...]
    > >> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
    > >> index 8605ab4a0f89..dbb5614d62a2 100644
    > >> --- a/include/linux/binfmts.h
    > >> +++ b/include/linux/binfmts.h
    > >> @@ -26,6 +26,8 @@ struct linux_binprm {
    > >> unsigned long p; /* current top of mem */
    > >> unsigned long argmin; /* rlimit marker for copy_strings() */
    > >> unsigned int
    > >> + /* It is safe to use the creds of a script (see binfmt_misc) */
    > >> + preserve_creds:1,
    > >
    > > How about:
    > >
    > > /*
    > > * A binfmt handler will set this to True before calling
    > > * prepare_binprm() if it is safe to reuse the previous
    > > * credentials, based on bprm->file (see binfmt_misc).
    > > */
    >
    > I think that is more words saying less.
    >
    > While I agree it might be better. I don't see what your comment adds to
    > the understanding. What do you see my comment not saying that is important?

    I think your comment is aimed at the consumer of preserve_creds (i.e.
    the fs/exec.c code), whereas I think the comment should be directed at
    a binfmt author, who wants to answer the question "why would I set this
    flag?" Though I strongly hope we never have new binfmts. ;)

    --
    Kees Cook

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