Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: > On Sat, May 9, 2020 at 9:30 PM Tetsuo Handa > <penguin-kernel@xxxxxxxxxxxxxxxxxxx> 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
