Re: [RFC] corner cases of open() on procfs symlinks

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, Jun 6, 2013 at 10:20 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>         I'm not sure whether to treat that as a bug or as a weird misfeature
> enshrined in userland ABI:
>         open("/tmp", O_CREAT, 0) => -EISDIR     // LAST_NORM case
>         open("/", O_CREAT, 0) => -EISDIR        // LAST_ROOT
>         open(".", O_CREAT, 0) => -EISDIR        // LAST_DOT
>         open("..", O_CREAT, 0) => -EISDIR       // LAST_DOTDOT
>         open("/proc/self/cwd", O_CREAT, 0) => success   // LAST_BIND
>         open("/proc/self/cwd/", O_CREAT, 0) => -EISDIR  // trailing slashes

Ok, that looks buggy. O_CREAT should definitely return EISDIR for
/proc/self/cwd too, since it's a directory. I don't think the
O_RDWR/O_WRONLY thing should matter.

>        I would obviously
> like to do that - do_last() is far too convoluted as it is; the only
> question is whether we can change the first weirdness...  Comments?

Exactly which cases does that change? I have no objections if it's
only the "LAST_BIND" case that now starts returning EISDIR. Is there
anything else it affects?

That said, obviously if something breaks, we'd have to revert it, and
as a cleanup rather than some serious bug (ie this doesn't cause
crashes or security issues), I suspect this should wait until 3.11
regardless. No?

           Linus