[PATCH v7 4/7] fs: Introduce O_MAYEXEC flag for openat2(2)

[Florian Weimer]

* Al Viro:

> On Thu, Jul 23, 2020 at 07:12:24PM +0200, Mickaël Salaün wrote:
>> When the O_MAYEXEC flag is passed, openat2(2) may be subject to
>> additional restrictions depending on a security policy managed by the
>> kernel through a sysctl or implemented by an LSM thanks to the
>> inode_permission hook.  This new flag is ignored by open(2) and
>> openat(2) because of their unspecified flags handling.  When used with
>> openat2(2), the default behavior is only to forbid to open a directory.
>
> Correct me if I'm wrong, but it looks like you are introducing a magical
> flag that would mean "let the Linux S&M take an extra special whip
> for this open()".
>
> Why is it done during open?  If the caller is passing it deliberately,
> why not have an explicit request to apply given torture device to an
> already opened file?  Why not sys_masochism(int fd, char *hurt_flavour),
> for that matter?

While I do not think this is appropriate language for a workplace, Al
has a point: If the auditing event can be generated on an already-open
descriptor, it would also cover scenarios like this one:

  perl < /path/to/script

Where the process that opens the file does not (and cannot) know that it
will be used for execution purposes.

Thanks,
Florian