Messages in this thread | | | From | David Drysdale <> | Date | Mon, 27 Oct 2014 18:03:43 +0000 | Subject | Re: [PATCHv5 1/3] syscalls,x86: implement execveat() system call |
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On Wed, Oct 22, 2014 at 7:44 PM, Andy Lutomirski <luto@amacapital.net> wrote: > On Wed, Oct 22, 2014 at 4:44 AM, David Drysdale <drysdale@google.com> wrote: >> Add a new system execveat(2) syscall. execveat() is to execve() as >> openat() is to open(): it takes a file descriptor that refers to a >> directory, and resolves the filename relative to that. >> > >> bprm->file = file; >> - bprm->filename = bprm->interp = filename->name; >> + if (fd == AT_FDCWD || filename->name[0] == '/') { >> + bprm->filename = filename->name; >> + } else { >> + /* >> + * Build a pathname that reflects how we got to the file, >> + * either "/dev/fd/<fd>" (for an empty filename) or >> + * "/dev/fd/<fd>/<filename>". >> + */ >> + pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY); >> + if (!pathbuf) { >> + retval = -ENOMEM; >> + goto out_unmark; >> + } >> + bprm->filename = pathbuf; >> + if (filename->name[0] == '\0') >> + sprintf(pathbuf, "/dev/fd/%d", fd); > > If the fd is O_CLOEXEC, then this will result in a confused child > process. Should we fail exec attempts like that for non-static > programs? (E.g. set filename to "" or something and fix up the binfmt > drivers to handle that?)
Isn't it just scripts that get confused here (as normal executables don't get to see brpm->filename)?
Given that we don't know which we have at this point, I'd suggest carrying on regardless. Or we could fall back to use the previous best-effort d_path() code for O_CLOEXEC fds. Thoughts?
>> + else >> + snprintf(pathbuf, PATH_MAX, >> + "/dev/fd/%d/%s", fd, filename->name); > > Does this need to handle the case where the result exceeds PATH_MAX?
I guess we could kmalloc(strlen(filename->name) + 19) to avoid the possibility of failure, but that just defers the inevitable -- the interpreter won't be able to open the script file anyway. But it would at least then generate the appropriate error (ENAMETOOLONG rather than ENOENT).
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