On Wed, 29 Jul 2020 08:14:49 +0200
Dominique Martinet <asmad...@codewreck.org> wrote:
> Greg Kurz wrote on Tue, Jul 28, 2020:
> > > The "fd" transport layer uses 2 file descriptors passed externally
> > > and calls kernel_write()/kernel_read() on these. If files were opened
> > > without FMODE_WRITE/FMODE_READ, WARN_ON_ONCE() will fire.
>
> There already is a fix in linux-next as a39c46067c84 ("net/9p: validate
> fds in p9_fd_open")
>
> > > This adds file mode checking in p9_fd_open; this returns -EBADF to
> > > preserve the original behavior.
> >
> > So this would cause open() to fail with EBADF, which might look a bit
Oops... this seems to rather end up in mount(). :)
> > weird to userspace since it didn't pass an fd... Is this to have a
> > different error than -EIO that is returned when either rfd or wfd
> > doesn't point to an open file descriptor ? If yes, why do we care ?
>
> FWIW the solution taken just returns EIO as it would if an invalid fd
> was given, but since it did pass an fd EBADF actually makes sense to me?
>
POSIX says:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html
[EBADF]
Bad file descriptor. A file descriptor argument is out of range, refers to
no open file, or a read (write) request is made to a file that is only open
for writing (reading).
It seems that EBADF would be appropriate for both the existing and the
new error path.
> However to the second question I'm not sure I care :)
>
> > > Found by syzkaller.
>
> I'm starting to understand where David comment came from the other day,
> I guess it's still time to change my mind and submit to linus now I've
> had time to test it...
>
