Messages in this thread |  | | From | (Eric W. Biederman) | Date | Mon, 11 May 2020 09:33:21 -0500 | Subject | Re: [PATCH 3/5] exec: Remove recursion from search_binary_handler |
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Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Sat, May 9, 2020 at 9:30 PM Tetsuo Handa > <penguin-kernel@i-love.sakura.ne.jp> wrote: >> >> Wouldn't this change cause >> >> if (fd_binary > 0) >> ksys_close(fd_binary); >> bprm->interp_flags = 0; >> bprm->interp_data = 0; >> >> not to be called when "Search for the interpreter" failed? > > Good catch. We seem to have some subtle magic wrt the fd_binary file > descriptor, which depends on the recursive behavior.
Yes. I Tetsuo I really appreciate you noticing this. This is exactly the kind of behavior I am trying to flush out and keep from being hidden.
> I'm not seeing how to fix it cleanly with the "turn it into a loop". > Basically, that binfmt_misc use-case isn't really a tail-call.
I have reservations about installing a new file descriptor before we process the close on exec logic and the related security modules closing file descriptors that your new credentials no longer give you access to logic.
I haven't yet figured out how opening a file descriptor during exec should fit into all of that.
What I do see is that interp_data is just a parameter that is smuggled into the call of search binary handler. And the next binary handler needs to be binfmt_elf for it to make much sense, as only binfmt_elf (and binfmt_elf_fdpic) deals with BINPRM_FLAGS_EXECFD.
So I think what needs to happen is to rename bprm->interp_data to bprm->execfd, remove BINPRM_FLAGS_EXECFD and make closing that file descriptor free_bprm's responsiblity.
I hope such a change will make it easier to see all of the pieces that are intereacting during exec.
I am still asking: is the installation of that file descriptor useful if it is not exported passed to userspace as an AT_EXECFD note?
I will dig in and see what I can come up with.
Eric
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