Re: [PATCH v8 0/4] Introduce mseal

[Theo de Raadt]

I'd like to propose a new flag to the Linux open() system call.

It is

   O_DUPABLE

You mix it with other O_* flags to the open call, everyone is familiar
with this, it is very easy to use.

If the O_DUPABLE flag is set, the file descriptor may be cloned with
dup(), dup2() or similar call.  If not set, those calls will return with
-1 EPERM.

I know it goes strongly against the grain of ancient assumptions that
file descriptors (just like memory) are fully mutable, and therefore
managed with care.  But in these trying times, we need protection against
file descriptor desecration.

It protects programmers from accidentally making clones of file
descriptors and leaking them out of programs, like I dunno, runc.
OK, besides this one very specific place that could (maybe) use
it today, there is other code which can use this but the margin is too narrow to contain.

The documentation can describe the behaviour as similar to MAP_SEALABLE,
so that noone is shocked.

/sarc