Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening /proc/pid/fd/N

[David Herrmann]

Hi

On Tue, Apr 22, 2014 at 5:24 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Tue, Apr 22, 2014 at 8:19 AM, David Herrmann <dh.herrmann@xxxxxxxxx> wrote:
>> In other words, the bug you describe is that /proc/pid/fd/ allows
>> access to objects without a reachable path to the only _real_
>> filesystem link. But isn't the same true for openat()?
>
> I don't think so.  openat doesn't work on fds for things that aren't
> directories.

Sorry, I wasn't precise enough: I meant the same 'leak' occurs if you
keep a dir-fd on the directory in question _before_ it is set to 0600.
Just like the example race keeps a file-fd to the file in question. So
after the directory is set to 0600 you can use that dir-fd via
openat() to avoid the whole path-lookup just like you do it via /proc.

Thanks
David
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