Re: [PATCHv4 RESEND 0/3] syscalls,x86: Add execveat() system call

[David Drysdale]

On Wed, Oct 22, 2014 at 6:40 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> David Drysdale <drysdale@xxxxxxxxxx> writes:
>> On Tue, Oct 21, 2014 at 5:29 AM, Eric W. Biederman
>> <ebiederm@xxxxxxxxxxxx> wrote:
>>> It is more a description of what we have done but as a magic string it
>>> is descriptive.  Documetation/devices.txt documents that /dev/fd/ should
>>> exist, making it an unambiguous path.  Further these days the kernel
>>> sets the device naming policy in dev, so I think we are strongly safe in
>>> using that path in any event.
>>>
>>> I think execveat is interesting in the kernel because the motivating
>>> cases are the cases where anything except a static executable is
>>> uninteresting.
>>
>> FYI, there is potential in the future for something other than static
>> executables -- the FreeBSD Capsicum implementation includes changes
>> to the dynamic linker to get its search path as a list of pre-opened dfds
>> (in LD_LIBRARY_PATH_FDS) rather than paths.
>
> Which still leaves open the question how do you find the dynamic
> linker.  Is that also a pre-opened dfd?

I *think* it's still effectively a path lookup of the INTERP header in
the kernel (but the pathname is restricted to be one of a set of
standard pre-registered interpreters).

> Using /dev/fd/$N is also the kind of thing that a shell or a script
> interpret could special case instead relying on a filesystem node
> to exist.

True.
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